What orbitals do valence electrons occupy?

Jun 24, 2017

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 $\left[R n\right] 5 {f}^{7} 7 {s}^{2}$, i.e. empty $6 d$ 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 $5 s$ and $5 p$ orbitals of antimony, while the valence electrons occupy the $3 s$ orbitals of magnesium.

EXCEPTIONS BELOW!

d-block metals

For many $d$-block metals (such as scandium or tungsten), the $\left(n - 1\right) d$ orbitals also hold some of the valence electrons, not just the $n s$ and $n p$ orbitals.

f-block metals

For many $f$-block metals, the $\left(n - 2\right) f$ orbitals could also contain some of the valence electrons (such as for protactinium), not just the $n s$ and $n p$ orbitals.

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