Glossary

A
Absolute Alcohol
Absolute alcohol is a common name for the chemical compound ethanol. To qualify as “absolute,” the ethyl alcohol must contain no more than one percent water. In other words, absolute alcohol is liquid alcohol that is at least 99 percent pure alcohol by weight.
Absolute Error
Absolute error or absolute uncertainty is the uncertainty in a measurement, which is expressed using the relevant units. Also, absolute error may be used to express the inaccuracy in a measurement. Absolute error may be called approximation error.
Absolute Temperature
Absolute temperature is temperature measured using the Kelvin scale where zero is absolute zero. The zero point is the temperature at which particles of matter have their minimum motion and can become no colder (minimum energy). Because it is “absolute,” a thermodynamic temperature reading is not followed by a degree symbol.
Absolute Uncertainty
Absolute error or absolute uncertainty is the uncertainty in a measurement, which is expressed using the relevant units. Also, absolute error may be used to express the inaccuracy in a measurement.
Absolute Zero
Absolute zero is defined as the point where no more heat can be removed from a system, according to the absolute or thermodynamic temperature scale. This corresponds to zero Kelvin, or minus 273.15 C. This is zero on the Rankine scale and minus 459.67 F.
Absorbance
Absorbance is a measure of the quantity of light absorbed by a sample. It is also known as optical density, extinction, or decadic absorbance. The property is measured using spectroscopy, particularly for quantitative analysis. Typical units of absorbance are called “absorbance units,” which have the abbreviation AU and are dimensionless.
Absorption
Absorption is the process by which atoms, molecules, or ions enter a bulk phase (liquid, gas, solid). Absorption differs from from adsorption, since the atoms/molecules/ions are taken up by the volume, not by surface.
Accuracy
Accuracy refers to the correctness of a single measurement. Accuracy is determined by comparing the measurement against the true or accepted value. An accurate measurement is close to the true value, like hitting the center of a bullseye.
Acid
An acid is a chemical species that donates protons or hydrogen ions and/or accepts electrons. Most acids contain a hydrogen atom bonded that can release (dissociate) to yield a cation and an anion in water. The higher the concentration of hydrogen ions produced by an acid, the higher its acidity and the lower the pH of the solution.
Acid Anhydride
An acid anhydride is a nonmetal oxide which reacts with water to form an acidic solution.
In organic chemistry, an acid anhydride is a functional group consisting of two acyl groups joined together by an oxygen atom.
Acid anhydride also refers to compounds containing the acid anhydride functional group.
Acid anhydrides are named from the acids that created them. The “acid” part of the name is replaced with “anhydride.” For example, the acid anhydride formed from acetic acid would be acetic anhydride.
Acid Dissociation Constant
The acid dissociation constant is the equilibrium constant of the dissociation reaction of an acid and is denoted by Ka. This equilibrium constant is a quantitative measure of the strength of an acid in a solution. Ka is commonly expressed in units of mol/L.
Acid-Base Indicator
In chemistry and cooking, many substances dissolve in water to make it either acidic or basic/alkaline. A basic solution has a pH greater than 7, while an acidic solution has a pH of less than 7. Aqueous solutions with a pH of 7 are considered to be neutral. Acid-base indicators are substances used to determine roughly where a solution falls on the pH scale.
Acid-Base Titration
An acid-base titration is a neutralization reaction performed in the lab to determine an unknown concentration of acid or base. The moles of acid will equal the moles of the base at the equivalence point.
Acidic Solution
An acidic solution is any aqueous solution which has a pH < 7.0 ([H+] > 1.0 x 10-7 M). While it’s never a good idea to taste an unknown solution, acidic solutions are sour, in contrast to alkaline solutions, which are soapy.
Actinide
At the bottom of the periodic table is a special group of metallic radioactive elements called actinides or actinoids. These elements, usually considered ranging from atomic number 89 to atomic number 103 on the periodic table, have interesting properties, and play a key role in nuclear chemistry.
Activated Complex
An activated complex is an intermediate state that is formed during the conversion of reactants into products. An activated complex is the structure that results in the maximum energy point along the reaction path. The activation energy of a chemical reaction is the difference between the energy of the activated complex and the energy of the reactants.
Activation Energy
Activation energy is the minimum amount of energy required to initiate a reaction. It is the height of the potential energy barrier between the potential energy minima of the reactants and products. Activation energy is denoted by Ea and typically has units of kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). The term “activation energy” was introduced by the Swedish scientist Svante Arrhenius in 1889.
Active transport
Active transport is the movement of molecules or ions against a concentration gradient (from an area of lower to higher concentration), which does not ordinarily occur, so enzymes and energy are required.
Actual Yield
The actual yield is the quantity of a product that is obtained from a chemical reaction. In contrast, the calculated or theoretical yield is the amount of product that could be obtained from a reaction if all of the reactant converted to product. Theoretical yield is based on the limiting reactant.
Acyl Group
An acyl group is a functional group with formula RCO- where R is bound to the carbon atom with a single bond. Typically the acyl group is attached to a larger molecule such that the carbon and oxygen atoms are joined by a double bond.
Acyl groups are formed when one or more hydroxyl groups are removed from an oxoacid.
Even though acyl groups are almost exclusively discussed in organic chemistry, they may be derived from inorganic compounds, such as phosphonic acid and sulfonic acid.
Adenosine Triphosphate or ATP
Adenosine triphosphate or ATP is often called the energy currency of the cell because this molecule plays a key role in metabolism, particularly in energy transfer within cells. The molecule acts to couple the energy of exergonic and endergonic processes, making energetically unfavorable chemical reactions able to proceed.
Adsorption
Adsorption is defined as the adhesion of a chemical species onto the surface of particles. German physicist Heinrich Kayser coined the term “adsorption” in 1881. Adsorption is a different process from absorption, in which a substance diffuses into a liquid or solid to form a solution.
Adulterant
An adulterant is a chemical which acts as a contaminant when combined with other substances.
Adulterants are added to pure substances to extend the quantity while reducing the quality.
Aether
Aether was the fifth element in alchemical chemistry and early physics. It was the name given to the material that was believed to fill the universe beyond the terrestrial sphere. The belief in aether as an element was held by medieval alchemists, Greeks, Buddhists, Hindus, the Japanese, and the Tibetan Bon. Ancient Babylonians believed the fifth element to be the sky.
Air
Nitrogen, oxygen and argon are the three main components of the atmosphere. Water concentration varies, but averages around 0.25% of the atmosphere by mass. Carbon dioxide and all of the other elements and compounds are trace gases. Trace gases include the greenhouse gases carbon dioxide, methane, nitrous oxide, and ozone. Except for argon, other noble gases are trace elements.
Alchemy
The word “alchemy” comes from the Arabian al-kimia, referring to the preparation of elixir by the Egyptians. The Arabic kimia, in turn, comes from the Coptic khem, which refers to the fertile black Nile delta soil as well as the dark mystery of the primordial First Matter (the Khem). This is also the origin of the word “chemistry.”
Alcohol
Absolute alcohol is a common name for the chemical compound ethanol. To qualify as “absolute,” the ethyl alcohol must contain no more than one percent water. In other words, absolute alcohol is liquid alcohol that is at least 99 percent pure alcohol by weight.
Aliphatic Amino Acid
An amino acid is an organic molecule characterized by having a carboxyl group (-COOH), amino group (-NH2), and side chain. One type of side chain is aliphatic
Aliphatic Compound
An aliphatic compound is an organic compound containing carbon and hydrogen joined together in straight chains, branched chains, or non-aromatic rings. It is one of two broad classes of hydrocarbons, the other being aromatic compounds.
Open-chain compounds that contain no rings are aliphatic, whether they contain single, double, or triple bonds. In other words, they may be saturated or unsaturated. Some aliphatics are cyclic molecules, but their rings are not as stable as those of aromatic compounds. While hydrogen atoms are most commonly bound to the carbon chain, oxygen, nitrogen, sulfur, or chlorine atoms might also be present.
Aliphatic compounds are also known as aliphatic hydrocarbons or eliphatic compounds.
Aliphatic Hydrocarbon
An aliphatic compound is a hydrocarbon compound containing carbon and hydrogen joined together in straight chains, branched trains or non-aromatic rings. Aliphatic compounds may be saturated (e.g., hexane and other alkanes) or unsaturated (e.g., hexene and other alkenes, as well as alkynes).
The simplest aliphatic hydrocarbon is methane, CH4. In addition to hydrogen, other elements may be bound to the carbon atoms in the chain, including oxygen, nitrogen, chlorine, and sulfur. Most aliphatic hydrocarbons are flammable.
Alkali Metal
Alkali metals are any of the elements found in Group IA of the periodic table (the first column). Alkali metals are very reactive chemical species that readily lose their one valence electron to form ionic compounds with nonmetals. All elements in the alkali metal group occur in nature.
Alkaline
Alkaline refers to an aqueous solution having a pH greater than 7 or a [OH-] greater than 10-7. An alkaline solution is also known as basic.
Alkene Chains
An alkene is a molecule made up entirely of carbon and hydrogen where one or more carbon atoms are connected by double bonds. The general formula for an alkene is CnH2n where n is the number of carbon atoms in the molecule.
Alkenyl Group
An alkenyl group is a hydrocarbon group formed when a hydrogen atom is removed from an alkene group.
Alkenyl compounds are named by replacing the -e from the parent alkene’s name with -yl.
Alkoxide
An alkoxide is an organic functional group formed when a hydrogen atom is removed from a hydroxyl group of alcohol when reacted with a metal. It is the conjugate base of alcohol.
Alkoxy Group
An alkoxy group is a functional group containing an alkyl group (carbon and hydrogen chain) bonded to an oxygen atom. Alkoxy groups have the general formula: R-O. An alkoxy group is also known as an alkyloxy group.
Allotrope
The term allotrope refers to one or more forms of a chemical element that occur in the same physical state. The different forms arise from the different ways atoms may be bonded together. The concept of allotropes was proposed by Swedish scientist Jons Jakob Berzelius in 1841. The ability for elements to exist in this way is called allotropism.
Alloy
An alloy is a substance made by melting two or more elements together, at least one of them metal. An alloy crystallizes upon cooling into a solid solution, mixture, or intermetallic compound. The components of alloys cannot be separated using a physical means. An alloy is homogeneous and retains the properties of a metal, even though it may include metalloids or nonmetals in its composition.
Amalgam
An amalgam is a type of alloy found in dentistry, mining, mirrors and other applications. Here is a look at an amalgam’s composition, uses, and the risks associated with use.
Amide
An amide is a functional group containing a carbonyl group linked to a nitrogen atom or any compound containing the amide functional group. Amides are derived from carboxylic acid and an amine. Amide is also the name for the inorganic anion NH2. It is the conjugate base of ammonia (NH3).
Amino Acid
An amino acid is an organic compound characterized by having a carboxyl group, amino group, and side-chain attached to a central carbon atom.
Amorphous
In physics and chemistry, amorphous is a term used to describe a solid which does not exhibit crystalline structure. While there may be local ordering of the atoms or molecules in an amorphous solid, no long-term ordering is present. In older texts, the words “glass” and “glassy” were synonymous with amorphous. However, now glass is considered to be one type of amorphous solid.
Amphiprotic
Amphiprotic describes a substance that can both accept and donate a proton or H+. An amphiprotic molecule has characteristics of both and acid and a base and can act as either. It is an example of a type of amphoteric molecule.
Amphoteric
An amphoteric substance is one that can act as either an acid or a base, depending on the medium. The word comes from the Greek amphoteros or amphoteroi, meaning “each or both of two” and, essentially, “either acid or alkaline.”
Amphoteric Oxide
An amphoteric oxide is an oxide that can act as either an acid or base in a reaction to produce a salt and water. Amphoterism depends on the oxidation states available to a chemical species. Because metals have multiple oxidation states, they form amphoteric oxides and hydroxides.
Analytical Chemistry
Analytical chemistry is the chemistry discipline that studies the chemical composition of materials and develops the tools used to examine chemical compositions. It involves wet lab chemistry as well as use of instrumentation. Analytical chemistry is important in science, engineering, medicine, and industry.
Analytical chemistry makes use of standards and error analysis.
Angstrom
An angstrom or ångström is a unit of length used to measure very small distances. One angstrom is equal to 10−10 m (one ten-billionth of a meter or 0.1 nanometers). Although the unit is recognized world-wide, it is not an International System (SI) or metric unit.
The symbol for angstrom is Å, which is a letter in the Swedish alphabet.
Angular Momentum Quantum Number
The angular momentum quantum number, ℓ, is the quantum number associated with the angular momentum of an atomic electron. The angular momentum quantum number determines the shape of the electron’s orbital.
Also Known As: azimuthal quantum number, second quantum number
Anhydrous
Anhydrous literally means “no water.” In chemistry, substances without water are labeled anhydrous. The term is most often applied to crystalline substances after the water of crystallization is removed.
Anion
An anion is an ionic species having a negative charge. The chemical species may be a single atom or a group of atoms. An anion is attracted to the anode in electrolysis. Anions are typically larger than cations (positively charged ions) because they have extra electrons around them.
Anti-Markovnikov Addition
Markovnikov’s Rule describes the nature of alkene addition reactions in organic chemistry. Russian chemist Vladimir Markovnikov formulated the rule in 1865 after noting the halogen atom preferred the more substituted carbon in a hydrohalogenation reaction with an asymmetric alkene.
Anti-Periplanar
periplanar conformation where the dihedral atom between atoms is between 150° and 180°.
Antibonding Orbital
An antibonding orbital is a molecular orbital containing an electron outside the region between the two nuclei.
Antimony
Antimony is the name for the element with atomic number 36 and is represented by the symbol Kr. It is a member of the metalloid group.
Aqua Regia
Aqua regia is a mixture of hydrochloric acid (HCl) and nitric acid (HNO3) at a ratio of either 3:1 or 4:1. It is a reddish-orange or yellowish-orange fuming liquid. The term is a Latin phrase, meaning “king’s water”. The name reflects the ability of aqua regia to dissolve the noble metals gold, platinum, and palladium. Note aqua regia will not dissolve all noble metals. For example, iridium and tantalum are not dissolved.
Aqueous
Aqueous is a term used to describe a system which involves water. The word aqueous is also applied to describe a solution or mixture in which water is the solvent. When a chemical species has been dissolved in water, this is denoted by writing (aq) after the chemical name.
Aqueous Solution
An aqueous solution is any solution in which water (H2O) is the solvent. In a chemical equation, the symbol (aq) follows a species name to indicate that it is in aqueous solution.
Aroma Compounds
An odor or odour is a volatile chemical compound that humans and other animals perceive via the sense of smell or olfaction. Odors are also known as aromas or fragrances and (if they are unpleasant) as reeks, stenches, and stinks. The type of molecule that produces an odor is called an aroma compound or an odorant. These compounds are small, with molecular weights less than 300 Daltons, and are readily dispersed in the air due to their high vapor pressure. The sense of smell can detect odors are extremely low concentrations.
Arrhenius Acid
An Arrhenius acid is a substance that dissociates in water to form hydrogen ions or protons. In other words, it increases the number of H+ ions in the water. In contrast, an Arrhenius base dissociates in water to form hydroxide ions, OH-.
Arrhenius Base
An Arrhenius base is a substance that when added to water increases the number of OH- ions in the water. The base dissociates in water to form hydroxide (OH) ions. It may decrease the aqueous hydronium ion (H3O+) concentration.
Arsenic
metalloid with element symbol As and atomic number 33.
Aryl Group
An aryl group is a functional group derived from a simple aromatic ring compound where one hydrogen atom is removed from the ring. Usually, the aromatic ring is a hydrocarbon. The hydrocarbon name takes the -yl suffix, such as indolyl, thienyl, phenyl, etc. An aryl group is often simply called an “aryl”. In chemical structures, the presence of an aryl is indicated using the shorthand notation “Ar”.
Astatine
Astatine is a radioactive element with symbol At and atomic number 85. It has the distinction of being the rarest natural element found in the Earth’s crust, as it is only produced from radioactive decay of even heavier elements. The element is similar to its lighter congener, iodine. While it is a halogen (a nonmetal), it has more metallic character than other elements than the group and most likely behaves as a metalloid or even a metal. However, sufficient quantities of the element have not been produced, so its appearance and behavior as a bulk element have yet to be characterized.
Atmosphere
Atmosphere refers to the gases surrounding a star or planetary body held in place by gravity. A body is more likely to retain an atmosphere over time if gravity is high and the temperature of the atmosphere is low.
Atom
An atom is the defining structure of an element, which cannot be broken by any chemical means. A typical atom consists of a nucleus of positively-charged protons and electrically neutral neutrons with negatively-charged electrons orbiting this nucleus. However, an atom can consist of a single proton (i.e., the protium isotope of hydrogen) as a nucleus. The number of protons defines the identity of an atom or its element.
Atomic Mass
Atomic mass, which is also known as atomic weight, is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally occurring element.
Atomic mass indicates the size of an atom. Although technically the mass is the sum of the mass of all the protons, neutrons, and electrons in an atom, the mass of an electron is so much less than that of the other particles, that the mass is simply that of the nucleus (protons and neutrons).
Atomic Mass Unit
In chemistry, an atomic mass unit or AMU is a physical constant equal to one-twelfth of the mass of an unbound atom of carbon-12. It is a unit of mass used to express atomic masses and molecular masses. When the mass is expressed in AMU, it roughly reflects the sum of the number of protons and neutrons in the atomic nucleus (electrons have so much less mass that they are assumed to have a negligible effect). The symbol for the unit is u (unified atomic mass unit) or Da (Dalton), although AMU may still be used.
1 u = 1 Da = 1 amu (in modern usage) = 1 g/mol
Atomic Mass Unit
In chemistry, an atomic mass unit or AMU is a physical constant equal to one-twelfth of the mass of an unbound atom of carbon-12. It is a unit of mass used to express atomic masses and molecular masses. When the mass is expressed in AMU, it roughly reflects the sum of the number of protons and neutrons in the atomic nucleus (electrons have so much less mass that they are assumed to have a negligible effect). The symbol for the unit is u (unified atomic mass unit) or Da (Dalton), although AMU may still be used.
1 u = 1 Da = 1 amu (in modern usage) = 1 g/mol
Atomic Number
The atomic number of a chemical element is the number of protons in the nucleus of an atom of the element. It is the charge number of the nucleus since neutrons carry no net electrical charge. The atomic number determines the identity of an element and many of its chemical properties. The modern periodic table is ordered by increasing atomic number.
Atomic Radius
Atomic radius is a term used to describe the size of an atom. However, there is no standard definition for this value. The atomic radius may refer to the ionic radius, covalent radius, metallic radius, or van der Waals radius.
Atomic Solid
The definition of an atomic solid is one in which atoms of an element are bonded to other atoms of the same atom type.
Atomic Volume
The atomic volume is the volume one mole of an element occupies at room temperature. Atomic volume is typically given in cubic centimeters per mole: cc/mol. The atomic volume is a calculated value using the atomic weight and the density using the formula: atomic volume = atomic weight/density
Atomic Weight
Atomic weight is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. It is the weighted average of the masses of naturally-occurring isotopes.
Aufbau Principle
The Aufbau principle, simply put, means electrons are added to orbitals as protons are added to an atom. The term comes from the German word “aufbau”, which means “built up” or “construction”. Lower electron orbitals fill before higher orbitals do, “building up” the electron shell. The end result is that the atom, ion, or molecule forms the most stable electron configuration.
Austenite and Austenitic
Austenite is face-centered cubic iron. The term austenite is also applied to iron and steel alloys that have the FCC structure (austenitic steels). Austenite is a non-magnetic allotrope of iron. It is named for Sir William Chandler Roberts-Austen, an English metallurgist known for his studies of metal physical properties.
Avogadro’s Law
Avogadro’s Law is the relation which states that at the same temperature and pressure, equal volumes of all gases contain the same number of molecules. The law was described by Italian chemist and physicist Amedeo Avogadro in 1811.
Avogadro’s Number
Avogadro’s number, or Avogadro’s constant, is the number of particles found in one mole of a substance. It is the number of atoms in exactly 12 grams of carbon-12. This experimentally determined value is approximately 6.0221 x 1023 particles per mole.
particles per mole. Avogadro’s number may be designated using the symbol L or NA. Note that Avogadro’s number, on its own, is a dimensionless quantity.
Azeotrope
An azeotrope is a mixture of liquids that maintains its composition and boiling point during distillation. It is also known as an azeotropic mixture or constant boiling point mixture. Azeotropy occurs when a mixture is boiled to produce a vapor that has the same composition as the liquid.
Azimuthal Quantum Number
The azimuthal quantum number, ℓ, is the quantum number associated with the angular momentum of an atomic electron. It is also known as the angular momentum quantum number or the second quantum number. The angular momentum quantum number determines the shape of the electron’s orbital. Arnold Sommerfeld proposed the azimuthal quantum number, based on the Bohr model of the atom.
argon
Argon is the name for the element with atomic number 18 and is represented by the symbol Ar. It is a member of the noble gases group.
B
Back Titration
A back titration is a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent. The remaining excess reagent is then titrated with another, second reagent. The second titration’s result shows how much of the excess reagent was used in the first titration, thus allowing the original analyte’s concentration to be calculated.
A back titration may also be called an indirect titration.
Balanced Equation
A balanced equation is an equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.
Balmer Series
The Balmer series is the portion of the emission spectrum of hydrogen that represents electron transitions from energy levels n > 2 to n = 2. These are four lines in the visible spectrum. They are also known as the Balmer lines.
Barometer
A barometer is a device that measures atmospheric pressure. The word “barometer” comes from the Greek words for “weight” and “measure.” Changes in atmospheric pressure recorded by barometers are most often used in meteorology for forecasting weather.
Base
In chemistry, a base is a chemical species that donates electrons, accepts protons, or releases hydroxide (OH-) ions in aqueous solution. Bases display certain characteristic properties that can be used to help identify them. They tend to be slippery to the touch (e.g., soap), can taste bitter, react with acids to form salts, and catalyze certain reactions. Types of bases include Arrhenius base, Bronsted-Lowry base, and Lewis base. Examples of bases include alkali metal hydroxides, alkaline earth metal hydroxides, and soap.
Base Metal
A base metal is any metal other than the noble metals or precious metals (gold, silver, platinum, etc.). Base metals typically tarnish or corrode readily. Such a metal will react with dilute hydrochloric acid to produce hydrogen gas. (Note: although copper does not react as easily with hydrochloric acid, it is still considered a base metal.) The base metals are “common” in that they are readily available and typically inexpensive. Although coins may be made from base metals, they typically are not the basis for currency.
Basic Solution
A basic solution is an aqueous solution containing more OH-ions than H+ions. In other words, it is an aqueous solution with a pH greater than 7. Basic solutions contain ions, conduct electricity, turn red litmus paper blue, and feel slippery to the touch.
Beer’s Law
Beer’s Law is an equation that relates the attenuation of light to properties of a material. The law states that the concentration of a chemical is directly proportional to the absorbance of a solution. The relation may be used to determine the concentration of a chemical species in a solution using a colorimeter or spectrophotometer. The relation is most often used in UV-visible absorption spectroscopy. Note that Beer’s Law is not valid at high solution concentrations.
Berkelium
Berkelium is one of the radioactive synthetic elements made in the cyclotron at Berkeley, California and the one that honors the work of this lab by bearing its name. It was the fifth transuranium element discovered (following neptunium, plutonium, curium, and americium). Here’s a collection of facts about element 97 or Bk, including its history and properties
Beryllium
Beryllium has a melting point of 1287+/-5°C, boiling point of 2970°C, specific gravity of 1.848 (20°C), and valence of 2. The metal is steel-gray in color, very light, with one of the highest melting points of the light metals. Its modulus of elasticity is a third higher than that of steel. Beryllium has high thermal conductivity, is nonmagnetic, and resists attack by concentrated nitric acid.
Beta Decay
Beta decay refers to the spontaneous radioactive decay where a beta particle is produced. There are two types of beta decay where the beta particle is either an electron or a positron.
Binary Acid
A binary acid is a binary compound where one element is hydrogen and the other is a nonmetal. Binary acids are also known as hydracids.
Binary Compound
A binary compound is a compound made up of two elements.
Binding Energy
In physics, binding energy is the minimum energy required to either separate an electron from an atom or to separate the protons and neutrons of an atomic nucleus. It is equal to the mass defect less the quantity of energy or mass released when a bound system is created. Binding energy is also known as separation energy.
Biochemistry
Biochemistry is the science in which chemistry is applied to the study of living organisms and the atoms and molecules which comprise living organisms. Take a closer look at what biochemistry is and why the science is important.
Bismuth
Bismuth is the name for the element with atomic number 83 and is represented by the symbol Bi. It is a member of the metal group.
Bitumen
Bitumen—also known as asphaltum or tar—is a black, oily, viscous form of petroleum, a naturally-occurring organic byproduct of decomposed plants. It is waterproof and flammable, and this remarkable natural substance has been used by humans for a wide variety of tasks and tools for at least the past 40,000 years. There are a number of processed types of bitumen used in the modern world, designed for paving streets and roofing houses, as well as additives to diesel or other gas oils.
Black Light
A black light is a type of lamp that emits primarily ultraviolet light and very little visible light. Because the light is outside the range of human vision, it is invisible, so a room illuminated with a black light appears dark.
Block Copolymer
A block copolymer is a copolymer formed when the two monomers cluster together and form ‘blocks’ of repeating units.
Boiling
Boiling is defined as a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point. At the boiling point, the vapor pressure of the liquid is the same as the external pressure acting upon its surface.
Also Known As: Two other words for boiling are ebullition and vaporization.
Boiling Point
The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid. Therefore, the boiling point of a liquid depends on atmospheric pressure. The boiling point becomes lower as the external pressure is reduced. As an example, at sea level the boiling point of water is 100 C (212 F), but at 6,600 feet the boiling point is 93.4 C (200.1 F).
Boiling Point Elevation
Boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure are examples of colligative properties. These are properties of matter that are affected by the number of particles in a sample.
Bond Dissociation Energy
Bond dissociation energy is defines as the amount of energy which is required to homolytically fracture a chemical bond. A homolytic fracture usually produces radical species. Shorthand notation for this energy is BDE, D0, or DH°. Bond dissociation energy is often used as a measure of the strength of a chemical bond and to compare different bonds. Note the enthalpy change is temperature dependent. Typical units of bond dissociation energy are kJ/mol or kcal/mol. Bond dissociation energy may be measured experimentally using spectrometry, calorimetry, and electrochemical methods.
Bond Energy
Bond energy (E) is defined as the amount of energy required to break apart a mole of molecules into its component atoms. It is a measure of the strength of a chemical bond. Bond energy is also known as bond enthalpy (H) or simply as bond strength.
Bond Enthalpy
Bond enthalpy is the enthalpy change when one mole of bonds are broken in a substance at 298 K. Bond enthalpy is also known as bond-dissociation enthalpy, bond strength, or average bond energy. The higher its value, the stronger the bond and the more energy required to break it.
Bond Length
In chemistry, bond length is the equilibrium distance between the nuclei of two groups or atoms that are bonded to each other. Bond length is a property of a chemical bond between types of atoms. Bonds vary between atoms depending on the molecule that contains them. For example the carbon-hydrogen bond is different in methyl chloride as is methane. When more electrons participate in a bond, it tends to be shorter. Bond lengths in solids are measured using x-ray diffraction. In gases, length may be approximated using microwave spectroscopy.
Bond Order
Bond order is a measurement of the number of electrons involved in bonds between two atoms in a molecule. It is used as an indicator of the stability of a chemical bond. Usually, the higher the bond order, the stronger the chemical bond.
Most of the time, bond order is equal to the number of bonds between two atoms. Exceptions occur when the molecule contains antibonding orbitals.
Bond order is calculated by the equation: Bond order = (number of bonding electrons – number of antibonding electrons)/2 If bond order = 0, the two atoms are not bonded. While a compound can have a bond order of zero, this value is not possible for elements.
Bonds
In chemistry, a bond or chemical bond is a link between atoms in molecules or compounds and between ions and molecules in crystals. A bond represents a lasting attraction between different atoms, molecules or ions.
Boron 
Atomic number: 5
Symbol: B
Atomic weight: 10.811
Electron configuration: [He]2s22p1
Word origin: Arabic Buraq; Persian Burah. These are the Arabic and Persian words for borax.
Isotopes: Natural boron is 19.78% boron-10 and 80.22% boron-11. B-10 and B-11 are the two stable isotopes of boron. Boron has a total of 11 known isotopes ranging from B-7 to B-17.
Boyle’s Law
Boyle’s law states that the pressure of an ideal gas increases as its container volume decreases. Chemist and physicist Robert Boyle published the law in 1662. The gas law is sometimes called Mariotte’s law or the Boyle-Mariotte law because French physicist Edme Mariotte independently discovered the same law in 1679.
Branched Chain Alkane
A branched chain alkane or branched alkane is an alkane which has alkyl groups bonded to its central carbon chain. Branched alkanes contain only carbon and hydrogen (C and H) atoms, with carbons connected to other carbons by single bonds only, but the molecules contain branches (methyl, ethyl, etc.) so they are not linear.
Brass
Brass is an alloy made primarily of copper and zinc. The proportions of the copper and zinc are varied to yield many different kinds of brass.
Bromine
Bromine is a halogen element with atomic number 35 and element symbol Br. At room temperature and pressure, it is one of the few liquid elements. Bromine is known for its brown color and characteristic acrid odor.
Bronsted-Lowry Acid
A Bronsted-Lowry acid is defined as a substance that gives up or donates hydrogen ions during a chemical reaction. In contrast, aBronsted-Lowry base accepts hydrogen ions. Another way of looking at it is that a Bronsted-Lowry acid donates protons, while the base accepts protons. Species that can either donate or accept protons, depending on the situation, are considered to be amphoteric.
Bronze
Bronze is one of the earliest metals known to man. It is defined as an alloy made of copper and another metal, usually tin. Compositions vary, but most modern bronze is 88% copper and 12% tin. Bronze may also contain manganese, aluminum, nickel, phosphorus, silicon, arsenic, or zinc.
Buffer
A buffer is a solution containing either a weak acid and its salt or a weak base and its salt, which is resistant to changes in pH. In other words, a buffer is an aqueous solution of either a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer may also be called a pH buffer, hydrogen ion buffer, or buffer solution.
C
Cadmium
Cadmium is the name for the element with atomic number 48 and is represented by the symbol Cd. It is a member of the transition metals group.
Caffeine
Caffeine (C8H10N4O2) is the common name for trimethylxanthine (systematic name is 1,3,7-trimethylxanthine or 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione). The chemical is also known as coffeine, theine, mateine, guaranine, or methyltheobromine. Caffeine is naturally produced by several plants, including coffee beans, guarana, yerba maté, cacao beans, and tea.
Calcium
Calcium is silver to gray solid metal that develops a pale yellow tint. It is element atomic number 20 on the periodic table with the symbol Ca. Unlike most transition metals, calcium and its compounds exhibit a low toxicity. The element is essential for human nutrition. Take a look at calcium periodic table facts and learn about the element’s history, uses, properties, and sources.
Calorie
A calorie is a unit of energy, but whether or not the “c” in the word is capitalized matters.
Calorie
A calorie is a unit of thermal energy equal to 4.184 joules or the amount of energy required to raise the temperature of 1 gram of liquid water 1°C at standard pressure. Sometimes a calorie (written with a lowercase “c”) is called a small calories or a gram calorie. The symbol for the calorie is cal.
Calorimeter
A calorimeter is a device used to measure the heat flow of a chemical reaction or physical change. The process of measuring this heat is called calorimetry. A basic calorimeter consists of a metal container of water above a combustion chamber, in which a thermometer is used to measure the change in water temperature. However, there are many types of more complex calorimeters.
Carbon
Carbon is the element with atomic number 6 on the periodic table with symbol C. This nonmetallic element is the key to the chemistry of living organisms, primarily due to its tetravalent state, which allows it to form four covalent chemical bonds with other atoms.
Carbonate
In chemistry, a carbonate is an ion consisting of one carbon and three oxygen atoms or a compound that contains this species as its anion. The molecular formula for the carbonate ion is CO32-
Carbonyl
The term carbonyl refers to the carbonyl functional group which is a divalent group consisting of a carbon atom with a double-bond to oxygen, C=O. Carbonyl also may refer to a compound formed by a metal with carbon monoxide (=CO). Bivalent radical CO is found in ketones, acids, and aldehydes. Many of the molecules involved in the senses of smell and taste involve aromatic compounds with carbonyl groups.
Carboxyl Group
In chemistry, the carboxyl group is an organic, functional group consisting of a carbon atom that’s double-bonded to an oxygen atom and singly bonded to a hydroxyl group. Another way to view it is as a carbonyl group (C=O) that has a hydroxyl group (O-H) attached to the carbon atom.
Catalysis
Catalysis is defined as increasing the rate of a chemical reaction by introducing a catalyst. A catalyst, in turn, is a substance that is not consumed by the chemical reaction, but acts to lower its activation energy. In other words, a catalyst is both a reactant and product of a chemical reaction. Typically, only a very small quantity of catalyst is required in order to catalyze a reaction.
Catenation
atenation is the binding of an element to itself through covalent bonds to form chain or ring molecules.
Cathode
The cathode is the electrode from which electrical current departs. The other electrode is named the anode. Keep in mind, the conventional definition of current describes the direction a positive electric charge moves, while most of the time electrons are true current carries. This can be confusing, so the mnenomic CCD for cathode current departs may help reinforce the definition. Usually, current departs in the direction opposite electron movement.
Cathode Ray Tube
A cathode is a terminal or electrode at which electrons enter a system, such as an electrolytic cell or an electron tube.
Cation
A cation is an ionic species with a positive charge. The word “cation” comes from the Greek word “kato,” which means “down.” A cation has more protons than electrons, giving it a net positive charge.
Celsius Temperature Scale
The Celsius temperature scale is a common System Internationale (SI) temperature scale (the official scale is Kelvin). The Celsius scale is based on a derived unit defined by assigning the temperatures of 0°C and 100°C to the freezing and boiling points of water, respectively, at 1 atm pressure. More precisely, the Celsius scale is defined by absolute zero and the triple point of pure water. This definition allows easy conversion between the Celsius and Kelvin temperature scales, such that absolute zero is defined to be precisely 0 K and −273.15 °C. The triple point of water is defined to be 273.16 K (0.01 °C; 32.02 °F). The interval between one degree Celsius and one Kelvin are exactly the same. Note the degree is not used in the Kelvin scale because it is an absolute scale.
Cerium
Cerium (Ce) is atomic number 58 on the periodic table. Like other lanthanides or rare earth elements, cerium is a soft, silver-colored metal. It’s the most abundant of the rare earth elements.
Cesium
Cesium or caesium is a metal with the element symbol Cs and atomic number 55. This chemical element is distinctive for several reasons.
Chain Reaction
chain reaction is a series of reactions where the products contribute to the reactants of another reaction without outside influence.
Charge
Charge usually refers to electric charge, which is a conserved property of certain subatomic particles that determines their electromagnetic interaction. Charge is a physical property that causes matter to experience a force within an electromagnetic field. Electric charges may be positive or negative in nature.
cetane number (CN)
cetane number (CN) – value that describes the combustion quality of diesel fuel, based on the delay between injection and ignition.
D
DNA
DNA is the acronym for deoxyribonucleic acid, usually 2′-deoxy-5′-ribonucleic acid. DNA is a molecular code used within cells to form proteins. DNA is considered a genetic blueprint for an organism because every cell in the body that contains DNA has these instructions, which enable the organism to grow, repair itself, and reproduce.
Dalton’s Law
Dalton’s Law of Partial Pressures, or Dalton’s Law, states that the total pressure of a gas in a container is the sum of the partial pressures of the individual gases in the container. Here is a worked example problem showing how to use Dalton’s Law to calculate the pressure of a gas.
Dehydration Reaction
A dehydration reaction is a chemical reaction between two compounds where one of the products is water. For example, two monomers may react where a hydrogen (H) from one monomer binds to a hydroxyl group (OH) from the other monomer to form a dimer and a water molecule (H2O). The hydroxyl group is a poor leaving group, so Bronsted acid catalysts may be used to help to protonate the hydroxyl to form -OH2+. The reverse reaction, where water combines with hydroxyl groups, is termed hydrolysis or a hydration reaction.
Density
A material’s density is defined as its mass per unit volume. Put another way, density is the ratio between mass and volume or mass per unit volume. It is a measure of how much “stuff” an object has in a unit volume (cubic meter or cubic centimeter). Density is essentially a measurement of how tightly matter is crammed together.
Detergent
A detergent is a surfactant or mixture of surfactants that has cleaning properties in dilute solution with water.
Diffusion
Diffusion is the movement of a fluid from an area of higher concentration to an area of lower concentration. Diffusion is a result of the kinetic properties of particles of matter.
Dipole
A dipole is a separation of opposite electrical charges. A dipole is quantified by its dipole moment (μ).
There are two types of dipoles:
Electric dipoles
Magnetic dipoles
Dipole Moment
A dipole moment is a measurement of the separation of two opposite electrical charges. Dipole moments are a vector quantity. The magnitude is equal to the charge multiplied by the distance between the charges and the direction is from negative charge to positive charge.
Dissolve
In chemistry, to dissolve is to cause a solute to pass into a solution. Dissolving is also called dissolution. Typically, this involves a solid going into a liquid phase, but dissolution can involve other transformations as well. For example, when alloys form, one solid dissolves into another to form a solid solution.
Double Bond
A double bond is a type of chemical bond in which two electron pairs are shared between two atoms. This type of bond involves four bonding electrons between atoms, rather than the usual two bonding electrons involved in a single bond. Because of the large number of electrons, double bonds tend to be reactive. Double bonds are shorter and stronger than single bonds.
E
Effective Nuclear Charge
The effective nuclear charge is the net charge an electron experiences in an atom with multiple electrons.
Elasticity
Elasticity is a physical property of a material whereby the material returns to its original shape after having been stretched out or altered by force. Substances that display a high degree of elasticity are termed “elastic.” The SI unit applied to elasticity is the pascal (Pa), which is used to measure the modulus of deformation and elastic limit.
Electrical Conductivity
Electrical conductivity is the measure of the amount of electrical current a material can carry or it’s ability to carry a current. Electrical conductivity is also known as specific conductance. Conductivity is an intrinsic property of a material.
Electrochemical Cell
An electrochemical cell is a device that generates a potential difference between electrodes using chemical reactions. Galvanic cells and electrolytic cells are examples of electrochemical cells.
Electrolysis
Electrolysis is the passage of a direct electric current through an ion-containing solution to drive a non-spontaneous chemical reaction. Electrolysis produces chemical changes at the electrodes.
Electromagnetic Radiation
Electromagnetic radiation is self-sustaining energy with electric and magnetic field components. Electromagnetic radiation is commonly referred to as “light”, EM, EMR, or electromagnetic waves.
Electron
An electron is a stable negatively charged component of an atom. Electrons exist outside of and surrounding the atom nucleus. Each electron carries one unit of negative charge (1.602 x 10-19 coulomb) and has a small mass as compared with that of a neutron or proton.
Electron Density
Electron density is a representation of the probability of finding an electron in a specific location around an atom or molecule. In general, the electron is more likely to be found in regions with high electron density.
Electronegativity
Electronegativity is the property of an atom which increases with its tendency to attract the electrons of a bond. If two bonded atoms have the same electronegativity values as each other, they share electrons equally in a covalent bond.
Element
A chemical element is a substance that cannot be broken down by chemical means. Although elements aren’t changed by chemical reactions, new elements may be formed by nuclear reactions.
Energy 
Energy is defined as the capacity of a physical system to perform work. However, it’s important to keep in mind that just because energy exists, that doesn’t mean it’s necessarily available to do work.
F
Fatty Acid
A fatty acid is a carboxylic acid with a long side chain of hydrocarbons. Most fatty acids contain an even number of carbon atoms in the hydrocarbon chain.
Fire Point
Fire point is the lowest temperature where the vapor of a liquid will initiate and sustain a combustion reaction. By definition, the fuel must continue to burn for at least 5 seconds following ignition by an open flame for the temperature to be considered the fire point.
Fission
Fission is the splitting of an atomic nucleus into two or more lighter nuclei accompanied by energy release. The original heavy atom is termed the parent nucleus, and the lighter nuclei are daughter nuclei. Fission is a type of nuclear reaction that may occur spontaneously or as a result of a particle striking an atomic nucleus.
Fluid
A fluid is any substance that flows or deforms under applied shear stress. Fluids comprise a subset of the states of matter and include liquids, gases, and plasma.
Foam
A foam is a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets.
Force
In science, force is the push or pull on an object with mass that causes it to change velocity (to accelerate). Force represents as a vector, which means it has both magnitude and direction.
Formal Charge
Formal charge of FC is the difference between the number of valence electrons of each atom and the number of electrons the atom is associated with. Formal charge assumes any shared electrons are equally shared between the two bonded atoms.
Formula Mass
The formula mass of a molecule (also known as formula weight) is the sum of the atomic weights of the atoms in the empirical formula of the compound. Formula weight is given in atomic mass units (amu).
Freezing Point
The freezing point is the temperature at which a liquid changes to a solid. The freezing point of a substance is not necessarily the same as its melting point.
Frequency
In the most general sense, frequency is defined as the number of times an event occurs per unit of time. In physics and chemistry, the term frequency is most often applied to waves, including light, sound, and radio. Frequency is the number of times a point on a wave passes a fixed reference point in one second.
G
Gallium
Gallium is a bright blue-silver metal with a melting point low enough you can melt a chunk in your hand. Here are interesting facts about this element.
Gamma Radiation
Gamma radiation or gamma rays are high-energy photons that are emitted by radioactive decay of atomic nuclei. Gamma radiation is very high-energy form of ionizing radiation, with the shortest wavelength.
Gas
A gas is defined as a state of matter consisting of particles that have neither a defined volume nor defined shape. It is one of the four fundamental states of matter, along with solids, liquids, and plasma.
Gas Constant
Chemistry and physics equations commonly include “R”, which is the symbol for the gas constant, molar gas constant, ideal gas constant, or universal gas constant. It is a proportionality factor that relates energy scales and temperature scales in several equations.
Gay-Lussac’s Law
Gay-Lussac’s law is an ideal gas law which states that at constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature (in Kelvin).
Geometric Isomer
Geometric isomers are chemical species with the same type and quantity of atoms as one another, yet having different geometric structures. In geometric isomers, atoms or groups exhibit different spatial arrangements on either side of a chemical bond or ring structure. Geometric isomerism is also called configurational isomerism or cis-trans isomerism.
Germanium
Gemanium is a shiny grayish-white metalloid with a metallic appearance. The element is best known for its use in semiconductors. Here is a collection of useful and interesting germanium element facts.
Glass
Glass is an amorphous solid. The term is usually applied to inorganic solids and not to plastics or other organics. Glasses do not have crystalline internal structure. They usually are hard and brittle solids.
Glycosidic Bond
A glycosidic bond is a covalent bond that joins a carbohydrate to another functional group or molecule. A substance containing a glycosidic bond is termed a glycoside. Glycosides may be categorized according to elements involved in the chemical bond.
Gold
Gold is an element that was known to ancient man and has always been prized for its color. It was used as jewelry in prehistoric times, alchemists spent their lives trying to transmute other metals into gold, and it is still one of the most prized metals.
Gram
A gram is a unit of mass in the metric system defined as one thousandth (1 x 10-3) of a kilogram. Originally, the gram was defined as a unit equal to the mass of one cubic centimeter of pure water at 4°C
H
Haber Process
The Haber process or Haber-Bosch process is the primary industrial method used to make ammonia or fix nitrogen. The Haber process reacts nitrogen and hydrogen gas to form ammonia.
Hafnium
Hafnium is an element that was predicted by Mendeleev (of periodic table fame) before it was actually discovered. Here is a collection of fun and interesting facts about hafnium, as well as standard atomic data for the element.
Halogenated Hydrocarbon
A halogenated hydrocarbon is a hydrocarbon that contains one or more halogen atoms. The chemical compound is also known as a halocarbon.
Halogens
The halogen elements are located in group 17 or VIIA of the periodic table, which is the second-to-last column of the chart. This is a list of elements that belong to the halogen group and a look at the properties that they share in common.
Hard Water
Hard water is water that contains high amounts of Ca2+ and/or Mg2+. Sometimes Mn2+ and other multivalent cations are included in the measure of hardness. Note water may contain minerals and yet not be considered hard, by this definition. Hard water occurs naturally under the condition where water percolates through calcium carbonates or magnesium carbonates, such as chalk or limestone.
Hassium
Element atomic number 108 is hassium, which has the element symbol Hs. Hassium is one of the manmade or synthetic radioactive elements. Only about 100 atoms of this element have been produced so there is not a lot of experimental data for it. Properties are predicted based on the behavior of other elements in the same element group. Hassium is expected to be a metallic silver or gray metal at room temperature, much like the element osmium.
Heat Capacity
Heat capacity is the amount of heat energy required to raise the temperature of a body a specified amount. In SI units, heat capacity (symbol: C) is the amount of heat in joules required to raise the temperature 1 Kelvin.
Heat Energy
Most people use the word heat to describe something that feels warm, however in science, thermodynamic equations, in particular, heat is defined as the flow of energy between two systems by means of kinetic energy.
Heavy Metal
A heavy metal is a dense metal that is (usually) toxic at low concentrations. Although the phrase “heavy metal” is common, there is no standard definition assigning metals as heavy metals.
Helium
Helium is atomic number 2 on the periodic table, with the element symbol He. It is a colorless, flavorless gas, best known for its use in filling floating balloons. Here is a collection of facts about this lightweight, interesting element
Henry’s Law
Henry’s Law is a chemistry law which states that the mass of a gas which will dissolve into a solution is directly proportional to the partial pressure of that gas above the solution.
I
Ideal Gas Law
The ideal gas law is also known as the general gas equation. It is an equation of state of an ideal gas that relates pressure, volume, quantity of gas, and temperature. While the law describes the behavior of a hypothetical gas, it approximates the behavior of real gases in many situations.
Indicator
A chemical indicator is a substance that undergoes a distinct observable change when conditions in its solution change. This could be a color change, precipitate formation, bubble formation, temperature change, or other measurable quality.
Indium
Indium is a chemical element with atomic number 49 and element symbol In. It is a silvery-white metal that most closely resembles tin in appearance. However, it is chemically more similar to gallium and thallium. Except for the alkali metals, indium is the softest metal.
Inductive Effect
The inductive effect, sometimes written as “the -I Effect” in literature, is the distance-dependent phenomenon by which the charge of a chemical bond affects orientation on adjacent bonds in a molecule, producing a permanent state of polarization.
Inorganic Chemistry
Inorganic chemistry is defined as the study of the chemistry of materials from non-biological origins. Typically, this refers to materials not containing carbon-hydrogen bonds, including metals, salts, and minerals. Inorganic chemistry is used to study and develop catalysts, coatings, fuels, surfactants, materials, superconductors, and drugs. Important chemical reactions in inorganic chemistry include double displacement reactions, acid-base reactions, and redox reactions.Inorganic chemistry is defined as the study of the chemistry of materials from non-biological origins. Typically, this refers to materials not containing carbon-hydrogen bonds, including metals, salts, and minerals. Inorganic chemistry is used to study and develop catalysts, coatings, fuels, surfactants, materials, superconductors, and drugs. Important chemical reactions in inorganic chemistry include double displacement reactions, acid-base reactions, and redox reactions.
Insoluble
Insoluble means incapable of dissolving in a solvent. It is rare for absolutely no solute to dissolve at all. However, many substances are poorly soluble.
Intensive Property
An intensive property is a property of matter that does not change as the amount of matter changes. It is a bulk property, which means it is a physical property that is not dependent on the size or mass of a sample.
Intermediate
An intermediate or reaction intermediate is a substance formed during a middle step of a chemical reaction between reactants and the desired product. Intermediates tend to be extremely reactive and short-lived, so they represent a low concentration in a chemical reaction compared with the amount of reactants or products.
Intermolecular Force
The intermolecular force is the sum of all the forces between two neighboring molecules. The forces result from the actions of the kinetic energy of atoms and the slight positive and negative electrical charges on different parts of a molecule that affect its neighbors and any solute that may be present.
Inverse Proportion
Inverse proportion is the relationship between two variables when their product is equal to a constant value. When the value of one variable increases, the other decreases, so their product is unchanged.
Iodine
Iodine is the name for the element with atomic number 53 and is represented by the symbol I. It is a member of the halogen group.
Ion
An ion is defined as an atom or molecule that has gained or lost one or more of its valence electrons, giving it a net positive or negative electrical charge. In other words, there is an imbalance in the number of protons (positively charged particles) and electrons (negatively charged particles) in a chemical species.
J
Joule
The joule (symbol: J) is the basic SI unit of energy. A joule is equal to the kinetic energy of a kilogram mass moving at the speed of one meter per second
K
Kelvin Temperature Scale
The Kelvin temperature scale is an absolute temperature scale with zero at absolute zero. Because it is an absolute scale, measurements made using the Kelvin scale do not have degrees. The kelvin (note the lowercase letter) is the base unit of temperature in the International System of Units (SI).
Keratin
Keratin is a fibrous structural protein found in animal cells and used to form specialized tissues. Specifically, the proteins are only produced by chordates (vertebrates, Amphioxus, and urochordates), which includes mammals, birds, fish, reptiles, and amphibians. The tough protein protects epithelial cells and strengthens certain organs. The only other biological material possessing similar toughness is the protein chitin, found in invertebrates (e.g., crabs, cockroaches).
Ketone
A ketone is a compound containing a carbonyl functional group bridging two groups of atoms. The general formula for a ketone is RC(=O)R’ where R and R’ are alkyl or aryl groups. IUPAC ketone functional group names contain “oxo” or “keto”. Ketones are named by changing the -e on the end of the parent alkane name to -one.
Kilopascal
The kilopascal is a unit of pressure. 1 kPa is approximately the pressure exerted by a 10-g mass resting on a 1-cm2 area. 101.3 kPa = 1 atm. There are 1,000 pascals in 1 kilopascal. The pascal and thus the kilopascal are named for the French polymath Blaise Pascal.
Kinetic Energy
Kinetic energy is the energy an object possesses due to its motion. An object of mass m moving at velocity v has a kinetic energy equal to ½mv2.
Krypton
Element 36 on the periodic table with symbol Kr.
L
Lanthanides
The lanthanides are generally considered to be elements with atomic numbers 58-71 (lanthanum to lutetium). The lanthanide series is the group of elements in which the 4f sublevel is being filled. All of these elements are metals (specifically, transition metals). They share several common properties.
Lanthanum
Lanthanum is element number 57 with element symbol La. It is a soft, silver-colored, ductile metal known as the starting element for the lanthanide series. It is a rare earth element that usually displays the oxidation number of +3. While lanthanum serves no known biological role in humans and other animals, it is an essential element for some types of bacteria.
Law of Chemical Equilibrium
The Law of Chemical Equilibrium is a relation stating that in a reaction mixture at equilibrium, there is a condition (given by the equilibrium constant, Kc) relating the concentrations of the reactants and products.
Law of Combining
In chemistry, the law of combining volumes is a relation stating that the relative volumes of gases in a chemical reaction are present in the ratio of small integers (assuming all gases are at the same temperature and pressure)
Law of Conservation of Energy
The law of conservation of energy is a physical law that states energy cannot be created or destroyed but may be changed from one form to another. Another way of stating this law of chemistry is to say the total energy of an isolated system remains constant or is conserved within a given frame of reference.
Law of Conservation of Mass
In the context of the study of chemistry, the law of conservation of mass says that in a chemical reaction, the mass of the products equals the mass of the reactants.
Law of Constant Composition
law of constant composition (also known as the law of definite proportions) states that samples of a pure compound always contain the same elements in the same mass proportion. This law, together with the law of multiple proportions, is the basis for stoichiometry in chemistry.
Lead
Lead is a heavy metallic element, commonly encountered in radiation shielding and soft alloys. It is a dull gray metal with element symbol Pb and atomic number 82. Here’s a collection of interesting facts about lead, including about its properties, uses, and sources.
Ligand
A ligand is an atom, ion, or molecule that donates or shares one or more of its electrons through a covalent bond with a central atom or ion. It is a complexing group in coordination chemistry that stabilizes the central atom and determines its reactivity. Ligands are usually considered to be Lewis bases, although a few cases of Lewis acid ligands exist.
Liquid
A liquid is one of the states of matter. The particles in a liquid are free to flow, so while a liquid has a definite volume, it does not have a definite shape. Liquids consist of atoms or molecules that are connected by intermolecular bonds.
Lithium
Alkali metal with atomic number 3 and element symbol Li.
Lone Pair
A lone pair is an electron pair in the outermost shell of an atom that is not shared or bonded to another atom. It is also called a non-bonding pair. One way to identify a lone pair is to draw a Lewis structure. The number of lone pair electrons added to the number of bonding electrons equals the number of valence electrons of an atom.
M
Macromolecule
In chemistry and biology, a macromolecule is defined as a molecule with a very large number of atoms. Macromolecules typically have more than 100 component atoms. Macromolecules exhibit very different properties from smaller molecules, including their subunits, when applicable.
Magnesium
Magnesium is an element that is essential for human nutrition. This alkaline earth metal has atomic number 12 and element symbol Mg. The pure element is a silver-colored metal, but it tarnishes in air to give it a dull appearance.
Mass
Mass is a property that reflects the quantity of matter within a sample. Mass usually is reported in grams (g) and kilograms (kg).
Mass Number
Mass number is an integer (whole number) equal to the sum of the number of protons and neutrons of an atomic nucleus. In other words, it is the sum of the number of nucleons in an atom. Mass number is often denoted using a capital letter A.
Mass Percentage
Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture. Mass percentage is calculated as the mass of a component divided by the total mass of the mixture, multiplied by 100%.
Measurement
In science, a measurement is a collection of quantitative or numerical data that describes a property of an object or event. A measurement is made by comparing a quantity with a standard unit. Since this comparison cannot be perfect, measurements inherently include error, which is how much a measured value deviates from the true value. The study of measurement is called metrology.
Meitnerium
Meitnerium (Mt) is element 109 on the periodic table. It’s one of the few elements that suffered no dispute concerning its discovery or name. Here is a collection of interesting Mt facts, including the element’s history, properties, uses, and atomic data.
Melting PointMelting Point
The melting point of a substance is the temperature at which a solid and liquid phase may coexist in equilibrium and the temperature at which matter changes from solid to liquid form. The term applies to pure liquids and solutions. Melting point depends on pressure, so it should be specified. Typically, tables of melting points are for standard pressure, such as 100 kPa or 1 atmosphere. Melting point may also be called the liquefaction point.
Mercury
Mercury is the only metallic element that is a liquid at room temperature. This dense metal is atomic number 80 with element symbol Hg. This collection of mercury facts includes atomic data, the electron configuration, chemical and physical properties, and history of the element.
Metabolism
Metabolism is the set of biochemical reactions involved in storing fuel molecules and converting fuel molecules into energy. Metabolism may also refer to the sequence of biochemical reactions compounds undergo inside a living cell. The word “metabolism” comes from the Greek word metabolē, which means “change.”
Metal
The definition of metal: A substance with high electrical conductivity, luster, and malleability, which readily loses electrons to form positive ions (cations). Metals are otherwise defined according to their position on the Periodic Table.
Metallic Character
Metallic character describes the set of chemical properties that are associated with the elements classified as metals in the periodic table. Metallic character depends on the ability of an element to lose its outer valence electrons.
Metallic Compounds
A metallic compound is a compound that contains one or more metal elements bonded to another element. Typically, the metal atom acts as the cation in the compound and is bonded to a nonmetallic anion or an ionic group. Because it has a positive charge, the metal element symbol is listed first in the chemical formula.
Metalloids
Between the metals and nonmetals is a group of elements known as either the semimetals or the metalloids, which are elements that have properties intermediate between those of the metals and nonmetals. Most metalloids have a shiny, metallic appearance but are brittle, unexceptional electrical conductors and display nonmetallic chemical properties. Metalloids have semiconductor properties and form amphoteric oxides.
Methyl Group
A methyl group is a functional group derived from methane containing one carbon atom bonded to three hydrogen atoms, -CH3. In chemical formulas, it may be abbreviated as Me. While the methyl group is commonly found in larger organic molecules, methyl may exist on its own as an anion( CH3), cation (CH3+), or radical (CH3). However, methyl on its own is extremely reactive. The methyl group in a compound is typically the most stable functional group in the molecule.
Micron Definition
A micron is a unit of length equivalent to a millionth of a meter. 1 micron = 1 μm = 10-6 m
Mixture
In chemistry, a mixture forms when two or more substances are combined such that each substance retains its own chemical identity. Chemical bonds between the components are neither broken nor formed. Note that even though the chemical properties of the components haven’t changed, a mixture may exhibit new physical properties, like boiling point and melting point.
Molality
Molality (m) and molarity (M) both express the concentration of a chemical solution. Molality is the number of moles of solute per kilogram of solvent. Molarity is the number of moles of solute per liter of solution. 
N
Neon
Neon is the element best-known for brightly-lit signs, but this noble gas is used for many other purposes.
Neutralization
A neutralization reaction is a chemical reaction between an acid and a base which produces a more neutral solution (closer to a pH of 7). The final pH depends on the strength of the acid and base in the reaction. At the end of a neutralization reaction in water, no excess hydrogen or hydroxide ions remain.
Neutralization reaction
A neutralization reaction is a chemical reaction between an acid and a base which produces a more neutral solution (closer to a pH of 7). The final pH depends on the strength of the acid and base in the reaction. At the end of a neutralization reaction in water, no excess hydrogen or hydroxide ions remain.
Neutron
The neutron is the particle in the atomic nucleus with a mass = 1 and charge = 0. Neutrons are found together with protons in the atomic nucleus. The number of neutrons in an atom determines its isotope.
Neutron
The neutron is the particle in the atomic nucleus with a mass = 1 and charge = 0. Neutrons are found together with protons in the atomic nucleus. The number of neutrons in an atom determines its isotope.
Newton
A newton is the SI unit of force. It is named in honor of Sir Isaac Newton, the English mathematician and physicist who developed laws of classical mechanics.
Niobium 
Niobium, like tantalum, can act as an electrolytic valve allowing alternating current to pass in only one direction through an electrolytic cell. Niobium is used in arc-welding rods for stabilized grades of stainless steel.
Nitrogen
Nitrogen (Azote) is an important nonmetal and the most abundant gas in the Earth’s atmosphere.
Noble Gases
The right column of the periodic table contains seven elements known as the inert or noble gases.
Nonelectrolyte
A nonelectrolyte is a substance that does not exist in an ionic form in aqueous solution. Nonelectrolytes tend to be poor electrical conductors and don’t readily dissociate into ions when melted or dissolved. Solutions of nonelectrolytes do not conduct electricity.
Nonoxidizing Acid
A nonoxidizing acid is an acid that cannot act as an oxidizing agent. While many acids are good oxidizers, they don’t all technically oxidize in any given reaction.
Nonpolar Molecule
A nonpolar molecule has no separation of charge, so no positive or negative poles are formed. In other words, the electrical charges of nonpolar molecules are evenly distributed across the molecule. Nonpolar molecules tend to dissolve well in nonpolar solvents, which are frequently organic solvents.
Nonvolatile
In chemistry, the term nonvolatile refers to a substance that does not readily evaporate into gas under existing conditions. In other words, a nonvolatile material exerts a low vapor pressure and has a slow rate of evaporation.
network solid
A network solid is a substance made up of an array of repeating covalently bonded atoms. Network solids are also known as covalent network solids. Because of the way atoms are arranged, a network solid may be considered a type of macromolecule. Network solids may be either crystals or amorphous solids.
O
Octane Number
The octane number seen on pumps at gasoline stations is a value used to indicate the resistance of a motor fuel to knock—that is, to make pinging or ticking sounds in a car’s engine when you step on the gas pedal.
Orbital
In chemistry and quantum mechanics, an orbital is a mathematical function that describes the wave-like behavior of an electron, electron pair, or (less commonly) nucleons. An orbital may also be called an atomic orbital or electron orbital. Although most people think of an “orbit” regarding a circle, the probability density regions that may contain an electron may be spherical, dumbbell-shaped, or more complicated three-dimensional forms.
Organic Chemistry
Organic chemistry is the study of carbon and the study of the chemistry of life. Since not all carbon reactions are organic, another way to look at organic chemistry would be to consider it the study of molecules containing the carbon-hydrogen (C-H) bond and their reactions.
Osmium
Osmium is an extremely heavy silver-blue metal with atomic number 76 and element symbol Os. While most elements aren’t know for the way they smell, osmium emits a characteristic unpleasant smell. The element and its compounds are highly toxic. Here is a collection of osmium element facts, including its atomic data, chemical and physical properties, uses, and sources.
Osmosis
Osmosis is the process where solvent molecules move through a semipermeable membrane from a dilute solution into a more concentrated solution (which becomes more dilute). In most cases, the solvent is water. However, the solvent may be another liquid or even a gas. Osmosis can be made to do work.
Oxidant
An oxidant is a reactant that oxidizes or removes electrons from other reactants during a redox reaction. An oxidant may also be called an oxidizer or oxidizing agent. When the oxidant includes oxygen, it may be called an oxygenation reagent or oxygen-atom transfer (OT) agent.
Oxidation
Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Oxidation occurs when the oxidation state of a molecule, atom or ion is increased. The opposite process is called reduction, which occurs when there is a gain of electrons or the oxidation state of an atom, molecule, or ion decreases.
Oxidation Numbers
Electrochemical reactions involve the transfer of electrons. Mass and charge are conserved when balancing these reactions, but you need to know which atoms are oxidized and which atoms are reduced during the reaction. Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom.
Oxidation State
Oxidation state and oxidation number are quantities that commonly equal the same value for atoms in a molecule and are often used interchangeably. Most of the time, it doesn’t matter if the term oxidation state or oxidation number is used. There is a slight difference between the two terms.
Oxide
An oxide is an ion of oxygen with oxidation state equal to -2 or O2-. Any chemical compound that contains O2- as its anion is also termed an oxide. Some people more loosely apply the term to refer to any compound where oxygen serves as the anion.
P
PH
pH is a measure of hydrogen ion concentration, a measure of the acidity or alkalinity of a solution. The pH scale usually ranges from 0 to 14.
PH Indicator
A pH indicator or acid-base indicator is a compound that changes color in solution over a narrow range of pH values. Only a small amount of indicator compound is needed to produce a visible color change.
Palladium
Palladium is a silvery-white metallic element with atomic number 46 and element symbol Pd. In daily life, it’s most often found in jewelry, dentistry, and catalytic converters for automobiles.
Paramagnetism
Paramagnetism refers to a property of certain materials that are weakly attracted to magnetic fields. When exposed to an external magnetic field, internal induced magnetic fields form in these materials that are ordered in the same direction as the applied field. Once the applied field is removed, the materials lose their magnetism as thermal motion randomizes the electron spin orientations.
Parent Nuclide
A parent nuclide is a nuclide that decays into a specific daughter nuclide during radioactive decay. A parent nuclide is also known as a parent isotope.
Partial Pressure
In a mixture of gases, each gas contributes to the total pressure of the mixture. This contribution is the partial pressure. The partial pressure is the pressure the gas if the gas were in the same volume and temperature by itself. Dalton’s law states the total pressure of a mixture of ideal gases is the sum of the partial pressure of each individual gas.
Parts Per Million
Parts per million (ppm) is a commonly used unit of concentration for small values. One part per million is one part of solute per one million parts solvent or 10-6. Parts per million and other “parts per” notations (e.g., parts per billion or parts per trillion) are dimensionless quantities with no units. Preferred methods for expressing parts per million include µV/V (microvolume per volume), µL/L (microliters per liter), mg/kg (milligram per kilogram), µmol/mol (micromole per mole), and µm/m (micrometer per meter).
Pauli Exclusion Principle
The Pauli exclusion principle states no two electrons (or other fermions) can have the identical quantum mechanical state in the same atom or molecule. In other words, no pair of electrons in an atom can have the same electronic quantum numbers n, l, ml, and ms. Another way to state the Pauli exclusion principle is to say the total wave function for two identical fermions is antisymmetric if the particles are exchanged.
Percent Composition
Percent composition is the percentage by mass of each element in a compound.
Percent Yield
Percent yield is the percent ratio of actual yield to the theoretical yield. It is calculated to be the experimental yield divided by theoretical yield multiplied by 100%.
Period
the term period refers to a horizontal row of the periodic table. Elements in the same period all have the same highest unexcited electron energy level or same ground state energy level. In other words, each atom has the same number of electron shells.
Periodic Law
The Periodic Law states that the physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number. Many of the properties recur at intervals. When the elements are arranged correctly, the trends in element properties become apparent and can be used to make predictions about unknown or unfamiliar elements, simply based on their placement on the table.
Periodic Table
The periodic table is a tabular arrangement of the chemical elements by increasing atomic number which displays the elements so that one may see trends in their properties. The Russian scientist Dmitri Mendeleev is most often credited with inventing the periodic table (1869). The modern table is derived from Mendeleev’s periodic table, but with one significant different. Mendeleev’s table ordered the elements according to increasing atomic weight rather than atomic number. However, his table illustrated recurring trends or periodicity in the element properties.
Petroleum
Petroleum or crude oil is any naturally-occurring flammable mixture of hydrocarbons found in geologic formations, such as rock strata. Most petroleum is a fossil fuel, formed from the action of intense pressure and heat on buried dead zooplankton and algae. Technically, the term petroleum only refers to crude oil, but sometimes it is applied to describe any solid, liquid or gaseous hydrocarbons.
Phase
In chemistry and physics, a phase is a physically distinctive form of matter, such as a solid, liquid, gas, or plasma.
Phosphorus
Phosphorus is a reactive nonmetal with element symbol P and atomic number 15. It is one of the essential elements in the human body and is widely encountered in products such as fertilizers, pesticides, and detergents. Learn more about this important element.
Photon
A photon is a discrete packet of energy associated with electromagnetic radiation (light). A photon has energy E which is proportional to the frequency ν of the radiation: E = hν, where h is Planck’s constant.
Physical Changes
A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The size or shape of matter may be changed, but no chemical reaction occurs.
Physical Changes
A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The size or shape of matter may be changed, but no chemical reaction occurs.
Physical Property
A physical property is a characteristic of matter that can be observed and measured without changing the chemical identity of the sample. The measurement of a physical property can change the arrangement of matter in a sample but not the structure of its molecules. In other words, a physical property might involve a physical change but not a chemical change. If a chemical change or reaction occurs, the observed characteristics are chemical properties.
Plasma
Plasma is a state of matter where the gas phase is energized until atomic electrons are no longer associated with any particular atomic nucleus. Plasmas are made up of positively charged ions and unbound electrons. Plasma may be produced by either heating a gas until it is ionized or by subjecting it to a strong electromagnetic field.
Q
Qualitative Analysis
In chemistry, qualitative analysis is the determination of the chemical composition of a sample. It encompasses a set of analytical chemistry techniques that provide nonnumerical information about a specimen.
Quantitative Analysis
Quantitative analysis refers to the determination of how much of a given component is present in a sample. The quantity may be expressed in terms of mass, concentration, or relative abundance of one or all components of a sample.
Quantum
In physics and chemistry, a quantum is a discrete packet of energy or matter. The term quantum also means the minimum value of a physical property involved in an interaction. The plural of quantum is quanta.
Quantum Number
A quantum number is a value that is used when describing the energy levels available to atoms and molecules. An electron in an atom or ion has four quantum numbers to describe its state and yield solutions to the Schrödinger wave equation for the hydrogen atom.
R
Radiation
Radiation and radioactivity are two easily confused concepts. Just remember, a substance does not need to be radioactive to emit radiation. Let’s look at the definition of radiation and see how it differs from radioactivity.
Radiation 
Radiation is the emission and propagation of energy in the form of waves, rays or particles.
Radioactivity
Radioactivity is the spontaneous emission of radiation in the form of particles or high energy photons resulting from a nuclear reaction. It is also known as radioactive decay, nuclear decay, nuclear disintegration, or radioactive disintegration. While there are many forms of electromagnetic radiation, they are not always produced by radioactivity. For example, a light bulb may emit radiation in the forms of heat and light, yet it is not radioactive. A substance that contains unstable atomic nuclei is considered to be radioactive.
Radium
Radium is the name for the element with atomic number 88 and is represented by the symbol Ra. It is a member of the alkaline earth metals group.
Raoult’s Law
Raoult’s law is a chemical law that states that the vapor pressure of a solution is dependent on the mole fraction of a solute added to the solution.
Reaction
A reaction or chemical reaction is a chemical change which forms new substances. In other words, reactants react to form products that have a different chemical formula. Indications a reaction has occurred include temperature change, color change, bubble formation, and/or precipitate formation.
Reactivity Series
The reactivity series is a list of metals ranked in order of decreasing reactivity, which is usually determined by the ability to displace hydrogen gas from water and acid solutions. It can be used to predict which metals will displace other metals in aqueous solutions in double displacement reactions and to extract metals from mixtures and ores. The reactivity series is also known as the activity series.
Reagent
A reagent is a compound or mixture added to a system to cause a chemical reaction or test if a reaction occurs. A reagent may be used to find out whether or not a specific chemical substance is present by causing a reaction to occur with it.
Real Gas
A real gas is a gas that does not behave as an ideal gas due to interactions between gas molecules. A real gas is also known as a nonideal gas because the behavior of a real gas in only approximated by the ideal gas law.
Redox Indicator
A redox indicator is an indicator compound that changes color at specific potential differences. A redox indicator compound must have a reduced and oxidized form with different colors and the redox process must be reversible. Further, the oxidation-reduction equilibrium needs to be reached quickly.
Redox Reactions
This is a worked example redox reaction problem showing how to calculate volume and concentration of reactants and products using a balanced redox equation.
Reduction
Reduction involves a half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons. The other half of the reaction involves oxidation, in which electrons are lost. Together, reduction and oxidation form redox reactions (reduction-oxidation = redox). Reduction may be considered the opposite process of oxidation.
Relative Density
Relative density (RD) is the ratio of the density of a substance to the density of water. It is also known as specific gravity (SG). Because it is a ratio, relative density or specific gravity is a unitless value. If its value is less than 1, then the substance is less dense than water and would float. If relative density is exactly 1, the density is the same as water. If RD is greater than 1, the density is greater than that of water and the substance would sink.
S
Salt
The word salt has different meanings in common usage and in chemistry. If you ask someone to pass the salt at dinner, this refers to table salt, which is sodium chloride or NaCl. In chemistry, sodium chloride is an example of a type of salt. A salt is an ionic compound produced by reacting an acid with a base or occurring as a natural mineral. In other words, a salt is produced by a neutralization reaction.
Salt Bridge
A salt bridge is a connection containing a weak electrolyte between the oxidation and reduction half-cells in a galvanic cell (e.g., voltaic cell, Daniell cell). Its purpose is to keep the electrochemical reaction from reaching equilibrium too quickly. If a cell is constructed without a salt bridge, one solution would quickly accumulate positive charge while the other would accumulate negative charge. This would halt the reaction and thus the generation of electricity.
Saturated
This chemistry definition refers to a saturated compound. A saturated substance is one in which the atoms are linked by single bonds. A fully saturated compound contains no double or triple bonds. Alternatively, if a molecule contains double or triple bonds, it is considered to be unsaturated.
Saturated Solution
A saturated solution is a chemical solution containing the maximum concentration of a solute dissolved in the solvent. ​The additional solute will not dissolve in a saturated solution.
Scientific Method
The scientific method is a systematic way of learning about the world around us and answering questions. The key difference between the scientific method and other ways of acquiring knowledge are forming a hypothesis and then testing it with an experiment.
Scientific Law
A law in science is a generalized rule to explain a body of observations in the form of a verbal or mathematical statement. Scientific laws (also known as natural laws) imply a cause and effect between the observed elements and must always apply under the same conditions. In order to be scientific law, a statement must describe some aspect of the universe and be based on repeated experimental evidence. Scientific laws may be stated in words, but many are expressed as mathematical equations.
Semimetals
Semimetals or metalloids are chemical elements that have properties of both metals and nonmetals. Metalloids are important semiconductors, often used in computers and other electronic devices.
Skeletal Structure
A skeletal structure is a graphical representation of the arrangement of atoms and bonds in a molecule.
Sol
A sol is a type of colloid in which solid particles are suspended in a liquid. The particles in a sol are very small. The colloidal solution displays the Tyndall effect and is stable. Sols may be prepared via condensation or dispersion. Adding a dispersing agent may increase the stability of a sol. One important use of sols is in the preparation of sol-gels.
Solid
A solid is a state of matter characterized by particles arranged such that their shape and volume are relatively stable. The constituents of a solid tend to be packed together much closer than the particles in a gas or liquid.
T
Tantalum
Tantalum is a blue-gray transition metal with element symbol Ta and atomic number 73. Because of its hardness and corrosion resistance, it is an important refractory metal and is widely used in alloys.
Technetium
transition metal with element symbol Tc and atomic number 43.
Temperature
Temperature is the property of matter which reflects the quantity of energy of motion of the component particles. It is a comparative measure of how hot or cold a material is. The coldest theoretical temperature is called absolute zero. It is the temperature where the thermal motion of particles is at its minimum (not the same as motionless). Absolute zero is 0 K on the Kelvin scale, −273.15 C on the Celsius scale, and −459.67 F on the Fahrenheit scale.
Terbium
Terbium is a soft, silvery rare earth metal with element symbol Tb and atomic number 65. It isn’t found free in nature, but it occurs in many minerals and is used in green phosphors and solid state devices. Get terbium facts and figures.
Texas Carbon
A Texas carbon is the name given to a carbon atom that forms five bonds. The name Texas carbon comes from the shape formed by five bonds radiating outwards from the carbon similar to the star in the Texas state flag. Another popular idea is that the saying “Everything is bigger in Texas” applies to carbon atoms.
Thulium
Thulium is one of the rarest of the rare earth metals. This silver-gray metals share many common properties with other lanthanides but also displays some unique characteristics.
Tin
in is silver or gray metal with atomic number 50 and element symbol Sn. It is known for its use for early canned goods and in the manufacture of bronze and pewter.
Titanium
Titanium is a strong metal used in human implants, aircraft, and many other products.
Tungsten
Tungsten is a grayish-white transition metal with atomic number 74 and element symbol W. The symbol comes from another name for the element—wolfram.
U
UN ID
A United Nations Number – also called a UN number or UN ID – is a four digit code used to identify flammable and harmful chemicals. Non-hazardous chemicals are not given UN numbers. UN numbers are assigned by the United Nations Committee of Experts on the Transport of Dangerous Goods and range from UN0001 to about UN3534. However, UN 0001, UN 0002, and UN 0003 are no longer in use.
Ultraviolet Radiation
Ultraviolet radiation is another name for ultraviolet light. It is a part of the spectrum outside the visible range, just beyond the visible violet portion.
Unit
A unit is any standard used for making comparisons in measurements. Unit conversions allow for measurements of a property that have been recorded using different units—for instance, centimeters to inches.
Universal Indicator
A universal indicator is a blend of pH indicator solutions designed to identify the pH of a solution over a wide range of values. There are several different formulas for universal indicators, but most are based on a patented formula developed by Yamada in 1933. A common mixture includes thymol blue, methyl red, bromothymol blue, and phenolphthalein.
Universal Solvent
Technically, a solvent is a component of a solution present in the greater amount. In contrast, solutes are present in a smaller amount. In the common usage, a solvent is a liquid that dissolves chemicals, such as solids, gases, and other liquids.
Unsaturated
In chemistry, the term “unsaturated” usually refers to one of two things: When referring to chemical solutions, an unsaturated solution is able to dissolve more solute. In other words, the solution is not saturated. An unsaturated solution is more dilute than a saturated solution.
Unsaturated Solution
An unsaturated solution is a chemical solution in which the solute concentration is lower than its equilibrium solubility. All of the solute dissolves in the solvent.
Uranium
Uranium is an element well-known for its radioactivity. Here are a collection of facts about the chemical and physical properties of this metal.
V
Vacuum
A vacuum is a volume that encloses little or no matter. In other words, it is a region that has a gaseous pressure much lower than that of atmospheric pressure.
Valence
Valence is typically the number of electrons needed to fill the outermost shell of an atom. Because exceptions exist, the more general definition of valence is the number of electrons with which a given atom generally bonds or number of bonds an atom forms.
Valence Bond Theory
Valence bond (VB) theory is a chemical bonding theory that explains the chemical bonding between two atoms. Like molecular orbital (MO) theory, it explains bonding using principles of quantum mechanics. According to valence bond theory, bonding is caused by the overlap of half-filled atomic orbitals. The two atoms share each other’s unpaired electron to form a filled orbital to form a hybrid orbital and bond together. Sigma and pi bonds are part of valence bond theory.
Valence Electron
A valence electron is an electron that is the most likely to be involved in a chemical reaction. They are typically the electrons with the highest value of the principal quantum number, n. Another way to think of valence electrons is that they are the outermost electrons in an atom, so they are the most susceptible to participation in chemical bond formation or ionization. The simplest way to identify the valence electrons is to look for the highest number in the electron configuration of an atom (the principal quantum number).
Valence Shell Electron Pair Repulsion Theory
Valence Shell Electron Pair Repulsion Theory (VSEPR) is a molecular model to predict the geometry of the atoms making up a molecule where the electrostatic forces between a molecule’s valence electrons are minimized around a central atom.
Vanadium
Vanadium (atomic number 23 with symbol V) is one of the transition metals. You’ve probably never encountered it in pure form, but it is found in some types of steel. Here are essential element facts about vanadium and its atomic data.
Vector 
The term “vector” has different definitions in science, primarily depending whether the topic is math/physical science or medicine/biology.
Viscosity
Viscosity is a measurement of how resistant a fluid is to attempts to move through it. A fluid with a low viscosity is said to be “thin,” while a high viscosity fluid is said to be “thick.” It is easier to move through a low-viscosity fluid (like water) than a high-viscosity fluid (like honey).
Visible light
Visible light is a range of electromagnetic radiation that can be detected by the human eye. The wavelengths associated with this range are 380 to 750 nanometers (nm) while the frequency range is approximately 430 to 750 terahertz (THz).
Volatile Substance
In chemistry, the word “volatile” refers to a substance that vaporizes readily. Volatility is a measure of how readily a substance vaporizes or transitions from a liquid phase to a gas phase. The term can also be applied to the phase change from a solid state to vapor, which is called sublimation. A volatile substance has a high vapor pressure at a given temperature compared with a nonvolatile compound.
Volumetric Flask
A volumetric flask is a type of laboratory glassware used to prepare solutions. A volumetric flask is a flat bottomed bulb with a elongated neck calibrated to hold a set volume at a mark on the neck. The flask may also be called a graduated flask or measuring flask because its mark specifies a precise volume measurement.
W
Water
Water is a chemical compound consisting of two hydrogen atoms and one oxygen atom. The name water typically refers to the liquid state of the compound. The solid phase is known as ice and the gas phase is called steam. Under certain conditions, water also forms a supercritical fluid.
Water Gas
Water gas is a combustion fuel containing carbon monoxide (CO) and hydrogen gas (H2). Water gas is made by passing steam over heated hydrocarbons. The reaction between steam and hydrocarbons produces synthesis gas. The water-gas shift reaction can be used to reduce carbon dioxide levels and enrich hydrogen content, making water gas.
Water of Crystallization
Water of crystallization is defined as water that is stoichiometrically bound into a crystal. Crystal salts containing water of crystallization are called hydrates. Water of crystallization is also known as water of hydration or crystallization water.
Water of Hydration
Water of hydration is water that is stoichiometrically bound into a crystal. While the water is found within a crystal, it is not directly bonded to a metal cation. Crystal salts containing water of hydration are called hydrates.
Wave Function
A wave function is defined to be a function describing the probability of a particle’s quantum state as a function of position, momentum, time, and/or spin. Wave functions are commonly denoted by the variable Ψ.
Wavelength
The wavelength is a property of a wave that is the distance between identical points between two successive waves. The distance between one crest (or trough) of one wave and the next is the wavelength of the wave. In equations, wavelength is indicated using the Greek letter lambda (λ).
Wave-Particle Duality
Wave-particle duality describes the properties of photons and subatomic particles to exhibit properties of both waves and particles. Wave-particle duality is an important part of quantum mechanics as it offers a way to explain why concepts of “wave” and “particle”, which work in classical mechanics, don’t cover the behavior of quantum objects. The dual nature of light gained acceptance after 1905, when Albert Einstein described light in terms of photons, which exhibited properties of particles, and then presented his famous paper on special relativity, in which light acted as a field of waves.
Weak Acid
A weak acid is an acid that partially dissociates into its ions in an aqueous solution or water. In contrast, a strong acid fully dissociates into its ions in water. The conjugate base of a weak acid is a weak base, while the conjugate acid of a weak base is a weak acid. At the same concentration, weak acids have a higher pH value than strong acids.
Weak Electrolyte
A weak electrolyte is an electrolyte that does not completely dissociate in aqueous solution. The solution will contain both ions and molecules of the electrolyte. Weak electrolytes only partially ionize in water (usually 1% to 10%), while strong electrolytes completely ionize (100%).
Weight
he everyday definition of weight is a measure of how heavy a person or object it. However, the definition is slightly different in science. Weight is the name of the force exerted on an object due to the acceleration of gravity. On Earth, weight is equal to the mass times the acceleration due to gravity (9.8 m/sec2 on Earth).
Word Equation
In chemistry, a word equation is a chemical reaction expressed in words rather than chemical formulas. A word equation should state the reactants (starting materials), products (ending materials), and direction of the reaction in a form that could be used to write a chemical equation.
Work
The word “work” means different things in different contexts. In science, it is a thermodynamic concept. The SI unit for work is the joule. Physicists and chemists, in particular, view work in relation to energy
Working Solution
Working Solution is a name given to a chemical solution made for actual use in the lab, usually made from diluting or combining stock or standard solutions.
X
Xenon
Xenon is a noble gas. The element has atomic number 54 and element symbol Xe. Like all the noble gases, xenon is not very reactive, yet it has been known to form chemical compounds. Here is a collection of xenon facts, including the element’s atomic data and properties.
X-rays
X-rays are light rays with a wavelength from 0.01 to 1.0 nanometers. Also Known As: X radiation
Y
Yield
In chemistry, yield refers to the quantity of a product obtained from a chemical reaction. Chemists refer to experimental yield, actual yield, theoretical yield, and percent yield to differentiate between calculated yield values and those actually obtained from a reaction.
Ytterbium
Ytterbium is element number 70 with an element symbol Yb. This silver-colored rare earth element is one of several elements discovered from ores from a quarry in Ytterby, Sweden. Here are interesting facts about element Yb, as well as a summary of key atomic data.
Yttrium
Yttrium oxides are a component of the phosphors used to produce the red color in television picture tubes. The oxides have potential use in ceramics and glass. Yttrium oxides have high melting points and impart shock resistance and low expansion to glass. Yttrium iron garnets are used to filter microwaves and as transmitters and transducers of acoustic energy.
Z
Zeta Potential
The zeta potential (ζ-potential) is the potential difference across phase boundaries between solids and liquids. It’s a measure of the electrical charge of particles are that are suspended in liquid. Since zeta potential is not equal to the electric surface potential in a double layer or to the Stern potential, it is often the only value that can be used to describe double-layer properties of a colloidal dispersion. Zeta potential, also known as electrokinetic potential, is measured in millivolts (mV).
Zinc
Zinc is the 24th most abundant element in the Earth’s crust.
Zinc is the fourth most common metal used today (after iron, aluminum, and copper).
Zirconium
Zirconium is a gray metal that has the distinction of being the last element symbol, alphabetically, of the periodic table. This element finds use in alloys, particularly for nuclear applications.