Octet Exception

[Kelly Ortega 1K]

What are the "requirements" for there to be an octect exception? What causes this or leads to this? Would it be the ionization energy?

[Chem_Mod]

The exception comes from the fact that elements in the 3 period have empty d orbitals therefore can accommodate more than 8 valence electrons.

[Ashley Curtis 2O]

So would atoms in the 3rd period fill their d orbital or go to a 4p orbital?

[Annalia_Ferrer_1F]

Also, how would they fill their d orbital? Would it steal electrons from the 3s orbital or what? I'm confused.

[Christian Hardoy 3F]

An atom can have more than 8 electrons around it, when bonding, if it has a d orbital, e.g. when n>=3. When forming bonds electrons are normally added to the valence shell of an atom until it reaches its octet. However, with elements that have d orbitals, there can be more than 8 because after it fills its "normal" valence shell, it can start to "put" electrons in the d orbital. Consider Argon, for example, which is in period 3. Its electron configuration is [Ne]3s2 3p6. However, its principal quantum number, n, is 3, meaning that it can have an angular momentum quantum number of 2, which represents a d orbital. The d orbital isn't written in the electron configuration because it isn't occupied in an Argon atom's ground state. Electrons can, however, enter the d orbital state when Argon forms bonds, which allows Argon to have more than 8 electrons in a Lewis structure.

Hope this helps!