Why is the first ionisation energy of oxygen lower than that of nitrog

1.	Why is the first ionisation energy of oxygen lower than that of nitrogen?
Answer» 1. Electronic configuration : ₇N Is² 2s² 2p_x¹ 2p_y¹ 2p_z¹ ₈O Is² Is² 2p_x² 2p_y¹ 2p_z¹ 2. Nitrogen has extra stability due to half-filled porbitals. Therefore it has higher first ionisation enthalpy. 3. Oxygen by losing one electron from 2px orbital acquires extra stability of half-filled 7-orbitals and hence has lower ionisation enthalpy. 4. Therefore oxygen has lower ionisation enthalpy than nitrogen.

Why is the first ionisation energy of oxygen lower than that of nitrogen?

Answer»

1. Electronic configuration :

₇N Is² 2s² 2p_x¹ 2p_y¹ 2p_z¹

₈O Is² Is² 2p_x² 2p_y¹ 2p_z¹

2. Nitrogen has extra stability due to half-filled porbitals. Therefore it has higher first ionisation enthalpy.

3. Oxygen by losing one electron from 2px orbital acquires extra stability of half-filled 7-orbitals and hence has lower ionisation enthalpy.

4. Therefore oxygen has lower ionisation enthalpy than nitrogen.