Expanded+Octets


 * Expanded Octets!**

There are three exceptions to the Octet Rule
 * 1) Molecules with an odd number of electrons
 * 2) Molecules in which an atom has less than an octet
 * 3) Molecules in which an atom has more than an octet

When a molecule has more than eight electrons in the valence shell it is known as an expanded octet. Expanded octets are more common than the other two classifications. It only occurs in molecules involving and element in the third period or above. Elements in peoriod two have 2//s// and 2//p// orbitals. These orbitals can only hold a maximum of eight electrons so expanded octets can not occur in the first two periods. Also, many of the atoms in the first two periods are too small to hold more than eight electrons around it. The larger the central atom, the more electrons it can hold around it.

An example of an expanded octet is PCl5, which has 10 electrons around the central Phosporus atom.



Another example of an expanded octet is SF6, which has 12 electrons around the central atom.