Why does an electron give away energy when its accepting an electron? Why does it have to give away energy? In what form is this energy released?

Also why is:

Ionization Energy in terms of positive KJ/mol

and Electron Affinity in negative KJ/mol.

IT IS THE FUNDA OF KINETIC ENERGY IN GROUND STATE LEVEL,in ground state level the collission occours with maximum energy,so one which gives electron or energy to other transfers the KE to other or transfer the momentum.

IE is always valid for per mole,KJ/or K cal can be varried.
Electron affinityis defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when anelectronis added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining anelectron.