Question

explain electron gain enthalpy in brief with the help of examples?also explain its trend in period and group .

Answer 1

Electron gain enthalpy is the energy which forms upon addition one electron to an atom in gas phase.
F + 1e → F- + ∆H = -328 kJ/mol
He + 1e → He- + ∆H = +48 kJ/mol
For groups, its value increases upon the increase in atomic number because increase in the radius of element makes weaker an interaction between a nucleus and added electron. It is known that the radius increases from the top to the down in the group.
For periods, electron gain enthalpy decreases from the first to the seventh group, which is also associated with the increase of the atomic radii. However, the enthalpy curve passes through the maxima at the second, the fifth and the eighth groups, which have the stable ns2, ns2np3 and ns2np6 electron configurations, respectively.