Question

Elements of group 1 and group 17 have both valency 1. Why?

Answer 1

Element of group 1 and group 17 have same valency 1.
This is because in the valance cell of group 1 element there is 1 electon is present..
and in 17 group in side the valance cell 7 electon is present..

so it is automatically get valency 1 ..

may help you

Answer 2

Valency is defined as the combining capacity of an atom. Valency is determined by the valence shell electrons.

If the valence shell has electrons less than 4, then the Valency of the compound is less than 4. If the valence shell has more than 4 electrons, valency is determined by substracting the electons from 8 i.e. 8 - n(e).

We know that group 1 and 17 have valency of 1. This is because there are only one electron in the valence of group 1 and 7 electrons present in group 17 atoms. Thus, the valency is 1.

For example,
Group 1: Hydrogen(H)- 1s¹
Here valence shell of hydrogen is 1s and there is only one electron. So the valency is 1.

Group 17: Chlorine(Cl) - 1s²2s²2p⁶3s²3p⁵

Here valence shell is 3s²3p⁵, and the electrons present here is 7. So, valency = 8-7 = 1.


Hence, the valency of both group 1 and group 17 is 1.