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

The electronic configuration of carbon and boron are as follows:

C: 1S²,2s², 2px¹,2py¹

B: 2S², 2s²,  2px¹

Due to higher nuclear charge in carbon, the force of attraction towards valency electron is more in carbon atom and hence the first ionization energy is greater than boron atom. After loss of one electron, the mono-valent cations have the configurations as follows:

C: 1S2 ,2s2 2px1,

B: 2S² , 2s²,  

Configuration of B+ is stable one and hence the removal of electron is difficult in comparison to C+. Hence, second ionization potential of boron is higher than carbon.

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