AQA A LEVEL CHEMISTRY DEFINITIONS
Relative Atomic Mass - ANSWER-The weighted mean mass of an atom of an element
relative to 1/12 of the mass of one atom of carbon-12
First Ionisation energy - ANSWER-The energy required to remove an electron from
each atom in one mole of gaseous atoms
Acid - ANSWER-A species that is a proton donor
Activation Energy - ANSWER-The minimum energy required to start a reaction by the
breaking of bonds
Addition Polymer - ANSWER-The process in which unsaturated alkene molecules ass
on to a growing polymer chain one at a time to form a very long saturated molecule
chain
Addition Reaction - ANSWER-A reaction in which a reactant is added to an unsaturated
molecule to make a saturated molecule
Adsorption - ANSWER-The process that occurs when a gas, liquid or solid is held to the
surface of a solid, or, more rarely, a liquid
Alicyclic Hydrocarbon - ANSWER-A hydrocarbon with carbon atoms joined together in a
ring structure
Aliphatic Hydrocarbon - ANSWER-A hydrocarbon with carbon atoms joined together in
straight or branched chains
Alkali - ANSWER-A type of base that dissolves in water forming hydroxide ions
Alkanes - ANSWER-The homologous series with the general formula CnH2n+2
Alkyl Group - ANSWER-An alkane with a hydrogen ion removed. Alkyl groups are often
shown as 'R'
Amount of Substance - ANSWER-The quantity whose unit is the mole
Anhydrous - ANSWER-A substance containing no water molecules
Anion - ANSWER-A negatively charged ion
Atom Economy - ANSWER-(molecular mass of the desired product/sum of molecular
masses of all products) x100
, Atomic Orbital - ANSWER-A region within an atom that can hold up to two electrons,
with opposite spins
Atomic Number - ANSWER-The number of protons in the nucleus of an atom
Average Bond Enthalpy - ANSWER-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 substance
Avogadro Constant - ANSWER-The number of atoms per mole of the carbon-12
isotope. (6.02 x 10^23)
Base - ANSWER-A species that is a proton acceptor
Biodegradable Material - ANSWER-A substance that is broken down naturally in the
environment of a living organism
Boltzmann Distribution - ANSWER-The distribution of energies of molecules at a
particular temperature, usually shown as a graph.
Bond Enthalpy - ANSWER-The enthalpy change hat takes place when breaking by
homolytic fission 1 mol of a given bond in the molecules of a gaseous species
Carbanion - ANSWER-An organic ion in which a carbon atom has a negative charge
Carbocation - ANSWER-An organic ion in which a carbon ion has a positive charge.
Catalyst - ANSWER-A substance that increases the rate of a chemical reaction without
it being used up
Cation - ANSWER-A positively charged ion
Cis-Trans Isomerism - ANSWER-A special type of E/Z isomerism in which there is a
non-hydrogen group and a hydrogen on each C of a C=C double bond: the cis isomer
has the H atom of each carbon on the same side, the trans isomer has the H atom of
each carbon on different sides
Compound - ANSWER-A substance formed from two or more chemically bonded
elements in a fixed ratio, usually shown by a chemical formula.
Concentration - ANSWER-The amount of solute, in mol, per 1 dm^2
Coordinate Bond - ANSWER-A shared pair of electrons which has been provided by
one of the bonding atoms only; also called a dative covalent bond.
Relative Atomic Mass - ANSWER-The weighted mean mass of an atom of an element
relative to 1/12 of the mass of one atom of carbon-12
First Ionisation energy - ANSWER-The energy required to remove an electron from
each atom in one mole of gaseous atoms
Acid - ANSWER-A species that is a proton donor
Activation Energy - ANSWER-The minimum energy required to start a reaction by the
breaking of bonds
Addition Polymer - ANSWER-The process in which unsaturated alkene molecules ass
on to a growing polymer chain one at a time to form a very long saturated molecule
chain
Addition Reaction - ANSWER-A reaction in which a reactant is added to an unsaturated
molecule to make a saturated molecule
Adsorption - ANSWER-The process that occurs when a gas, liquid or solid is held to the
surface of a solid, or, more rarely, a liquid
Alicyclic Hydrocarbon - ANSWER-A hydrocarbon with carbon atoms joined together in a
ring structure
Aliphatic Hydrocarbon - ANSWER-A hydrocarbon with carbon atoms joined together in
straight or branched chains
Alkali - ANSWER-A type of base that dissolves in water forming hydroxide ions
Alkanes - ANSWER-The homologous series with the general formula CnH2n+2
Alkyl Group - ANSWER-An alkane with a hydrogen ion removed. Alkyl groups are often
shown as 'R'
Amount of Substance - ANSWER-The quantity whose unit is the mole
Anhydrous - ANSWER-A substance containing no water molecules
Anion - ANSWER-A negatively charged ion
Atom Economy - ANSWER-(molecular mass of the desired product/sum of molecular
masses of all products) x100
, Atomic Orbital - ANSWER-A region within an atom that can hold up to two electrons,
with opposite spins
Atomic Number - ANSWER-The number of protons in the nucleus of an atom
Average Bond Enthalpy - ANSWER-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 substance
Avogadro Constant - ANSWER-The number of atoms per mole of the carbon-12
isotope. (6.02 x 10^23)
Base - ANSWER-A species that is a proton acceptor
Biodegradable Material - ANSWER-A substance that is broken down naturally in the
environment of a living organism
Boltzmann Distribution - ANSWER-The distribution of energies of molecules at a
particular temperature, usually shown as a graph.
Bond Enthalpy - ANSWER-The enthalpy change hat takes place when breaking by
homolytic fission 1 mol of a given bond in the molecules of a gaseous species
Carbanion - ANSWER-An organic ion in which a carbon atom has a negative charge
Carbocation - ANSWER-An organic ion in which a carbon ion has a positive charge.
Catalyst - ANSWER-A substance that increases the rate of a chemical reaction without
it being used up
Cation - ANSWER-A positively charged ion
Cis-Trans Isomerism - ANSWER-A special type of E/Z isomerism in which there is a
non-hydrogen group and a hydrogen on each C of a C=C double bond: the cis isomer
has the H atom of each carbon on the same side, the trans isomer has the H atom of
each carbon on different sides
Compound - ANSWER-A substance formed from two or more chemically bonded
elements in a fixed ratio, usually shown by a chemical formula.
Concentration - ANSWER-The amount of solute, in mol, per 1 dm^2
Coordinate Bond - ANSWER-A shared pair of electrons which has been provided by
one of the bonding atoms only; also called a dative covalent bond.
