Dictionary of chemistry

The Dictionary of Chemistry is a comprehensive alphabetical listing of terms and concepts related to the field of chemistry. This resource is intended for students, educators, and professionals within the scientific community.

A[edit | edit source]

Acid - A molecule or ion capable of donating a proton (hydrogen ion H+), or alternatively capable of forming a covalent bond with an electron pair (a Lewis acid).
Alkali - A base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The term is often used specifically to refer to sodium hydroxide (NaOH) or potassium hydroxide (KOH).
Alloy - A mixture of metals or a mixture of a metal and another element. Alloys are defined by metallic bonding character.
Atom - The smallest unit of a chemical element that retains its chemical properties. An atom consists of a nucleus containing protons and neutrons, with electrons orbiting this nucleus.
Avogadro's number - The number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. It is approximately 6.02214076×10²³ mol⁻¹.

B[edit | edit source]

Base (chemistry) - Chemical species that donate electrons or hydroxide ions or that accept protons.
Buffer solution - An aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it.
Bond energy - The measure of bond strength in a chemical bond. It is the heat required to break one mole of molecules into their individual atoms.

C[edit | edit source]

Catalyst - A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
Chirality (chemistry) - A geometric property of some molecules and ions; a chiral molecule/ion is non-superimposable on its mirror image.
Covalent bond - A chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs.
Crystallization - The process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal.

D[edit | edit source]

Density - A measure of mass per volume. The average density of an object equals its total mass divided by its total volume.
Diatomic molecule - Molecules composed of only two atoms, of the same or different chemical elements.
Distillation - The process of separating the components or substances from a liquid mixture by using selective boiling and condensation.

E[edit | edit source]

Electrolysis - The process that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction.
Element (chemistry) - A substance consisting of atoms which all have the same number of protons – i.e., the same atomic number.
Enthalpy - A measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.
Equilibrium constant - The value of the reaction quotient when the chemical reaction is at equilibrium. It is a quantitative measure of the strength of an equilibrium reaction.

F[edit | edit source]

Filtration - A process used to separate solids from liquids or gases using a filter medium that allows the fluid to pass through but not the solid.
Flame test - A procedure used to test qualitatively for the presence of certain metals in chemical compounds.
Flash point - The lowest temperature at which vapours of a volatile material will ignite when given an ignition source.
Fractional distillation - A technique used to separate mixtures into their individual components, based on differences in boiling points.
Free radical - An atom or group of atoms with an unpaired electron, making it highly reactive and capable of chain reactions.
Freeze-drying - A dehydration process typically used to preserve a perishable material or make the material more convenient for transport.
Functional group - A specific group of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.

G[edit | edit source]

Galvanic cell - An electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell.
Gas chromatography (GC) - An analytical method used to separate and analyze compounds that can be vaporized without decomposition.
Gibbs free energy - A thermodynamic quantity equivalent to the capacity of a system to do reversible work; it measures chemical potential.
Glass transition temperature - The temperature at which an amorphous material, such as glass or a polymer, changes from a brittle, glassy state to a ductile, rubbery state.
Gravimetric analysis - An analytical technique in which the amount of an analyte is determined by measuring the mass of a compound containing the analyte.

H[edit | edit source]

Haber process - An industrial nitrogen fixation process used to synthesize ammonia by reacting nitrogen with hydrogen.
Half-life - The time required for a quantity to reduce to half its initial value, commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay.
Haloalkane - A compound where a halogen atom has replaced one or more hydrogens on an alkane.
Heat capacity - The measurable physical quantity that specifies the amount of heat required to change a body's temperature by a given amount.
Henderson-Hasselbalch equation - An equation used to estimate the pH of a buffer solution using the pKa and the concentrations of an acid and its conjugate base.
Hess's law - A law stating that the total enthalpy change during the complete course of a chemical reaction is the same whether the reaction is made in one step or several steps.

I[edit | edit source]

Ideal gas law - The equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations.
Immunoassay - A biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution through the use of an antibody or an antigen.
Inert atmosphere - A non-reactive gas environment, typically used in chemical processes where the presence of air would affect the reaction outcome.
Infrared spectroscopy - A technique used to identify and study chemicals through their infrared spectra.
Intermolecular forces - Forces which mediate interaction between molecules, including forces of attraction or repulsion which act between molecules and other types of neighboring particles.

J[edit | edit source]

Joule - A derived unit of energy in the International System of Units. It is equal to the energy transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one meter.
Joule-Thomson effect - The temperature change of a gas or liquid when it is forced through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment.

K[edit | edit source]

Kinetic energy - The energy which a body possesses by virtue of being in motion.
Kinetic molecular theory - A theory that explains the macroscopic properties of gases and can be used to understand and explain the gas laws.
Ksp (Solubility product constant) - An equilibrium constant used to describe the saturated solution of an ionic compound.
Ketone - An organic compound characterized by a carbonyl group (C=O) linked to two carbon atoms.
Krebs cycle - A series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

L[edit | edit source]

Le Chatelier's principle - A principle that states that if a system at equilibrium is subjected to a change in concentration, temperature, volume, or pressure, then the system adjusts to counteract the imposed change and a new equilibrium is established.
Lewis acid - A chemical species that can accept an electron pair from a Lewis base to form a Lewis adduct.
Lewis base - A chemical species that donates an electron pair to form a covalent bond in a reaction.
Lewis structure - Diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.
Ligand - An ion or molecule that binds to a central metal atom to form a coordination complex.

M[edit | edit source]

Mass spectrometry - An analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio.
Melting point - The temperature at which a solid will melt to become a liquid at atmospheric pressure.
Molarity - A unit of concentration, measured in moles of solute per liter of solution.
Molecular geometry - The three-dimensional arrangement of the atoms that constitute a molecule, influencing several properties including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.
Molecular orbital - A region in a molecule where there is a high probability of finding electrons.

N[edit | edit source]

Nanotechnology - The branch of technology that deals with dimensions and tolerances of less than 100 nanometers, especially the manipulation of individual atoms and molecules.
Nernst equation - An equation that relates the reduction potential of a half-cell or full cell reaction to the standard electrode potential, temperature, and activities of the chemical species involved.
Neutralization - A chemical reaction in which an acid and a base react quantitatively with each other. In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in the solution.
Noble gases - The elements in group 18 of the periodic table, which are monatomic and have a closed outer electron shell configuration, rendering them largely inert to chemical reactions.
Nuclear magnetic resonance (NMR) - A physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation. This energy exchange results in the resonance frequency which depends on the strength of the magnetic field and the magnetic properties of the isotopes of the atoms.

O[edit | edit source]

Orbital hybridization - The concept of mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds.
Organic chemistry - The study of the structure, properties, composition, reactions, and synthesis of organic compounds that contain carbon.
Osmosis - The spontaneous movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides.
Oxidation state - A number that represents the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom.
Oxidizing agent - A substance that has the ability to oxidize other substances — in other words to cause them to lose electrons.

P[edit | edit source]

Periodic table - A tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties.
pH - A scale used to specify the acidity or basicity of an aqueous solution.
Phosphorescence - A type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs.
Photochemistry - The branch of chemistry concerned with the chemical effects of light.
Polymerization - A process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks.

Q[edit | edit source]

Quantum chemistry - The branch of chemistry whose primary focus is the application of quantum mechanics in physical models and experiments of chemical systems.
Quantum yield - A measure of the efficiency of a photochemical process or of a fluorescence process; it is defined as the number of moles of a substance produced (or reacted) per mole of photon absorbed.

R[edit | edit source]

Radical (chemistry) - Atoms, molecules, or ions with unpaired valence electrons or an open-shell configuration. They may have positive, negative, or zero charge.
Rate of reaction - The speed at which a chemical reaction proceeds.
Redox (reduction-oxidation) reactions - A type of chemical reaction that involves a transfer of electrons between two species.
Refractive index - A dimensionless number that describes how light propagates through that medium.
Resonance (chemistry) - A way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula.

S[edit | edit source]

Salt (chemistry) - An ionic compound that can be formed by the neutralization reaction of an acid and a base.
Saponification - A process that produces soap, usually from fats and lye.
Schlenk line - A commonly used chemistry apparatus developed by Wilhelm Schlenk. It consists of a dual manifold with tubing attached to a vacuum pump and inert gas supply.
Spectroscopy - The study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation.
Stereochemistry - The study of the spatial arrangements of atoms in molecules and their effects on the chemical and physical properties of substances.

T[edit | edit source]

Titration - An analytical procedure in which a reaction is run under controlled conditions to determine the concentration of a reactant.
Transition metal - Any of the metallic elements within groups 3 through 12 in the periodic table that can use the inner shell before using the outer shell to bond with other elements.
Triple bond - A chemical bond in which three pairs of electrons are shared between two atoms.
Troposphere - The lowest layer of Earth's atmosphere, where most weather occurs and where most atmospheric pollutants are found.
Tyndall effect - The scattering of light by particles in a colloid or particles in a fine suspension.

U[edit | edit source]

Ultraviolet (UV) spectroscopy - A method of spectroscopy that uses ultraviolet radiation to determine the structure and functional groups of molecules.
Uncertainty principle - In quantum mechanics, a fundamental theory that asserts a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be known simultaneously.
Unit operation - A basic step in a chemical engineering process, which is not related to the chemical reaction but is essential to the process, such as filtration, crystallization, or evaporation.
Unsaturated compound - An organic compound that contains carbon-carbon double or triple bonds and can undergo addition reactions.
Valence electron - An outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed.

V[edit | edit source]

Van der Waals forces - A general term used to define the attraction of intermolecular forces between molecules.
Vapor pressure - The pressure of a vapor in contact with its liquid or solid form.
Viscosity - A measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid.
Voltaic cell - An electrochemical cell that uses a chemical reaction to produce electrical energy.
Vulcanization - A chemical process for converting natural rubber or related polymers into more durable materials by adding sulfur or other equivalent curatives or accelerators.

W[edit | edit source]

Wavelength - The distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave.
Wet chemistry - A form of analytical chemistry that uses classical methods such as observation to analyze materials.
Work function - The minimum amount of energy required to remove an electron from a solid to a point in the vacuum immediately outside the solid surface.
X-ray crystallography - A tool used for determining the atomic and molecular structure of a crystal.

X[edit | edit source]

X-ray diffraction - A phenomenon in which the atoms of a crystal cause an incident X-ray to diffract into many specific directions.
X-ray fluorescence - An emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays.
X-ray photoelectron spectroscopy - A technique used for determining the elemental composition of materials.

Y[edit | edit source]

Yield (chemistry) - The amount of product obtained in a chemical reaction.
Young's modulus - A measure of the stiffness of an elastic material and defined by the ratio of stress to strain.

Z[edit | edit source]

Zaitsev's rule - A rule that states that in an elimination reaction, the more substituted alkene will be the more dominant product.
Zeolite - A microporous, aluminosilicate mineral commonly used as a commercial adsorbent and catalyst.
Zeta potential - A scientific term for the electrokinetic potential in colloidal dispersions.
Ziegler-Natta catalyst - A class of catalysts used in the synthesis of polymers of 1-alkenes (alpha-olefins).

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