The first ionization enthalpy `(Delta_(i)H)` values of the second period elements `Li, Be` and `C` are respectively `520, 899` and `1086 kJ mol^(-1)`. Predict whther the first `Delta_(i)H` value for `B` will be more close to `690` or `990 kJ mol^(-1)`?

Answer

It will be more close to `690 kJ mol^(-1)`. The value for `b` should be lower than that of `Be` because of effective shielding of `2p`electrons from the nucleus by `2s`electrons. This is expected also because of fully filled `s-`orbital configuration of `Be`.