Octet rule question

[longjump]

Which atoms MUST form an octet? Do these atoms always form one or does it depend on the molecule?

[Rian Montagh 2K]

Most atoms form an octet, H, He, and Be can have 2 valence, and elements in the 3rd period and up can have expanded octets into the d orbitals. B and Al sometimes only have 6 valence. Also, I believe that free radicals can mess up the octet rule. I am guessing that there are no atoms that MUST have an octet, and that it depends on the specific molecule or ion.

[shaunajava2e]

elements in the 3rd period and onwards are able to take advantage of their empty d orbital and expand their octet past the 8 electrons that come with the p and s orbitals.

[Phoebe Chen 4I]

All the elements with orbitals 3p and up have an expanded octet. Everything before that must adhere to the octet rule. However, elements with only 1s orbitals, and elements with only up to 2s orbitals do not adhere to octet rule and instead only need to have 2 valence or bonded electrons.

[Sang Hyoun Hong 3G]

Every element before period 3 should follow the octet rule. Elements in period 3 have access to the d orbital so can have an expanded octet.

[Rebecca Park]

Every element after period 2 can follow the octet rule.

[Yixiao Hu 3C]

atoms before the period 3 must have a octet rule. Meanwhile, except the central atom, atoms aside should also obey the octet rule