Why are the first ionization energies of the higher elements of group 16 lower than those of group 15 elements?

Name elements of Group 16

Name elements of Group 18

Name first element of Group 16 to 18

What are the trends in:- ionization enthalpy of group 17 elements ?

Explain oxidation state of Group 17 elements

Explain oxidation state of Group 16 element

Explain physical state of Group 16 element

Explain physical state of Group 17 element

Elements of Group 16 generally show lower values of first ionization enthalpy compared to the elements of corresponding period of group15. why?