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

(N/A) The ionisation enthalpy of carbon (the first element of group $14$) is very high $(1086 \ kJ/mol)$. This is expected due to its small atomic size.
However,on moving down the group to silicon,there is a sharp decrease in the ionisation enthalpy $(786 \ kJ/mol)$.
This significant decrease is primarily due to the appreciable increase in the atomic size of elements as we move down the group,which reduces the effective nuclear attraction on the valence electrons.