Question

Explain the following, give an appropriate reason.

First ionisation potential of the C-atom is greater than that of the B atom, whereas the reverse is true is for the second ionisation potential.

Answer 1

C (Z = 6) 1s² 2s² 2p_x¹ 2p_y¹. The electron removal from the p orbital is very difficult. So carbon has the highest first ionization potential. B (Z = 5) 1s² 2s² 2p¹. In boron nuclear charge is less than that of carbon, so boron has the lowest first ionization potential.

I.E₁C > I.E₁B

But it is reversed in the case of second ionization energy. Because in the case of B⁺ the electronic configuration is 1s² 2s², which is completely filled and has high ionization energy. But in C⁺ the electronic configuration is 1s² 2s² 2p¹, one electron removal is easy, so it has low ionization energy.

I.E₂B > I.E₂C