Question

How can I count valence electrons?

Answer 1

The valence electrons are the electrons that determine the most typical bonding patterns for an element.

These electrons are found in the s and p orbitals of the highest energy level for the element.

Sodium `1s^2 2s^2 2p^6 3s^1`
Sodium has 1 valence electron from the 3s orbital

Phosphorus `1s^2 2s^2 2p^6 3s^2 3p^3`
Phosphorus has 5 valence electrons 2 from the 3s and 3 from the 3p

Iron `1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6`
Iron has 2 valence electrons from the 4s

Bromine `1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^5`
Bromine has 7 valence electrons 2 from the 4s and 5 from the 4p
you can count the electrons in the out most shell

I hope this was helpful.
SMARTERTEACHER