Question

The electron gain enthalpy of beryllium and nitrogen is positive explain

Answer 1

Beryllium and nitrogen electronic configuration
Be: 1s2 2s2
N : 1s2 2s2 2p3
Be has complete 2s orbital and N has half filled 2p orbital which are much stable than partially filled orbitals.
So adding an electron will disturb the stable configuration and will increase the repulsion of electrons.
So to decrease this repulsion and increase stability Be and N instead of releasing energy provide energy to the electrons to reduce the repulsion and hence the electron gain enthalpy is positive and not negative.

Answer 2

The electron gain enthalpy of n2 and be2 is positive because be has fully filled shells (2s^2) and n2 also has half filled shells(2p^3)
Also
They belong to Group 2 and Group 15 resp.They have fully filled s orbitals and addition of new electron would move to the higher energy p . And in the 15 group they have half filled 2p orbital so they are much stable.
3. This addition of new electron is very energetically unfavorable and so this accounts for the more positive electron affinity.

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