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960 terms · page 3 of 40
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