# Ionisation energies of Carbon and Boron

The first ionisation energy of Carbon atom is greater than that of Boron atom whereas, the reverse is true for the second ionisation energy.

In order to explain the above statement I considered the electronic configurations of Carbon and Boron atoms: $$C \to 1s^2 2s^2 2p^2$$ $$B \to 1s^2 2s^2 2p^1$$ Carbon atom is smaller in size than Boron atoms, this means increased effective nuclear charge in Carbon but this also means more inter-electronic repulsions, the contributions of these two effects on the ionisation energy is opposite, How do I determine which effect dominates? Moreover there is more shielding in Carbon due to extra p electron as compared to Boron but the stability of the product obtained on removal of an electron is more in Boron(closed shell configuration is attained), is it possible to compare their first ionisation energies logically? I don't have problem with second ionisation energies as it is more difficult to remove and electron from closed $$2s^2$$ shell than $$2p^1$$.