Question

how can we identify from valency number that the element is co-valence/ electrovalence
& Metal/Non-metal?
For example: Chlorine
Electronic Configuration: 2, 8, 7

Answer 1

Valency is the number of electron which is either loose or gain by an atom from its outermost shell...Outermost shell is also called Valence shell...and the electron present in the valence shell is called Valence electron....

Calculation of valency :

if number of electron in the outermost shell is less than 4 then its valency will be the number of electron present in the Outermost shell...For exmaple for Sodium atom , its electronic configuration is 2 , 8 , 1..

Number of electron in the outermost shell is 1 which is less than 4...so Valency will be 2 here...

If number of electron in the outermost shell is greater than 4...then valency will be 8 MINUS Number of electrons present in the outermost shell...
For example : Chlorine
Elec. Config : 2, 8 , 7
Here no of electron in outermost shell is 7 which is greater than 4...so here valency will be 8 - 7 = 1...

So valency of Chlorine is 1

Generally All metals have electrons less than 4 in their outermost shell and Non metals have electrons more than 4 in their outermost shell...