What Is the Duet Rule in Chemistry?

The duet rule in chemistry is an adaptation of the octet rule that applies to hydrogen and lithium. Because atoms of these elements only possess s orbitals, two electrons can create a filled energy state like the nearest noble gas, helium.

According to the octet rule, atoms are most stable when they form bonds and acquire a full shell of electrons in a configuration like that of the nearest noble gas. For most atoms, a set of eight electrons is the goal. However, just as hydrogen and lithium are exceptions with fewer electrons, others can have more, such as bromine and phosphorus with 10 electrons.