How do you determine the valence electrons?
These electrons are found in the s and p orbitals of the highest energy level for the element.
Sodium has 1 valence electron from the 3s orbital
Phosphorus has 5 valence electrons 2 from the 3s and 3 from the 3p
Iron has 2 valence electrons from the 4s
Bromine has 7 valence electrons 2 from the 4s and 5 from the 4p
you can count the electrons in the outermost shell
I hope this was helpful.