Question

determine the number of valence electrons in
a) Na+
b)O²-

Answer 1

Valence electrons refers to those electrons which are present in the outermost shell of the atom.

Now,

a) $\bold{Na^+}$

'+' sign represents losing of electron.

No number is written after or before +, so there is a loss of 1 electron.

Now,

Valence electrons in Na before losing = 1

After losing 1 electrons, Valence electrons = 8


b) $\bold{{O}^{2-}}$

'-' sign represents gaining of electrons.

2 is written before -, so there is a gaining of 2 electrons.

Valence electrons before gaining = 6

Valence electrons after gaining = 6 + 2 = 8