Question

Ionization energies should depend on the effective nuclear charge that holds the electrons in the atom. Calculate Z* (Slater's Rule) for N, P, and As. Do their ionization eneregies seem to match these effective nuclear charges? If not, what other factors influence the ionization energies?

Answer 1

Electronic configuration of N - (1s²) (2s², 2p³).

Screening constant, σ = (0.35 × 4) + (0.85 × 2) = 3.10

Effective nuclear charge, Z* = Z – σ = 7 – 3.10 = 3.90

Electronic configuration of P - (1s²) (2s², 2p⁶)(3s², 3p³).

σ = (0.35 × 4) + (0.85 × 8) + (1 × 2) = 10.2

Z* = Z – σ = 14 – 10.2 = 3.8

Electronic configuration of As - (1s²)(2s²2p⁶)(3s²3p⁶)(3d¹⁰)(4s²4p³)       

σ = (0.35 × 4) + (0.85 × 18) + (1 × 10) = 26.70

Z* = Z – σ = 30 – 26.70 = 3.3

Since the effective nuclear charge decreases size of the atom increases. Due to increase in size of the atom Ionisation energy decreases. And the decrease in ionisation energy is not uniform due to poor shielding of d-electrons in case of Arsenic.