Question

If electronic configuration of an atom is 2,8,7, how can the group number of that atom be determined?

Answer 1

2 8 7, means the atomic number of the atom is 17, which is chlorine. Chlorine belongs to the halogen family and is a p block element. In the p block the electronic configuration of the atoms is ns²np^{1-6. .}In case the element belong to the p block element then the group = ( 10 + number of valence electrons present in the element)

Since it is chlorine and its electronic configuration is 3s²3p⁵. It has 7 valence electron.

Thus group = 10 +7 = 17 .Hence the element belongs to the seventeenth group.