Lewis Acids
1. Lewis acids are substances that can accept one or more lone pair of electrons.
2. All metal ions (or) atoms can act as Lewis acids. Examples: Fe2+ , Fe3+ , Cu2+ , Cr3+
3. Molecules that contain a polar double bond can act as Lewis acids. Examples: SO2 , CO2 , SO3
4. Molecules in which the central atom can expand its act due to the availability of empty d-orbitais can act as Lewis acid. Example: SiF4 , SF4 , FeCI3
5. Carbonium ion (CH3)3C+ can act as Lewis acid
6. Electron deficient molecules such as BF3 , AlCl3 , BeF2 act as Lewis acid (electron pair acceptors).
Lewis Bases
1. Lewis bases are substances that can donate one or more lone pair of electrons.
2. All anions can act as Lewis bases. Examples: F- , Cl- , CN- , SO42-
3. Molecules that contain carbon-carbon multiple bond. Example: CH2 = CH2 , CH = CH
4. All metal oxides can act as Lewis bases. Examples : CaO, MgO, Na2O
5. CH2- carbanion cari act as Lewis acid
6. Electron rich molecules such as NH3 , H2O, ROH, R – O – R, R – NH2 act as Lewis base (Electron pair donors)