Question

Explain why? 

(a) Ionization enthalpy of nitrogen is more than that of oxygen. 

(b) Electron gain enthalpy of fluorine is less than that of chlorine. 

(c) Anionic radius is more than the cationic radii.

Answer 1

(a) ₇N = 1s², 2s², 2px¹,2py¹,2pz¹

₈O = 1s², 2s², 2px²,2py¹,2pz¹

Since nitrogen has half-filled p-orbital which are more stable than incompletely filled p-orbitals of oxygen. So, ionization enthalpy of nitrogen is more than that of oxygen.

(b) ₉F = 1s², 2s², 2px²,2py²,2pz¹

₁₇Cl = 1s², 2s², 2p⁶,3s²,3px², 3py²,3pz¹

Fluorine has two shells and the incoming electron is to be accommodated in the second shell. As the radius of second shell is smaller than that of third shell so incoming electron has to face electronic repulsion due to increased electron density. So, electron gain enthalpy of fluorine is less than that of chlorine.

(c) Anion in formed by gain of electron by adding extra electron, the net nuclear charge decreases on the valence shell. Hence the radius of anion is greater than that of parent atom. On the other hand the cations are formed by loss of electron, this removes the valence shell and as the number of shells decreases, the radius of cation also decrease as compared to parent atom.