Question

why do fist and second ionization energies of group 14elements decrease from carbon to tin whereas the 3rd and 4th ionization energies vary irregularly?

Answer 1

the first ionization enthalpy of group 14 members is higher than the corresponding member of group 13 the influence of inner core electrons is visible here also in general the ionization enthalpy decreases down the group small decrease in ionization enthalpy from Silicon to Germanium to tin and slight increase in ionization enthalpy from tin to lead is consequence of poor shielding effect of intervening d and f orbitals and increase size of the atom