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The first ionization enthalpy of carbon ...

The first ionization enthalpy of carbon is greater than that of boron, whereas the reverse is true for second ionization enthalpy. Explain.

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E.C. of C- atom is `1s^(2) 2s^(2) ` and `E.C.` of B- atom is `1s^(2) 2s^(2) 2p^(1).` The first electron to be removed in both cases is from a 2p- orbital but nuclear charge of C is more than that of b. Therefore the `Delta_(i) H_(1)` of C is greater than that of B. After the removal of first electron the second electron to be removed from C- atom is from a 2p- orbital whereas that from B- atom is form a 2s orbital . Since a s-orbital is more penetrating and hence is more strongly attracted by the nucleus than a p- orbital , therefore `Delta_(i)H_(2)` of B is higher than that of C.
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