Lewis Acid vs Base
Acids and bases are very different from each other. There are different definitions of acids and bases, but Lewis acid refers specifically to the definition of an acid that was published in 1923 by Gilbert N. Lewis. In general terms, Lewis acid is considered to be an electron pair acceptor, while Lewis base is considered electron pair donor.
Lewis acid
Lewis acid is an acidic substance that accepts a single or unique pair of electrons from some other molecule to complete its own stable group atom. For example, H + can accept a pair of electrons to complete its stable group, so it is a Lewis acid because H + requires 2 electrons.
Another way to define Lewis acid, which has been approved by IUPAC, is to recognize that Lewis acid is a molecular entity that accepts a pair of electrons and, therefore, reacts with the Lewis base to form an adduct of Lewis. The reaction that takes place between the Lewis acid and the Lewis base is that the acids accept the pair of electrons, while the Lewis base donates them. The main criterion behind the reaction is the production of an “adduct” and not a displacement reaction.
Lewis acid is classically restricted to species that have a p-empty orbital and are called flat trigonal species, for example, BR3. Here R can be halide or organic substituent.
Lewis base
The Lewis base can be defined as a species or as a basic substance that donates a pair of solitary electrons to the Lewis acids, to form a Lewis adduct. Let’s see the example of NH3 and OH-. Both are Lewis bases because they can donate a pair of electrons to Lewis acids.
NH3 gives a pair of electrons solitary to Me3B in a chemical reaction and forms Me3BNH3 which is a Lewis adduct. Me3B is a Lewis acid that accepts an electron pair of NH3.
There are some compounds that act as Lewis acids and Lewis bases. These species have the ability to accept a pair of electrons or donate a pair of electrons. When they accept a pair of electrons or a pair of solitary electrons, they act like Lewis acid. When they donate a pair of solitary electrons, they act as a Lewis base; for example, water and H2O. These compounds act as Lewis acid or Lewis base depending on the chemical reaction that takes place.
Summary:
- Lewis acid is an acidic substance that accepts a single or unique pair of electrons from another molecule to complete its own stable group of atoms (for example H +). Lewis acid is classically restricted to any species that has a p-empty orbital and is called the trigonal planar species. The Lewis base can be defined as a species or basic substance that donates a pair of solitary electrons to the Lewis acids to form a Lewis adduct.
