Question

Why first ionisatopn enthalpy of nitrpgen is more than that of oxygen?

Answer 1

Heya!

$first \: ionisation \: enthalpy \: of \: nitrogen \: is \: more \: than \: that \: of \: oxygen \: because$
We know that :- $electronic \: configuration \:$
of Nitrogen is...

N = 1S² 2S² 2P³

And the :-
$electronic \: configuration \:$
of Oxygen is...

O = 1S² 2S² 2P⁴

$we \: can \: see \: that \: p \: subshell \: of \: nitrogen \: is \: half \: filled.$

$we \: know \: that \: fully \: filled \: or \: half \: filled \: subshell \: are \: more \: stable \:.$

That's why Nitrogen(7) is more stable than Oxygen(8) and hence first ionisation enthalpy of Nitrogen(7) is more than Oxygen(8) !

because of the presence of half filled 'P' orbital.

Hope it helps!!