Boron compounds are often employed as Lewis acids due to strong electrophilic nature granted by a vacant p-orbital into which electrons can be received. It behaves as Lewis acid as its number of valence shell electrons is 3 . Thus, its octet is incomplete. e.g. B2H6 (electron deficient compounds) B(Z=5)=[He]2s22p1 ⇒ Total 5 electrons (incomplete octet)