What is an expanded octet?

An expanded octet is when an atom has more than eight valence electrons in its outermost shell. This typically occurs in atoms from the third row of the periodic table onwards, as these elements have d orbitals available for bonding.

One common example of an expanded octet is sulfur in compounds such as sulfur hexafluoride (SF6), where sulfur forms six bonds with fluorine atoms, resulting in 12 valence electrons around the sulfur atom.

Another example is phosphorus in compounds such as phosphorus pentachloride (PCl5), where phosphorus forms five bonds with chlorine atoms, resulting in 10 valence electrons around the phosphorus atom.

Expanded octets violate the octet rule, which states that atoms tend to bond in a way that allows them to have a full outer shell of eight electrons. However, in certain cases, atoms can accommodate more than eight electrons by utilizing their d orbitals for bonding.

Overall, expanded octets are seen in larger atoms with d orbitals available for bonding and are important in understanding the bonding behavior of certain elements.