What orbitals do valence electrons occupy?

See here for further explanation.

For NON-transition-metal elements (i.e. non-d-block, non-f-block), we have that the valence electrons occupy the orbitals where the quantum level #n# matches the current period on the periodic table.

(NOTE: I am not simply saying "valence orbitals for all elements" because sometimes valence orbitals are not occupied at all, like in americium, with electron configuration #[Rn] 5f^7 7s^2#, i.e. empty #6d# orbitals! By the way, americium has #7# valence electrons, as its highest oxidation state so far is #+7#.)

For example, the valence electrons occupy the #5s# and #5p# orbitals of antimony, while the valence electrons occupy the #3s# orbitals of magnesium.

EXCEPTIONS BELOW!

d-block metals

For many #d#-block metals (such as scandium or tungsten), the #(n-1)d# orbitals also hold some of the valence electrons, not just the #ns# and #np# orbitals.

f-block metals

For many #f#-block metals, the #(n-2)f# orbitals could also contain some of the valence electrons (such as for protactinium), not just the #ns# and #np# orbitals.

Sometimes the #(n-1)d# orbitals ALSO hold some of the valence electrons, but sometimes they don't (such as for berkelium), depending on the particular #f#-block metal.