Octet rule

The octet rule is one of the most poorly defined rules of chemistry. The octet rule states that atoms tend to ionise in such a way that they have eight electrons in their valance shells, similar to the electronic configuration of a noble gas. (In simple terms, atoms are more stable when their outer shells are empty, full, or have a multiple of 8 electrons in the outer shell. See electron shells.)

This ionisation occurs primarily in two ways, electrovalent bonding and covalent bonding.

However, the octet rule seems to be more violated than it is followed. Some of the atoms that follow the octet rule are:

• carbon, C
• oxygen, O
• the halogens

However, the exceptions are plenty:

• hydrogen only needs one electron to have a noble gas structure (that of helium), and lithium needs to lose one.
• any molecule with an odd number of electrons
• any atom that forms more than four bonds disobeys the octet rule most frequently
• atoms in periods greater than 2 violate the octet rule because their electron shells can hold more than eight electrons