Ideas in science do notstay static. One discovery builds ~ above another. The conceptof acids and also bases hasgrown from the basic ideas that Arrhenius come Brønsted-Lowry to Lewis. Each step adds come our knowledge of the neighboring world,and makes the "big picture" also bigger.

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Lewis Acids and also Bases

Gilbert Lewis (1875-1946) proposed a third theory that acids and also bases that is even much more general than either the Arrhenius or Brønsted-Lowry theories. A Lewis acid is a substance the accepts a pair of electron to type a covalent bond. A Lewis base is a substance that donates a pair of electrons to form a covalent bond. So, a Lewis acid-base reaction is stood for by the carry of a pair of electron from a basic to an acid. A hydrogen ion, which lacks any electrons, accepts a pair the electrons. The is an acid under both the Brønsted-Lowry and Lewis definitions. Ammonia is composed of a nitrogen atom as the main atom with a lone pair the electrons. The reaction between ammonia and the hydrogen ion have the right to be portrayed as presented in the number below.

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Figure \(\PageIndex1\): Reaction between ammonia and a proton. (CC BY-NC; CK-12)

The lone pair top top the nitrogen atom is moved to the hydrogen ion, making the \(\ceNH_3\) a Lewis base while the \(\ceH^+\) is a Lewis acid.

Some reaction that perform not qualify together acid-base reactions under the other meanings do so under only the Lewis definition. An example is the reaction the ammonia v boron trifluoride.

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Figure \(\PageIndex2\): Ammonia and also boron trifluoride. (CC BY-NC; CK-12)

Boron trifluoride is the Lewis acid, when ammonia is again the Lewis base. Together there is no hydrogen ion involved in this reaction, it qualifies as an acid-base reaction just under the Lewis definition. The table below summarizes the three acid-base theories.

Table \(\PageIndex1\): Acid-Base Definitions
Type Acid Base
Arrhenius \(\ceH^+\) ions in solution \(\ceOH^-\) ions in solution
Brønsted-Lowry \(\ceH^+\) donor \(\ceH^+\) acceptor
Lewis electron-pair acceptor electron-pair donor