Question

How to find group number and period number by electron in outermost shell?

Answer 1

1) the number of shells will determine the period number .

2) number of Valence Electrons determine the group number .

NOTE : If the valence electrons are more than 2 then 10 needs to be added .

For eg. Boron has 3 valence electrons ( more than 2 ) . Therefore we add 10 .

Giving us 3 + 10 = 13 .

Similarly the group no. of Carbon , Nitrogen ..... will be 14 , 15 .....

Answer 2

period number= number of shells present in an atom

and group number = number of valence electron in the outer most shell for example

Beryllium __ Electronic configuration=2, 2

Valence electron=2

period =2

another example

Fluorine __ Electronic configuration= 2, 7

valence electron=7

period=2