Question

Ionisation energy and electron gain enthalpy of H-atom have sign

Answer 1

Answer:

The element having very high ionization enthalpy but zero electron gain enthalpy is He. The electronic configuration of He is 1s

2

. It has completely filled s subshell.

When an electron is removed from completely filled orbital, a large amount of energy is required. Hence, He has very high ionization enthalpy. Since He has completely filled valence shell, it is little or no tendency to accept an electron. Hence, He is zero electron gain enthalpy