Question

Group 12 ka ionisation energy order

Answer 1

Hg > Zn > Cd

Answer 2

The general trend for ionization energy down a group is a decrease. However, for Group 12 elements (Zn, Cd, Hg), Mercury (Hg) shows an anomalous increase in ionization energy compared to Zinc (Zn) and Cadmium (Cd). This anomaly is attributed to relativistic effects, which cause contraction of the $6s$ orbital in Hg, and poor shielding by the $4f$ electrons, leading to a higher effective nuclear charge experienced by the valence electrons. Consequently, more energy is required to remove an electron from Hg. The observed order of first ionization energies is Hg (1007.1 kJ/mol) > Zn (906.4 kJ/mol) > Cd (867.8 kJ/mol).