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Lewis Theory
The Lewis definition is the most general theory, having no requirements for solubility or protons.
Lewis Acids and Bases


  1. An acid is a substance that accepts a lone pair of electrons.

  2. A base is a substance that donates a lone pair electrons.

Lewis acids and bases react to create an adduct, a compound in which the acid and base have bonded by sharing the electron pair. Lewis acid/base reactions are different from redox reactions because there is no change in oxidation state.

This reaction shows a Lewis base (NH3) donating an electron pair to a Lewis acid (H+) to form an adduct (NH4+).


Amphoterism and Water[edit]

Substances capable of acting as either an acid or a base are amphoteric. Water is the most important amphoteric substance. It can ionize into hydroxide (OH-, a base) or hydronium (H3O+, an acid). By doing so, water is


480


  1. Increasing the H+ or OH- concentration (Arrhenius),

  2. Donating or accepting a proton (Brønsted-Lowry), and

  3. Accepting or donating an electron pair (Lewis).

Important A bare proton (H+ ion) cannot exist in water. It will form a hydrogen bond to the nearest water molecule, creating thehydronium ion (H3O+). Although many equations and definitions may refer to the "concentration of H+ ions", that is a misleading abbreviation. Technically, there are no H+ ions, only hydronium (H3O+) ions. Fortunately, the number of hydronium ions formed is exactly equal to the number of hydrogen ions, so the two can be used interchangeably.

H+ ions actually exist as hydronium, H3O+.
Water will dissociate very slightly (which further explains its amphoteric properties).

The presence of hydrogen ions


indicates an acid, whereas the presence

of hydroxide ions indicates a base.

Being neutral, water dissociates into

both equally.


This equation is more accurate—

hydrogen ions do not exist in water

because they bond to form hydronium.



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