Explain Lewis acid base theory with suitable example. Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base.
a. `OH^(-)` b. `F^(-)` c. `H^(+)` d. `BCl_(3)`

Explanation

Lewis acid: The substance which can accept an electron paor to form a coordinate covalent bond is called Lewis acid.
Types of Lewis acids:
1. all +vely charged metal ions or cations act as Lewis acids.
Ex: `Ag^(+),CO^(+3),Cu^(+2),Fe^(+3)`, etc.
2. Electron deficient compounds whose central atom has an incomplete octet, possessing an empty orbital acts as Lewis acid.
eg: `BF_(3),BCl_(3),AlCl_(3),FeCl_(3)`.
3. Compounds in which central atom has vacant 'd' orbitals and which can expand its octet.
eg: `SiF_(4),SnCl_(4),SF_(4),TeF_(4), FeCl_(3)`
4. Molecules having multiple bonds between atoms of different electronegativities
eg: `CO_(2),SO_(2),SO_(3),NO_(2),Cl_(2)O_(7),P_(4)O_(10)`.
5. Elements with an electron sextet.
eg: S,O
Lewis base: The substance which donates electron pair to form a coordinate covalent bond is called Lewis base.
Types of Lewis bases:
1. all anions will act as Lewis bases.
eg: `Cl^(-),OH^(-),CN^(-),NH_(2)^(-),F^(-),SCN^(-)`
2. Molecules with one or two Ione pairs on the central atom.
eg: `H_(2)O,NH_(3),R-OH,R-NH_(2),R-O-R,C_(5)H_(5)N`.
3. Molecules with multiple bonds.
eg: `CO,NO,HC-=CH,H_(2)C=CH_(2)`
a. `OH^(-)` is Lewis base b. `F^(-)` is Lewis base,
c. `H^(+)` is Lewis acid d. `BCl_(3)` is Lewis acid.