Why are electron-gain enthalpy of Be and N positive?

Explanation

The fact that Be and N have positive electron gain enthalpy values can be explained by considering the given electron-gain processes:
`underset(("fully filled 2s-subshell"))(Be(1s^(2)2s^(2))) overset(+e)to Be^(-)(1s^(2)2s^(2)2p_(x)^(1))`
`underset(("half-filled 2p-subhsell")(N)(1s^(2)2s^(2)2p_(x)^(1)2p_(y)^(1)2p_(z)^(1)) overset(+e)to N^(-1)(1s^(2)2s^(2)2p_(x)^(2)2p_(y)^(1)2p_(z)^(1))`
It is observed that the stable electronic configuration of both Be and N atoms are disturbed by addition of an electron to each of them. consequently, such electron addition process involve absorption of energy and hence, both Be and N have positive electron-gain enthalpy values.