How can atoms exceed the octet rule?

Question

Wyatt Adkins · Accepted Answer

Excellent query!

The n=2 shell (second row of the periodic table) requires opening up another shell, which is energetically costly, in order to accommodate any extra electrons. This is the basis for the octet rule, which is predicated on the availability of an s and three p orbitals holding eight electrons.

Any element from the third or later periods can theoretically break the octet rule because for the n=3 shell, the 3s and 3p orbitals are available to accommodate an octet. However, for n=3, the 3d orbitals are also available, albeit at a higher energy than the s and p orbitals.

For n=2 (C, N, O, F) the octet rule is iron-clad. The third and later period non-metals can break the rule. For example, the sulfate anion can be drawn as a tetrahedral of singly-bonded oxygens, but the more correct way to draw it is two double-bond oxygens and two single-bond oxygens. Similarly for sulfur hexafluoride (#SF_6#). Sulfur has clearly broken the octet rule with six bonds and twelve electrons.

Salutations!

Serenity Allen · Answer

undefined When an element is in an element beyond the second period of the periodic table, like an element from the third period, it can accommodate more than eight electrons because d orbitals are available for electron placement. This means that an element can defy the octet rule and have more than eight valence electrons in its outermost shell.