CBSE Class 9 Answered

Valence electrons are the total number of electrons present in the valence shell or outermost shell.

Valency is the combining capapcity of an element.

Valency = no of valence electrons ( if the valence electrons are 1,2,3,4)

              = 8 - no. of valence electrons ( if the valence electrons are 5,6,7,8)

For example:

For Cl with Atomic number 17

The electronic configuration is 2,8,7

Valence electrons = 7

Valency = 8-7 = 1

For example:

For Na with atomic number 11:

The eelctronic configuration = 2,8,1

Valence electrons = 1

Valency = 1