In 1923 G. N. Lewis argued another means of looking at thereaction in between H+ and also OH- ions. In theBrnsted model, the OH- ion is the active varieties inthis reaction that accepts one H+ ion to type a covalent bond. In theLewis model, the H+ ion is the active speciesitaccepts a pair of electrons from the OH- ion to type acovalent bond.

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In the Lewis theory of acid-base reactions, bases donate pairsof electrons and also acids accept pairs of electrons. A Lewis acidis therefore any kind of substance, such as the H+ ion, thatcan accept a pair of nonbonding electrons. In other words, aLewis mountain is one electron-pair acceptor. A Lewis baseis any kind of substance, such as the OH- ion, that have the right to donatea pair of nonbonding electrons. A Lewis base is because of this an electron-pairdonor.

One advantage of the Lewis theory is the way it complementsthe version of oxidation-reduction reactions. Oxidation-reductionreactions involve a carry of electrons from one atom toanother, through a net change in the oxidation variety of one or moreatoms.


The Lewis theory suggests that mountain react with bases come sharea pair that electrons, with no change in the oxidation number ofany atoms. Many ubraintv-jp.comical reactions can be sorted into one or theother of this classes. One of two people electrons space transferred native oneatom to another, or the atoms come with each other to re-superstructure a pair ofelectrons.

The principal benefit of the Lewis theory is the means itexpands the number of acids and therefore the number of acid-basereactions. In the Lewis theory, an mountain is any kind of ion or moleculethat can accept a pair that nonbonding valence electrons. In thepreceding section, us concluded the Al3+ ion formbonds to six water molecule to offer a complicated ion.

Al3+(aq) + 6 H2O(l)

This is an instance of a Lewis acid-base reaction. The Lewisstructure that water says that this molecule has actually nonbondingpairs the valence electrons and can thus act as a Lewis base.The electron configuration of the Al3+ ion suggeststhat this ion has actually empty 3s, 3p, and also 3dorbitals that can be used to hold pairs the nonbonding electronsdonated by surrounding water molecules.

Al3+ = 3s0 3p03d0

Thus, the Al(H2O)63+ ion isformed once an Al3+ ion acting as a Lewis acid picksup 6 pairs of electron from surrounding water molecule actingas Lewis bases to give an acid-base complex, or complexion.

The Lewis acid-base theroy explains why BF3 reactswith ammonia. BF3 is a trigonal-planar moleculebecause electrons deserve to be found in only three locations in thevalence shell of the boron atom. Together a result, the boron atom is sp2hybridized, which pipeline an north 2pzorbital on the boron atom. BF3 can because of this act together anelectron-pair acceptor, or Lewis acid. It deserve to use the north 2pzorbital to pick up a pair that nonbonding electrons from a Lewisbase to kind a covalent bond. BF3 therefore reactswith Lewis bases such as NH3 to kind acid-basecomplexes in which every one of the atoms have actually a filled shell ofvalence electrons, as presented in the figure below.


The Lewis acid-base concept can also be used to define whynonmetal oxides such together CO2 dissolve in water come formacids, such together carbonic acid H2CO3.

CO2(g) + H2O(l)

In the course of this reaction, the water molecule acts together anelectron-pair donor, or Lewis base. The electron-pair acceptor isthe carbon atom in CO2. As soon as the carbon atom picks upa pair of electrons from the water molecule, the no much longer needsto form double bonds v both of the various other oxygen atoms as shownin the number below


One of the oxygen atoms in theintermediate formed when water is included to CO2 carriesa hopeful charge; one more carries a an unfavorable charge. ~ an H+ion has actually been transferred from one of these oxygen atom to theother, all of the oxygen atom in the compound room electricallyneutral. The net an outcome of the reaction in between CO2and water is therefore carbonic acid, H2CO3.

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Practice difficulty 9:

Predict even if it is the complying with ions or molecules deserve to act together either a Lewis mountain or a Lewis base.