化学专业英语《Chemistry English》课程教学资源（PPT课件）Lecture 04

natureARTICLESchemistryPUBLISHEDONLINE:29JANUARY2012DOI:10.1038/NCHEM.1263QuadruplebondinginC,andanalogouseight-valenceelectronspeciesSasonShaiki*,DavidDanovich,WeiWu2,Peifeng Su2,HenryS.RzepaandPhilippeC.HibertyTriple bonding is conventionally considered to be the limit for multiply bonded main group elements,despite highermetal-metal bondorders beingfrequentlyobservedfortransitionmetalsand lanthanides/actinides.Here,usinghigh-levetheoretical methods,we show that C2 and its isoelectronic molecules CNBN and CB(each having eight valenceelectrons)areboundbyaquadruplebond.Thebondingcomprisesnotonlyone(randtwo-bonds,butalsooneweakinverted'bond, which canbe characterized bythe interaction of electrons intwo outwardlypointing sphybrid orbitals.Asimpleway of assessingtheenergy of the fourth bond is proposed and is foundto be ~12-17kcalmol-1fortheisoelectronic species studied,and thus stronger than a hydrogen bond. In contrast, the analogues of C that containhigher-rowelements, suchas Si,andGez,exhibitonlydoublebonding.b:C=C:1ECC2三CC31

1

1367April,1931THENATUREOFTHECHEMICALBOND[CONTRIBUTION FROM GATES CHEMICAL LABORATORY, CALIFORNIA INSTITUTE OFTECHNOLOGY,NO.280]THE NATURE OFTHE CHEMICALBONDAPPLICATIONOFRESULTSOBTAINEDFROMTHEQUANTUMMECHANICSANDFROMATHEORYOFPARAMAGNETIC SUSCEPTIBILITYTO THE STRUCTUREOFMOLECULESBY LINUS PAULINGPUBLISHEDAPRIL6,1931RBCEIVEDFEBRUARY17,I931During the last four years the problem of the nature of the chemicalbond has been attacked by theoretical physicists, especially Heitler andLondon, by the application of the quantum mechanics. This work hasled to an approximate theoretical calculation of the energy of formation andof other properties of very simple molecules, such as Ha, and has also pro.vided a formal justification of the rules set up in 1916 by G.N. Lewis forhis electron-pair bond.In the following paper it will be shown that manymore results of chemical significance can be obtained from the quantummechanical equations, permitting the formulation of an extensive andpowerful set of rules for the electron-pair bond supplementing those ofLewis. These rules provide information regarding the relative strengths2

2

Statement byLinus Pauling about themanuscript on thenatureof thechemical bond6August1979During my early years as a scientist, beginning in i919,I had a special interestintheproblem of the natureof the chemicalbond; that is, the nature of the forces that hold atoms together inmolecules,crystals, and other substances,Much of my work duringthis early period was directed toward a solution of this problem, byapplication of both experimental and theoretical methods,Assoon asquantum mechanics was discovered, in 1925,I began striving to applythis powerful theory to the problem.I published several theoreticalpapers in this field during the next few years, without, however,having been ableto answeranumber of important questions.Thenone evening.inDecember,1930,whileIwas sitting atmydeskinmy study at our home on Arden Road and California Street, in Pasadena,California,I had an idea about a way to simplifythe quantum-mechanicalequations in such a manner as to permit their easy approximate solution.I was so excited about this idea that I stayed up most of the night,applying theideatovariousproblems,During the next two months I continued to work on this ideaand to write a paper communicating the results of its application tothe problem of the nature of the chemical bond.As I recall, themanuscript to which this is an introduction was written in early February.1931.A typescriptwas prepared from it,and the manuscript was putinthe wastepaper basket, presumably by me, although I do not have a clearmemory of this matter.Forty-seven years later the manuscript wasgiven to mebyProfessor Ralph Hultgren,In193l Ralph Hultgren wasone of mygraduate students,working for his Ph.D.in chemistry.Hestated, when he gave me themanuscript, that he had removed it fromthe wastepaper basket and had kept it for the intervening forty-sevenyears.I made some changes in the typescript, and the revisedtypescript was submitted to the editor of the Journal of the AmericanChemical Societyon17February193l,Itwas published in theApril3issue,whichappearedon6April1931,onpages1367to1400of theJournal of the American Chemical Society.Volume 53.The short

3

time that elapsed between receipt of the article and publication in theJournal indicates thatthe Editor of the Journal,Professor Arthur B, Lambof Harvard University,did not go through the usual process of submittingthe paper to referees for criticism,but instead decided that itwasproper for itto be sent immediately to the printer.There are a few differences between the manuscript andthe published paper.The only major ditference is that I removed thesection on the single-electron bond, pages 4 to 7 of the manuscript,before submitting the typescript for publication,This section on thesingle-electron bond was later expanded, and was published as aseparate paper, with the title The Nature of the Chemical Bond. IL. TheOne-Electron Bond and the Three-Electron Bond. Journal of the AmericanChemicalSociety53,3225-(a931).Duringthefollowingtwoyearsfive more papers were published with the title "The Nature of theChemical Bond, IIl, IV, V, I, and VII, in the Journal of the AmericanChemical Society and the Journal of Chemical PhysicsThese seven papers, and especially the first one, for whichthe original manuscript has been preserved, constituted the principalbasis of knowledge for my bookTheNature of the Chemical Bond,thefirstedition of which was published by Cornell University Press in lssg(secondedition1940,third edition1960).This193lpapermightwellbeconsideredthemost importantpart of the workforwhichI was awardedtheNobel Prizein Chemistryin1954

4

5

5

1365April,1931THE CONSTRUCTION OFDEWAR FLASES[CONTRIBUTION VROMTHEDEPARTMENTOF CHEMISTRY OPTHE UNIVERSITY OPILLINOIS]THECONSTRUCTIONOFDEWARFLASKSBYT.E.PHIPPS,M.J.COPLEYANDE.J.SHAWRECEIYEDFaRRUARY10,1931POBLISED APRIL 6, 1931Amethod of making PyrexDewarflasks of considerablecapacityhasbeen developed which may be of interest to somewho have a limited orintermittentsupply of liquid air.Themost convenient size,in view of thelimited sizes of Pyrex flasks, is probablythree liters.The outerwall ismadeofa 5-liter fask.If 7-or S-liter flasks wereavailable,5-literDewarscould be constructed.However, with a 12-liter outer flask, silvering be-comes rather dificult, and the resulting flask is too bulky to bepractical.A heavy-walled 16-mm. tube, E in the figure, is sealed to the base of theneck of a 5-liter round-bottomed fiask.The heavy ring at the top of theneck is then cut off as closely as possible and the flask cut in two partsaround a great circle perpendicular totheaxis of theneck.The crack is shownatB.It ismadeby scratching a fileFEmark about an inch long on the flask,wrapping one turn of No.22 chromelAwire about the flask, and heating with acurrent of 10-12 amp.until the glass isfelt tobe warm 6-8mm.from thewire.Afewcc.of water is poured on the fileBmark.The crack obtained is often so-CCsmooth that there is dificulty in deter.mining therelativepositions previous tocracking.The inner fiask is preparedby cutting off the neck of a 3-liter flaskas closely as possible to the base of theFig.1.neck,A,and sealing on a previouslyfiared 40-mm.heavy-walled tube.This is then cut off so that it extendsthrough the neck of the outer fiask a distance about equal to that betweenthe walls of the neck.Thebottom half of the outer flask is placed in an asbestos-covered ironring.Aring ofbrass,D,such as a 20-mm.length of a 70-mm.brass tube isthen placed in the glass hemisphere, and the inner flask is set on it.Theupper half of the outer flask is put in place and clamped down with anotherasbestos-covered iron ring.The Dewar seal at thetop is then made usingtwo hand torches, one witha large air-gas fame,the other with a moderate6air-oxygen-gas flame,Obviouslythis must be done at a rather hightemperature, since the inner flask is essentially unstable.Blowing can bedone through the evacuating tube, but is usually unnecessary

6

Phases or states of matterPhases or states of matter:The physical properties of solids, liquids, and gasesCHANGINGSTATEgascooing:particleslosingkineticenerayandsiowingdowngas condensing:particleslosingpotentialenergyandgettingcloserliquldcoong:particies losingTCK.E.andslowingdownliguid freezing:particles losingb.p.PE.andgettingclosersolidcooling1.p/m.p.freezingcompletefreezingbeginscondensingbeginscondensingcompleteTime7

7 Phases or states of matter The physical properties of solids, liquids, and gases Phases or states of matter:

Phases or states of matterLIOUIDSThe particles in a liquid are fairly well ordered over a shortdistance, but there is no long range order.The particles have more kinetic energy than in the solid state andit is this movement of the particles that disrupts the arrangementof the lattice.The potential energy of the particles is also greater than in solidsbecause they have moved apart slightly.At room temperature most substances which are liquid are:. covalently bonded molecular substances with quite strong vander Waals forces (large molecules with lots of electrons) orhydrogen bonded liquids such as water and alcohols.In an ideal liquid the behavior of a particle depends only on thenumber of other particles around it and not on their identityLiquid mixtures which behave in this way are said to obey8Raoult'slaw

8 Phases or states of matter The particles in a liquid are fairly well ordered over a short distance, but there is no long range order. The particles have more kinetic energy than in the solid state and it is this movement of the particles that disrupts the arrangement of the lattice. The potential energy of the particles is also greater than in solids because they have moved apart slightly. At room temperature most substances which are liquid are: ● covalently bonded molecular substances with quite strong van der Waals forces (large molecules with lots of electrons) or ● hydrogen bonded liquids such as water and alcohols. In an ideal liquid the behavior of a particle depends only on the number of other particles around it and not on their identity. Liquid mixtures which behave in this way are said to obey Raoult’s law. LIQUIDS

Phases or states of matterSOLIDSThe particles in a solid are arranged in an ordered latticeThe kinetic energy of the particles is low and they vibrate abouttheirlattice position.As the solid is heated the particles move moreand the lattice expands becoming more disordered.The potential energy of the particles is also low because they areclose together.9

9 Phases or states of matter The particles in a solid are arranged in an ordered lattice. The kinetic energy of the particles is low and they vibrate about their lattice position. As the solid is heated the particles move more and the lattice expands becoming more disordered. The potential energy of the particles is also low because they are close together. SOLIDS

Phases or states of matterSolids may be bonded in different ways.In metalsThe lattice energy depends on the charge on the metallic ions, thesize of theions, and the type of lattice.In ionic solidsThe lattice energy depends on the charge on the ions, the size of theions, and the type of lattice.In covalently bonded macromolecular solidsThe bond energy depends on the size of the atoms and thearrangement of the lattice.In covalentlybonded molecular solidsThe lattice energy depends on the forces between the molecules.These can be hydrogen bonds in compounds where hydrogen isbonded to nitrogen, oxygen, or fluorine (e.g. H,O); dipole forceswhere there is charge separation (e.g. CO2); van der Waals forceswhich depend on the number of electrons (e.g. noble gases)..10

10 Phases or states of matter Solids may be bonded in different ways: In metals The lattice energy depends on the charge on the metallic ions, the size of the ions, and the type of lattice. In ionic solids The lattice energy depends on the charge on the ions, the size of the ions, and the type of lattice. In covalently bonded macromolecular solids The bond energy depends on the size of the atoms and the arrangement of the lattice. In covalently bonded molecular solids The lattice energy depends on the forces between the molecules. These can be hydrogen bonds in compounds where hydrogen is bonded to nitrogen, oxygen, or fluorine (e.g. H2O); dipole forces where there is charge separation (e.g. CO2 ); van der Waals forces which depend on the number of electrons (e.g. noble gases)