8.2 Lewis acids and bases (HL)

The Lewis definition of a base

A base is an electron pair donor. For a substance to act as a Lewis base, it must have a lone pair of electrons.

Coordinate (dative) covalent bonds

A coordinate (dative) covalent bond (represented by an arrrow in the direction of electron pair donation) is always formed in a Lewis acid-base reaction.

The application of the Lewis acid-base theory in organic chemistry

A nucleophile is a Lewis base, and an electrophile is a Lewis acid. The reaction between an electrophile and a nucleophile is a Lewis acid-base reaction.

Nature of science: Theories can be supported, falsified or replaced by new theories

Acid-base theories can be extended to a wider field of applications by considering lone pairs of electrons. Lewis theory does not falsify Brønsted-Lowry but extends it.

The Lewis definition of an acid

An acid is an electron pair acceptor. For a substance to act as a Lewis acid, it must have space to accept a pair of electrons in its outer shell.

Describe the Lewis acid-base theory

The Lewis definition is more general than the Brønsted-Lowry definition and can be applied to reactions that do not involve the transfer of protons. It is also useful when considering acid-base reactions in solvents other than water. The Lewis definition of acids and bases covers all the Brønsted-Lowry reactions, because the acceptance of a proton by a base must involve the donation of an electron pair to the proton.

Lewis acid-base reaction: The formation of a complex ion by a transition metal ion

The formation of a complex ion by a transition metal ion is an example of a Lewis acid-base reaction. The transition metal ion is the Lewis acid and the ligand is the Lewis base. The ligands bond to the transition metal ion through the formation of coordinate covalent bonds.