Look at the periodic table. Do you see any relation between the number of valence electrons and group numbers?

[prasanna]

For groups 1-2 the number of valence electrons is its group number. Group 1 has one outer electron, group 2 has two, where groups 13-17 number of valence electrons is (Group number - 10). 3, 2, 1 respectively.
(i.e., 8-5 = 3; 8-6 = 2; 8-7=1)