Incomplete Octet
A stable bonding arrangement in which the central atom carries fewer than eight valence electrons.
Unit
Dimensionless
In depth
Common for beryllium, boron and aluminium, an incomplete octet leaves a vacant p orbital that makes these species strong Lewis acids, eager to accept a lone pair. Many relieve the deficiency by dimerising through bridging bonds.
Examples in the real world
BF₃ has six electrons on boron and readily forms F₃B←NH₃; AlCl₃ dimerises to Al₂Cl₆ with chloride bridges.