Arrange the following elements in increasing order of first ionization enthalpy: Li, Be, B, C, N Choose the correct answer from the options given below:
- Li < Be < B < C < N
- Li < B < Be < C < N
- Li < Be < C < B < N
- Li < Be < N < B < C
Answer
(2) Li < B < Be < C < N
Solution
Across period 2 the first ionization enthalpy generally increases.
Exception: B (2s2 2p1) < Be (2s2), because the 2p electron of B is shielded by the 2s electrons and is easier to remove than a 2s electron of Be.
Values ( kJ mol-1): Li 520, B 801, Be 899, C 1086, N 1402
Li < B < Be < C < N
Answer: (2)