lone (electron) pair
Two paired electrons localized in the valence
shell on a single atom. Lone pairs should be designated with two dots. The term 'nonbonding electron pair
' is more appropriate, and is found in many modern text books.
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1137