AS definitions OCR

acid

A species that is a proton donor.

activation energy

The minimum energy required to start a reaction by the breaking of bonds.

addition polymer

A very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers).

addition polymerisation

The process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer).

addition reaction

A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule.

adsorption

The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely, a liquid.

alicyclic hydrocarbon

A hydrocarbon with carbon atoms joined together in a ring structure.

aliphatic hydrocarbon

A hydrocarbon with carbon atoms joined together in straight or branched chains.

alkali

A type of base that dissolves in water forming hydroxide ions, OH^–(aq) ions.

alkanes

The homologous series with the general formula: C_nH_2n+2.

alkyl group

An alkane with a hydrogen atom removed, e.g. CH₃, C₂H₅; alkyl groups are often shown as ‘R’.

amount of substance

The quantity whose unit of the mole. Chemists use ‘amount of substance’ as a means of counting atoms.

anhydrous

A substance that contains no water molecules.

anion

A negatively charged ion.

atom economy

atom economy = molecular mass of the desired product over sum of molecular masses of all products times one hundred.

atomic orbital

A region within an atom that can hold up to two electrons, with opposite spins.

atomic (proton) number

The number of protons in the nucleus of an atom.

average bond enthalpy

The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species.

Avogadro constant, N_A

The number of atoms per mole of the carbon-12 isotope
(6.02 × 10²³ mol^–1).

base

A species that is a proton acceptor.

biodegradable material

A substance that is broken down naturally in the environment by living organisms.

Boltzmann distribution

The distribution of energies of molecules at a particular temperature, usually shown as a graph.

bond enthalpy

The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species.

carbanion

An organic ion in which a carbon atom has a negative charge.

carbocation

An organic ion in which a carbon atom has a positive charge.

catalyst

A substance that increases the rate of a chemical reaction without being used up in the process.

cation

A positively charged ion.

cis–trans isomerism

A special type of E/Z isomerism in which there is a non-hydrogen group and a hydrogen atom on each C of a C=C double bond: the cis isomer (Z isomer) has the H atoms on each carbon on the same side; the trans isomer…