Electron Affinity refers to an isolated atom’s attraction for an additional electron, where as electronegativity is the attraction of an atom for shared electrons when it is chemically bonded to another atom . The electron affinity is experimentally measurable while electronegativity is a relative number.
The amount of energy required to remove the most loosely bound Electron from an isolate gaseous atom is known as Ionisation Potential, also called Ionisation Energy. It may be represented as Atom (g) + I.E→ Positive Ion (g) + Electron (g) It is expressed in terms of eV/atom or kcal/mol or kJ/mol (1 eV per atom = 23.06 kcal/mol)