How do we know if an element can have an expanded octet?

[Henri_de_Guzman_3L]

I know it's period 3 elements and on but why? It's something to do with an available d orbital?

[Krisdylle Repollo 4H]

Yes, elements in period three and beyond have access to their d-orbitals which allow them to have more than 8 electrons on their valence shell (the d-orbital can hold 10 electrons).

[Sydney Stump]

The three scenarios that call for a violation of the octet rule are: an odd number of valence electrons, too few valence electrons, and too many valence electrons. The elements that can form the expanded octet have access to a third energy level, d-orbitals, which allows them to break the rule.

[WilliamNguyen_4L]

The elements in the third period can have more than 8 electrons because those their atoms have the d orbital its just that it is empty. When they form bonds to have an expanded octet the surplus electrons fill the D orbital.