Classify the following species into Lewis acids and bases and show how these act as such:
(i) `BCl_3` (ii) `H^(+)` (iii) `F^(-)` (iv) `HO^(-)`

Explanation

Strategy: A Lewis acid is any species that can accept a share in an electron pair while a Lewis base in any species that can make available or donate a share in an electron pair.
Solution:
(i) `BCl_3` acts as a Lewis acid because the central B atom has incomplete octet and, therefore, can accept a lone pair of electrons from species like ammonia or amine molecules.
(ii) A proton is a Lewis acid as it can form an H atom by accepting a lone pair of electrons from species like hydroxide ion and fluoride ion.
(iii) Fluoride ion acts as a Lewis base as it can donate any one of its four lone pairs of electrons.
(iv) Hydroxide ion is a Lewis base as it can donate any one of its three lone pairs of electrons.