《无机化学 Chemical Theory》课程教学资源（讲稿）Part I Basic concepts of Quantum mechanics Chapter 8 Diatomic molecules

What's a chemical bond?Chemical bondingoccurs whenoneormoreelectrons aresimultaneously attractedto two nuclei

What’s a chemical bond? Chemical bonding occurs when one or more electrons are simultaneously attracted to two nuclei

"SOMETIMESITSEEMStomethatabondbetweentwoatomshasbecome so real, so tangible, so friendly,that I can almost see it. ThenI awake with a little shock, for a chemical bond is not a real thing. Itdoes not exist. No one has ever seen one. No one ever can. It is afigment of our own imagination."--C.A.Coulson (1910-1974)Charles CoulsonThemolecular orbitaltheorythat Coulsondeveloped isanBorn13December 1910Dudley, Englandextensionofatomicquantumtheoryanddealswith'allowed'Died7January 1974 (aged63)Oxford, EnglandstatesofelectronsinassociationwithtwoormoreatomicnucleiNationalityBritishtreating a molecule as a whole.He was thus ableto explainFieldsMathematics,Chemistry.PhysicsproperlyphenomenasuchasthestructureofbenzeneandotherInstitutionsUniversityof OxfordKings College Londonconjugated systems,and invokedwhat he calledpartial valencytoAlma materUniversity of Cambridgeaccountforthebondinginsuchcompoundsasdiborane.DoctoralSir John Lennard-JonesadvisorHewrotethreebest-sellingbooks:Waves1941,Electricity1948,andValence1952

"SOMETIMES IT SEEMS to me that a bond between two atoms has become so real, so tangible, so friendly, that I can almost see it. Then I awake with a little shock, for a chemical bond is not a real thing. It does not exist. No one has ever seen one. No one ever can. It is a figment of our own imagination.” -C.A. Coulson (1910-1974) The molecular orbital theory that Coulson developed is an extension of atomic quantum theory and deals with 'allowed' states of electrons in association with two or more atomic nuclei, treating a molecule as a whole. He was thus able to explain properly phenomena such as the structure of benzene and other conjugated systems, and invoked what he called partial valency to account for the bonding in such compounds as diborane. He wrote three best-selling books: Waves 1941, Electricity 1948, and Valence 1952

Quantum mechanical theory for chemical bonding. Molecular Orbital (MO) Theorya)Proposed by Hund, Mulliken, Lennard-Jones et al. in 1930sb)Furtherdevelopments by Slater,Huckeland Popleetalc)MO-based softwares arewidely used nowaday, e.g.,Gaussian.ValenceBond (VB)Theorya) Proposed by Heitler and London 193Os, further developments by Pauling and Slater et alb) Programmed in later 1980s, e.g., latest development--XMVB!.DensityFunctionalTheorya) Proposed by Kohn et al.b) DFT-implemented QM softwares are widely used, e.g., ADF

• Molecular Orbital (MO) Theory a) Proposed by Hund, Mulliken, Lennard-Jones et al. in 1930s. b) Further developments by Slater, Hückel and Pople et al. c) MO-based softwares are widely used nowaday, e.g., Gaussian • Valence Bond (VB) Theory a) Proposed by Heitler and London 1930s, further developments by Pauling and Slater et al. b) Programmed in later 1980s, e.g., latest development-XMVB! • Density Functional Theory a) Proposed by Kohn et al. b) DFT-implemented QM softwares are widely used, e.g., ADF. Quantum mechanical theory for chemical bonding

The discovery of the covalent bond and theconcept of electronpairsHe introduced the notions of electron-pair bonding and the octet ruleThe Cubical Atom.A number ofyears ago,to account forthestriking factwhich has becomeknown as Abegg's law of valence and countervalence,and accordingto which the total difference between the maximum negative and posi-tivevalencesor polarnumbersofan elementisfrequentlyeightandisin no casemore than eight, I designed whatmaybe called the theory ofthe cubical atom.This theory,while it has become familiar to n num-ber of my colleagues,hasnever been published,partlybecauseitwas inmany respects incomplete.Although manyof theseelementsof incom-pletenessremain,and aithotighthetheorylacksto-daymuch ofthenoveltywhich it originally possessed,it seems to me more probable intrinsicallythan some of the other theories of atomic structure which have becen pro-posed, and I cannot discuss more fully the nature of the differences be.veenpolar and nonpolar compoundswithouta briefdiseussionof thisG. N. Lewistheor国nominated 41timesforNobelprizeLBeBTheAtomandtheMoleculeJACS.1916.38.762The covalent bond consists of a shared pair of electrons

G. N. Lewis He introduced the notions of electron-pair bonding and the octet rule. The Atom and the Molecule JACS, 1916, 38, 762 The covalent bond consists of a shared pair of electrons The discovery of the covalent bond and the concept of electron pairs nominated 41 times for Nobel prize

"covalence"The term"covalence"in regard tobonding is proposed firstly一?Electron from hydrogeneElectronfromcarbonI.LangmuirTheArrangement of Electrons inAtomsand Molecules.JACS.1919.41.868-934

I. Langmuir The Arrangement of Electrons in Atoms and Molecules. JACS, 1919, 41, 868–934 The term "covalence" in regard to bonding is proposed firstly “covalence

The naissance of VB and quantum chemistryHL-WavefunctionE:HHb41W.HeitlerF.LondonZeits.fur Physik.44, 455(1927)InteractionBetweenNeutral Atoms and HomopolarIn 1927 theHeitler-London theory was formulated to show how twohydrogen atomwavefunctions join together, with plus, minus, and exchange terms, to form a covalent bond

Zeits. für Physik. 44, 455 (1927). Interaction Between Neutral Atoms and Homopolar W. Heitler F. London In 1927 the Heitler–London theory was formulated to show how two hydrogen atom wavefunctions join together, with plus, minus, and exchange terms, to form a covalent bond. The naissance of VB and quantum chemistry

Thecontributions ofPaulingAO@BOsBACBAL.PaulingPaulingconstructedageneralquantumchemicaltheoryforpolyatomicmolecules.Hedevelopedthenotionofhybridization,thecovalent-ionicsuperposition,andtheresonatingbenzenepictureTheNatureoftheChemicalBond,CornellUniversityPress,IthacaNewYork,1939(3rdEdition,1960)

The Nature of the Chemical Bond, Cornell University Press, Ithaca New York,1939 (3rd Edition, 1960). L. Pauling A B A B A B A B Pauling constructed a general quantum chemical theory for polyatomic molecules. He developed the notion of hybridization, the covalent-ionic superposition, and the resonating benzene picture. The contributions of Pauling

Classical VB theoryThe pair bonding ideas of LewisThe Heitler-London theoryResonance(1928)Hybrid orbitals (1930)

 The pair bonding ideas of Lewis  The Heitler–London theory  Resonance (1928)  Hybrid orbitals (1930) Classical VB theory

Molecular orbital theoryOriginally called the Hund-Mulliken theory, introduced byMullikenin1932.J.C. Slater:F.Hund: J.Lennard-Jones...Thefirstaccurate calculation of a molecular orbitalwavefunction was that made in 1938 on the hydrogenmoleculeR.S.MullikenFrom 1950s

R. S. Mulliken J. C. Slater; F. Hund; J. Lennard-Jones. Molecular orbital theory Originally called the Hund-Mulliken theory, introduced by Mulliken in 1932. The first accurate calculation of a molecular orbital wavefunction was that made in 1938 on the hydrogen molecule. From 1950s

共振论与化学键概念直接联系，成功地应用到所有化学结构和所有化学问题L.Pauling, TheNatureoftheChemical Bond, Cornell University,Press, IthacaNewYork,1939(3rdEdition,1960)G.W.Wheland,ResonanceinOrganicChemistry,Wiley,NewYork,1955相反地，MO理论直接与已有的化学思想概念抵触VB理论统治着人们对化学的理解

共振论与化学键概念直接联系，成功地应用到所有化学结构和所有化学问题 L. Pauling, The Nature of the Chemical Bond, Cornell University, Press, Ithaca New York, 1939 (3rd Edition, 1960). G.W. Wheland, Resonance in Organic Chemistry，Wiley, New York, 1955. 相反地，MO理论直接与已有的化学思想概念抵触 VB理论统治着人们对化学的理解