The factors affecting electron gain enthalpy and the trend in its variation in the periodic table are:
- Atomic size – As the distance between the nucleus and the outermost shell rises, the tendency of the atom to gain electron diminishes, and the electron gain enthalpy become less negative.
- Effective nuclear charge – The effective nuclear charge grows as we move from left to right in a period and drops as we move down the group, resulting in the attraction of electrons from the outermost shell.
- Electronic configuration – The ability of an element to gain electrons is determined by its stability. Elements with fully or partially filled stable orbitals have a low tendency to gain electrons, and so have a low electron gain enthalpy. The electron gain enthalpy grows more negative across periods. The electron gain enthalpy decreases as one moves down the group.