Lewis bases:
According to Lewis concept, the following species can act as Lewis bases.
1. Neutral species having at least one lone pair of electrons: For example: Ammonia, amines, alcohols. Etc act as Lewis bases because they contain a pair of electrons.
2. Negatively charged species or anions: For example:Chloride, cyanide, hydroxide ions, etc. Act as Lewis bases: CN–, Cl–, OH–
Lewis Acids:
According to Lewis concept, the following species can act as Lewis acids.
1. Molecule in which the central atom has incomplete octet: For example: In BF3, AlCl3, FeCl3, the central atom has only six electrons around it.
2. Simple cations can act as Lewis acids: All cations are expected to act as Lewis acids since they are deficient in electrons. However, cations such as Na+, K+, Ag+ ion etc has a greater electron accepting tendency and therefore, acts as Lewis acids
3. Molecules in which atoms of dissimilar electro negativities are joined by multiple bond: For example: CO2, and SO2 act as Lewis acids. Under the influence of the Lewis base, one pi electron pair will be shifted towards the oxygen atom.
4. Molecules in which the central whom has empty d-orbital’s:
Due to presence of empty d-orbital’s, the central atoms in the molecules can expand their outer octets by accepting electrons from other substance i.e. Lewis base. The molecules such as SiF4, SnCl4, PF5, act as Lewis acids:
SiF4 + 2 F– ————> [SiF6] 2-
