Correct order of 1st ionization potential among following elements Be, B, C, N, O is
- B < Be < C < O < N
- B < Be < C < N < O
- Be < B < C < N < O
- Be < B < C < O < N
Answer
(1) B < Be < C < O < N
Solution
Ionisation enthalpy generally increases across a period, with two exceptions:
Be (2s2) > B (2s2 2p1): the 2p electron of B is shielded by the 2s electrons and is removed more easily.
N (2p3, half-filled, extra stable) > O (2p4): in O, the paired 2p electron is removed easily because of electron–electron repulsion.
As per NCERT ( kJ mol-1): B 801, Be 899, C 1086, O 1314, N 1402
B < Be < C < O < N
Answer: (1)