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

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In the Lewis concept of acid-base reactions, bases donate pairsof electrons and acids expropriate pairs of electrons. A Lewis acidis therefore any type of substance, such together the H+ ion, thatcan expropriate a pair that nonbonding electrons. In other words, aLewis mountain is one electron-pair acceptor. A Lewis baseis any substance, such as the OH- ion, that deserve to donatea pair the nonbonding electrons. A Lewis base is as such an electron-pairdonor.

One benefit of the Lewis theory is the method it complementsthe version of oxidation-reduction reactions. Oxidation-reductionreactions show off a deliver of electrons from one atom toanother, through a net change in the oxidation variety of one or moreatoms.


The Lewis theory argues that acids react with bases come sharea pair the electrons, with no readjust in the oxidation numbers ofany atoms. Many cg-tower.comical reactions deserve to be sorted right into one or theother of this classes. Either electrons are transferred native oneatom to another, or the atoms come together to re-publishing a pair ofelectrons.

The principal advantage of the Lewis concept is the method itexpands the number of acids and also therefore the number of acid-basereactions. In the Lewis theory, an acid is any type of ion or moleculethat deserve to accept a pair that nonbonding valence electrons. In thepreceding section, we concluded the Al3+ ion formbonds to 6 water molecules to provide a facility ion.

Al3+(aq) + 6 H2O(l)

This is an instance of a Lewis acid-base reaction. The Lewisstructure the water says that this molecule has nonbondingpairs that valence electrons and also can as such act together a Lewis base.The electron construction of the Al3+ ion suggeststhat this ion has empty 3s, 3p, and also 3dorbitals that have the right to be provided to host pairs the nonbonding electronsdonated by neighboring water molecules.

Al3+ = 3s0 3p03d0

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

The Lewis acid-base theroy describes why BF3 reactswith ammonia. BF3 is a trigonal-planar moleculebecause electrons deserve to be discovered in just three places in thevalence shell of the boron atom. As a result, the boron atom is sp2hybridized, which leaves an empty 2pzorbital on the boron atom. BF3 can as such act as anelectron-pair acceptor, or Lewis acid. It deserve to use the empty 2pzorbital to pick up a pair of nonbonding electrons from a Lewisbase to kind a covalent bond. BF3 thus reactswith Lewis bases such as NH3 to type acid-basecomplexes in which all of the atoms have actually a filled covering ofvalence electrons, as presented in the number below.


The Lewis acid-base theory can additionally be offered to explain whynonmetal oxides such together CO2 dissolve in water to formacids, such together carbonic acid H2CO3.

CO2(g) + H2O(l)

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


One the the oxygen atoms in theintermediate created when water is included to CO2 carriesa confident charge; an additional carries a negative charge. After ~ an H+ion has actually been moved from among these oxygen atom to theother, all of the oxygen atoms in the compound are electricallyneutral. The net result of the reaction in between CO2and water is because of this carbonic acid, H2CO3.

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Practice trouble 9:

Predict whether the complying with ions or molecules have the right to act as either a Lewis acid or a Lewis base.