In 1923 G. N. Lewis argued another method of looking at thereaction in between H+ and also OH- ions. In theBrnsted model, the OH- ion is the active species inthis reaction that accepts one H+ ion to kind a covalent bond. In theLewis model, the H+ ion is the energetic speciesitaccepts a pair of electron from the OH- ion to kind acovalent bond.
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In the Lewis concept of acid-base reactions, bases donate pairsof electrons and acids accept pairs of electrons. A Lewis acidis therefore any substance, such together the H+ ion, thatcan accept a pair of nonbonding electrons. In other words, aLewis mountain is an electron-pair acceptor. A Lewis baseis any substance, such as the OH- ion, that deserve to donatea pair that nonbonding electrons. A Lewis basic is as such an electron-pairdonor.
One advantage of the Lewis theory is the way it complementsthe design of oxidation-reduction reactions. Oxidation-reductionreactions involve a move of electron from one atom toanother, through a net adjust in the oxidation variety of one or moreatoms.
The Lewis theory suggests that acids react through bases to sharea pair the electrons, with no change in the oxidation numbers ofany atoms. Countless historicsweetsballroom.comical reactions deserve to be sorted into one or theother of these classes. One of two people electrons room transferred indigenous oneatom to another, or the atoms come together to re-publishing a pair ofelectrons.
The principal benefit of the Lewis concept is the method itexpands the variety of acids and therefore the variety of acid-basereactions. In the Lewis theory, an mountain is any type of ion or moleculethat have the right to accept a pair of nonbonding valence electrons. In thepreceding section, us concluded that Al3+ ion formbonds to 6 water molecule to offer a facility ion.
Al3+(aq) + 6 H2O(l)
This is an example of a Lewis acid-base reaction. The Lewisstructure of water suggests that this molecule has actually nonbondingpairs the valence electrons and also can therefore act as a Lewis base.The electron configuration of the Al3+ ion suggeststhat this ion has empty 3s, 3p, and 3dorbitals that can be used to host pairs that nonbonding electronsdonated by bordering water molecules.
Thus, the Al(H2O)63+ ion isformed as soon as an Al3+ ion acting as a Lewis mountain picksup six pairs of electrons from bordering 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 only three locations in thevalence shell of the boron atom. Together a result, the boron atom is sp2hybridized, which leaves an empty 2pzorbital on the boron atom. BF3 can therefore act together anelectron-pair acceptor, or Lewis acid. It deserve to use the empty 2pzorbital to choose up a pair that nonbonding electrons from a Lewisbase to kind a covalent bond. BF3 therefore reactswith Lewis bases such as NH3 to form acid-basecomplexes in which all of the atoms have a filled covering ofvalence electrons, as displayed in the number below.
The Lewis acid-base concept can additionally be provided to explain whynonmetal oxides such as 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 together anelectron-pair donor, or Lewis base. The electron-pair agree isthe carbon atom in CO2. Once the carbon atom picks upa pair of electron from the water molecule, that no longer needsto form twin bonds through both that the other oxygen atoms together shownin the figure below
One of the oxygen atom in theintermediate formed when water is added to CO2 carriesa hopeful charge; another carries a an adverse charge. ~ an H+ion has been moved from among these oxygen atom to theother, every one of the oxygen atoms in the compound are electricallyneutral. The net result of the reaction between CO2and water is thus carbonic acid, H2CO3.
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|Practice difficulty 9:|
Predict even if it is the adhering to ions or molecules deserve to act together either a Lewis acid or a Lewis base.