Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.
What makes a solution a base? Bases are solutions that are typically described as bitter and slippery or slimy feeling. However, in an acid-base reaction, how can we tell which chemical compound is a base? Different scientists have come up with some definitions of a base, including Gilbert N. Lewis in 1923. His definition is now referred to as a Lewis base.
A Lewis base is an electron-pair donor. Because the Lewis base donates electrons, we can also say that it is a nucleophile, which is a substance that behaves as an electron donor. So, when we look at an acid-base reaction, the Lewis base donates a pair of nonbonding electrons to the acid. We can think of nonbonding electrons as loose change. We can give it away or donate it easily. In the following chemical reaction, the Lewis base (shown in red) donates its pair of nonbonding electrons to the acid. As a result, it forms a bond with the acid.
The bond formed between A and B indicates that A and B are now sharing a pair of electrons, because the single line between A and B is equivalent to two electrons.
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Let's go over some examples of compounds and ions that can act as Lewis bases, beginning with the compounds. When we look at a chemical compound, how can we recognize it as a Lewis base? Remember that Lewis bases donate electrons, which means that they have an excess of electrons or have nonbonding electrons. So, compounds that behave as Lewis bases have nonbonding electrons, as shown in the below image. Water (H2O) has two nonbonding pairs, and ammonia (NH3) has one nonbonding pair.
Phosphine, or phosphorus containing organic compounds, and amines typically act as Lewis bases because they also have nonbonding pairs. Amines are organic compounds with a lone pair of electrons, so they contain carbon (C). We can think of them as relatives of ammonia (NH3), so they also contain nitrogen (N). Phosphine is a compound with the chemical formula PH3. Phosphorus-containing organic compounds, which are compounds with phosphorus (P) and carbon (C), also act as Lewis bases.
Electrons are negatively-charged particles. If an atom, ion, or molecule has an excess number of electrons, then they can be negatively charged. So, negatively-charged ions, or anions, typically act as Lewis bases.
Let's go over a few acid-base chemical reactions so that we can learn to recognize a Lewis base.
In the following reaction, boron trifluoride (BF3) reacts with trimethylamine (N(CH3)3). Trimethylamine, which is classified as an amine, is the Lewis base because it donates its nonbonding pair of electrons to boron trifluoride.
Water (H2O) has two nonbonding pairs of electrons, so it donates one pair to the carbocation. As a result, one bond is formed and shared between carbon and oxygen. Water acts as a Lewis base because it is the electron pair donor in this reaction.
In the example below, the hydroxide ion (OH-) donates one of its nonbonding pairs to the proton (H+). The hydroxide ion acts as a Lewis base.
In 1923, Gilbert N. Lewis formulated a definition of a base, which we now refer to as a Lewis base. A Lewis base is a compound that is an electron pair donor or a nucleophile, which is a substance that donates electrons. In an acid-base reaction, we can recognize the Lewis base as the compound that donates its nonbonding electrons. Lewis bases are typically compounds that contain nonbonding pairs. Phosphine (PH3), organic compounds containing phosphorus (P); amines; and anions act as Lewis bases because nonbonding pairs are present in these compounds. These nonbonding pairs of electrons are then donated in an acid-base reaction.
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Lewis Base: Definition & Examples
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