Editing Acid–base reaction (section)

===Lewis definition===
{{Further|Lewis acids and bases}}
The hydrogen requirement of Arrhenius and Brønsted–Lowry was removed by the Lewis definition of acid–base reactions, devised by [[Gilbert N. Lewis]] in 1923,<ref name="lewis_1">{{harvnb|Miessler|Tarr|1991|p=166}} – Table of discoveries attributes the date of publication/release for the Lewis theory as 1924.</ref> in the same year as Brønsted–Lowry, but it was not elaborated by him until 1938.<ref name=review1940/> Instead of defining acid–base reactions in terms of protons or other bonded substances, the Lewis definition defines a base (referred to as a ''Lewis base'') to be a compound that can donate an ''[[electron pair]]'', and an acid (a ''Lewis acid'') to be a compound that can receive this electron pair.<ref name="lewis_2">{{harvnb|Miessler|Tarr|1991|pp=170–172}}</ref>

For example, [[boron trifluoride]], {{chem2|BF3}} is a typical Lewis acid. It can accept a pair of electrons as it has a vacancy in its [[octet rule|octet]]. The [[fluoride]] ion has a full octet and can donate a pair of electrons. Thus
<math chem display=block>\ce{BF3 + F- -> BF4-}</math>
is a typical Lewis acid, Lewis base reaction. All compounds of [[boron group|group 13]] elements with a formula {{chem2|AX3}} can behave as Lewis acids. Similarly, compounds of [[group 15]] elements with a formula {{chem2|DY3}}, such as [[amine]]s, {{chem2|NR3}}, and [[organophosphine|phosphine]]s, {{chem2|PR3}}, can behave as Lewis bases. [[Adduct]]s between them have the formula {{chem2|X3A←DY3}} with a [[dative covalent bond]], shown symbolically as ←, between the atoms A (acceptor) and D (donor). Compounds of [[group 16]] with a formula {{chem2|DX2}} may also act as Lewis bases; in this way, a compound like an [[ether]], {{chem2|R2O}}, or a [[thioether]], {{chem2|R2S}}, can act as a Lewis base. The Lewis definition is not limited to these examples. For instance, [[carbon monoxide]] acts as a Lewis base when it forms an adduct with boron trifluoride, of formula {{chem2|F3B←CO}}.

Adducts involving metal ions are referred to as co-ordination compounds; each ligand donates a pair of electrons to the metal ion.<ref name="lewis_2"/> The reaction
<math chem display=block>\ce{[Ag(H2O)4]+ + 2 NH3 -> [Ag(NH3)2]+ + 4 H2O}</math>
can be seen as an acid–base reaction in which a stronger base (ammonia) replaces a weaker one (water).

The Lewis and Brønsted–Lowry definitions are consistent with each other since the reaction
<math chem display=block>\ce{H+ + OH- <=> H2O}</math>
is an acid–base reaction in both theories.