22.1 lattice enthalpy

lattice enthalpy definition

the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

exothermic so the value will always be negative

standard enthalpy change of formation

the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states

standard enthalpy change of atomisation definition

the enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions

always an exothermic process because bonds are broken to form gaseous atoms

first ionisation energy definition

the enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

always endothermic because energy is required to overcome the attraction between a negative electron and the positive nucleus

first electron affinity definition

the enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

first electron affinities are always exothermic because the electron being added is attracted in towards the nucleus

successive electron affinities

• when an anion has a greater charge than 1-, such as O2-, successive ionisation affinities are required.

• second electron affinities are endothermic - a second electron is being gained by a negative ion, which repels the electron away so energy must be put in to force the negatively charged electron onto the negatively charged ion