The term “stable octet” describes the fact that many atoms in molecules are most stable when the valence shell contains effectively eight electrons. This counts both non-bonding electrons and electrons in chemical bonds between atoms. Molecules tend to be most stable when the valence shells of each atom in the molecule contain eight electrons. In the Lewis structures for F2 and CH2O (see the previous question), we see that the fluorine, carbon, and oxygen atoms are each surrounded by eight electrons. We get this total by adding both the nonbonding and bonding electrons. Since hydrogen atoms are in the first row and have just a single orbital in their valence shell, they only need two electrons (a single bond) to fulfill their analogue of a stable octet.