First ionisation energy of copper is higher than those of alkali metals, while second and third ionisation energies are lower. Explain.

Explanation

Copper has small size compared to alkali metals in their period. Its elecronic configuration is `[Ar]3d^(10)4s^1` As filled 3d-subshell is less effective in shielding the outer 8-electrons than s- and p-subshell and therefore, s-electron in copper is more tightly held by the nucleus than in alkali metals. Hence, its first ionisation energy is higher than for alkali metals. However, second and third ionisation energy values of copper are lower as compared to those of alkali metals due to removal of electrons from diffused d-orbitals.