Question

Explain why is there a phenomenal decrease in ionisation enthalpy from carbon to silicon?

Answer 1

Ionisation enthalpy of carbon (the first element of group 14) is very high (1086 kJ/mol). This is expected owing to its small size. However, on moving down the group to silicon, there is a sharp decrease in the enthalpy (786 kJ). This is because of an appreciable increase in the atomic sizes of elements on moving down the group. As silicon atom is larger in size than that of carbon, there is less attraction between the nucleus and outermost shell electrons of Si so the ionisation enthalpy required will be lesser.