A lone pair is an electron pair in the outermost shell of an atom that is not shared or bonded to another atom. It is also called a non-bonding pair. One way to identify a lone pair is to draw a Lewis structure. The number of lone pair electrons added to the number of bonding electrons equals the number of valence electrons of an atom. The lone pair concept is important to valence shell electron pair repulsion (VSEPR) theory, as it helps to explain the geometry of molecules.
