Question

How to calculate valency of an element from its electronic configuration?

Answer 1

Hello 
______________________________________________________
The valency of an element is the electrons in last shell for example 
Electronic configuration of Na (sodium ) 

1s²2s²2p⁶3s¹

Here last electron in 3s shell which is 1 so valency  is one 
______________________________________________________

Answer 2

See the no. of electrons in valence shell.

If the no. of electrons in valence shell us between 1 to 4 then you can directlysay that its that its valency will be +{no.of valence electrons}

But if the no.of valence electrons is between 5 to 8 {Assume it to be n which is between 5 to 8}
Then its valency will be -( 8- n )