Question

How to know the number of valence electrons in an atom?

Answer 1

Group number can be used or we can also use electronic configuration...

Answer 2

use the group number to determine the number of valence electrons

example:

group 1

H, Li,Na ,K ,Rb,cs has 1 valence electrons

group 2

Be ,Mg,ca,sr,Ba has 2 valence electrons

group 13

B,Al, Ga,In,Ti has 3 valence electrons

group 14

c,si,Ge,sn,pb has 4 valence electrons

group 15

N, P,As,sb,,Bi has 5 valence electrons

group 16

o,s,se,Te,po has6 valence electrons

group 17

F,Cl,Br, I has7 valence electrons

group 18 (noble gas)

octet

8 valence electrons