Chemistry terms starting with A

Anodising Electrochemistry & Redox μm An electrolytic process that thickens the natural protective oxide layer on a metal, especially aluminium. 2Al + 3H₂O → Al₂O₃ + 6H⁺ + 6e⁻

Anti-Markovnikov Addition Organic Chemistry Dimensionless Addition in which the hydrogen attaches to the carbon bearing fewer hydrogens, reversing the normal regiochemistry.

Antibonding Molecular Orbital Chemical Bonding & Molecular Structure Dimensionless A molecular orbital higher in energy than its parent atomic orbitals, whose occupation destabilises the molecule. ψ* = ψ_A − ψ_B

Approach to Equilibrium Chemical Equilibrium s The time-dependent process by which a reacting system moves towards its equilibrium composition.

Aqueous Solution Solutions & Colligative Properties mol/L A solution in which water is the solvent, denoted by the state symbol (aq).

Arene Organic Chemistry Dimensionless An aromatic hydrocarbon containing one or more benzene rings. CₙH₂ₙ₋₆

Aromaticity Organic Chemistry kJ/mol The special stability of planar cyclic molecules with a continuous, fully conjugated system of delocalised pi electrons. planar, cyclic, conjugated, 4n+2 π

Arrhenius Equation Chemical Kinetics & Catalysis Various The equation describing how a rate constant varies with temperature and activation energy. k = A e^(−Ea/RT)

Arrhenius Theory Acids, Bases & Salts Dimensionless The theory defining an acid as a substance that produces H⁺ ions in water and a base as one that produces OH⁻ ions. HA → H⁺ + A⁻; BOH → B⁺ + OH⁻

Artificial Radioactivity Nuclear & Radiochemistry Bq Radioactivity in nuclides created by bombarding stable nuclei with particles rather than found in nature.

Association Solutions & Colligative Properties Dimensionless The joining of solute molecules in solution into larger aggregates, reducing the effective number of particles. nA → Aₙ

Association Constant Chemical Equilibrium L/mol The equilibrium constant for the combination of two species into a single associated entity, the reciprocal of the dissociation constant. Ka = 1 / Kd

Atom Foundations of Chemistry Dimensionless The smallest particle of an element that retains the chemical identity of that element.

Atomic Absorption Spectroscopy Analytical Chemistry & Spectroscopy ppm A technique that measures the concentration of a metal from the light its free gaseous atoms absorb. A = εlc

Atomic Emission Spectroscopy Analytical Chemistry & Spectroscopy ppm A technique that identifies and quantifies elements from the light their excited atoms emit.

Atomic Emission Spectrum Atomic Structure & Periodicity nm The pattern of discrete wavelengths emitted when excited atoms of an element return to lower energy states. ΔE = hν

Atomic Mass Unit Foundations of Chemistry u (Da) A mass unit defined as exactly one twelfth the mass of a free, unbound carbon-12 atom in its ground state. 1 u = 1.66053907 × 10⁻²⁷ kg

Atomic Number Atomic Structure & Periodicity Dimensionless The number of protons in the nucleus of an atom, which uniquely identifies the element. Z = number of protons

Atomic Orbital Atomic Structure & Periodicity Dimensionless A mathematical function describing the region around a nucleus where an electron of given energy is most likely to be found. |ψ|² = probability density

Atomic Radius Atomic Structure & Periodicity pm A measure of the size of an atom, usually taken as half the distance between the nuclei of two bonded identical atoms. r = d(X–X) / 2

Atomicity Foundations of Chemistry Dimensionless The number of atoms present in one molecule of an element.

Aufbau Principle Atomic Structure & Periodicity Dimensionless The rule that electrons occupy the lowest-energy orbital available before filling higher-energy ones. fill in order of increasing (n + l)

Autocatalysis Chemical Kinetics & Catalysis Dimensionless Catalysis of a reaction by one of its own products.

Average Kinetic Energy States of Matter & Gas Laws J The mean translational kinetic energy of the particles in a sample, dependent only on absolute temperature. KE = (3/2)kT per molecule

Terms starting with A