Question

Give reasons why in hcl the valency of the element chlorine is considered as one

Answer 1

Chlorine has 7 electrons in its outermost shell.

So, to attain stable "octet configuration", which means 8 electrons in the outermost shell; chlorine has to gain 1 electron.

After gaining 1 electron, Chloride ion is formed which is denoted by Cl⁻

Since it gains 1 electron to attain stable configuration, its Valency becomes 1

In general,

Valency = Number of valence electrons ( if valence electrons ≤ 4)

Valency = 8 - Number of valence electrons ( if Valence electrons > 4)

NOTE: (though you might know it already)

Valence electrons is the number of electrons in the outermost shell.

Hope it helps!!