In the Lewis theory, an acid is any ion or molecule that can accept a pair of nonbonding valence electrons. This is an example of a Lewis acid-base reaction. The Lewis structure of water suggests that this molecule has nonbonding pairs of valence electrons and can therefore act as a Lewis base. The Lewis acid-base theroy explains why BF 3 reacts with ammonia.
BF 3 is a trigonal-planar molecule because electrons can be found in only three places in the valence shell of the boron atom. As a result, the boron atom is sp 2 hybridized, which leaves an empty 2 p z orbital on the boron atom. BF 3 can therefore act as an electron-pair acceptor, or Lewis acid. It can use the empty 2 p z orbital to pick up a pair of nonbonding electrons from a Lewis base to form a covalent bond. BF 3 therefore reacts with Lewis bases such as NH 3 to form acid-base complexes in which all of the atoms have a filled shell of valence electrons, as shown in the figure below.
Search for:. Give examples of Lewis acids and bases. The big picture gets bigger Ideas in science never stay static. Figure 1. Reaction between ammonia and proton. Figure 2. Ammonia and boron trifluoride. Summary Lewis acids and bases are defined. Examples of Lewis acids and bases are given. What is required to happen in Lewis acid-base reactions? In , G. Lewis from UC Berkeley proposed an alternate theory to describe acids and bases.
His theory gave a generalized explanation of acids and bases based on structure and bonding. Through the use of the Lewis definition of acids and bases, chemists are now able to predict a wider variety of acid-base reactions.
Lewis' theory used electrons instead of proton transfer and specifically stated that an acid is a species that accepts an electron pair while a base donates an electron pair. A coordinate covalent bond is just a type of covalent bond in which one reactant gives it electron pair to another reactant. In this case the lewis base donates its electrons to the Lewis acid.
When they do react this way the resulting product is called an addition compound, or more commonly an adduct. Lewis acids accept an electron pair. Lewis Acids are Electrophilic meaning that they are electron attracting. Lewis Bases donate an electron pair. An atom, ion, or molecule with a lone-pair of electrons can thus be a Lewis base.
Each of the following anions can "give up" their electrons to an acid, e. Complex ions are polyatomic ions, which are formed from a central metal ion that has other smaller ions joined around it. The aluminum ion is the metal and is a cation with an unfilled valence shell, and it is a Lewis Acid. Water has lone-pair electrons and is an anion, thus it is a Lewis Base.
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