Question

I.P values of post lanthanides ($Ag,Au$) have higher values down the group. Explain.

Answer 1

The ionisation energy of the elements are expected to decrease down the group with increase of distance between the valence electron and the nucleus, and well as because of the decrease in the effective nuclear charge.

The ionisation energy of gold is greater than silver due to the relativistic effect. Due to the weak shielding effect of the d and f orbitals the effective nuclear attraction on the 6s orbital electron increases greatly. This leads to a relativistic contraction of the s orbital, and consequently the 6s electron is held more tightly by the nucleus. As a result, the ionisation energy of gold is greater than that of silver.