Definitions (Learn)

Atoms of the same element with different numbers of neutrons and different masses

The weighted mean mass of an atom of an element compared with one–twelfth of an atom of carbon–12

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous +1 ions

A group of atomic orbitals with the same principal quantum number, n, also known as a main energy level.

A group of orbitals of the same type within a shell.

A region around the nucleus which can hold up to 2 electrons, with opposite spins.

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

A strong dipole-dipole attraction between an electron deficient hydrogen atom of -NH, -OH or HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule.

A species that releases H+ ions in aqueous solution

An acid that dissociates completely in solution

An acid that dissociates only partially in solution

A compound that neutralises an acid to form a salt

A type of base that dissolves in water forming hydroxide ions, OH- (Aq) ions

The product of a reaction in which the H+ ions from the acid are replaced by either ammonium or metal ions

A loss of electrons or an increase in oxidation number

Gain of electrons or a decrease in the oxidation number.

A reaction involving both oxidation and reduction

A series of organic compounds with the same functional group but with each successive member differing by CH2

An atom or a group of atoms which is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.

Compounds with the same structural formula but a different arrangement of atoms in space

A type of stereoisomerism in which different groups attached to each carbon of a C=C of a double bond may be arranged differently in space because of the restricted rotation of the C=C bond.

A special type of E/Z isomerism in which there are two non-hydrogen groups and two hydrogen atoms around the C=C double bond: the cis isomer (Z isomer) has H atoms on each carbon atom on the same side; the trans isomer (E isomer) has H atoms on each carbon on different sides.

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard condition, all reactants and products being in their standard states.

the enthalpy change that takes place when one mole of a compound in its standard state is formed from its constituent elements in their standard states under standard conditions.