A lone pair (nonbonding pair) is a pair of valence electrons that belongs to a single atom and is not shared in a bond; it is drawn as a pair of dots in a Lewis structure. Although it forms no bond, a lone pair occupies space around the central atom and so influences molecular geometry. In water, for example, the two lone pairs on oxygen push the O–H bonds closer together.

孤对(非键电子对)是属于单个原子、未在键中共享的一对价电子;在路易斯结构中画作一对点。孤对虽不形成键,却占据中心原子周围的空间,因而影响分子几何构型。例如在水中,氧上的两对孤对把 O–H 键挤得更近。