无机化学无机化学英文PPT (2).ppt

Molecular orbital：Its a polycentric orbit on the basis of the multiple nucleus Their wave function is also the solution of Schrodinger equation,which can be obtained via linear combination of atomic orbitals.8.5 Molecular orbital theoryMolecule orbital theory(MO method)Molecular orbital Homonuclear diatomic moleculesHetermonuclear diatomic moleculesSymmetry of atomic and molecular orbital The basic points of molecular orbital theory are as follows:(1)n molecular orbitals can be obtained by linear combination of n atomic orbitals.(2)The order of filling electrons in molecular orbitals follows the same rules as atomic orbitals,lowest energy,Pauli incompatibility,and hunt rule Similar energy Symmetry matching Maximum overlap(3)Three principles of bonding:Basic Principle1.Basic conception of MO The electrons in a molecule neither belong to one atom,nor are confined to adjacent atoms,but move in the whole molecular space(different from the valence bond theory),which is nonlocal.The molecular orbital theory was foundedby hunt and maliken.(2)The motion state of electrons in molecular space is named as MO,which is expressed by wave function MO,the probability density and electron cloud of electrons appearing everywhere in the molecule are represented by|2,and the MOs are represented by,(The atomic orbitals are represented by s,p,d,f).(3)Each molecular orbital i has a corresponding Ei,the total molecular energy Etotal=Ei 2.Liner Combination of Atomic Orbitals(1)MOs are originated from linear combinations of atomic orbitals.*M:Anti-Bonding molecular orbital The nuclear probability density decreases and the energy is higher than the atomic orbital.M=C1A+C2B*M=C1A C2BC1,C2:constant,representing contribution of each atomic orbitals to molecular orbitalsM:Bonding molecular orbital The nuclear probability density increases and the energy is lower than the atomic orbital.(2)The number of molecular orbitals linearly combined by atomic orbitals is the same as that of atomic orbitals.(3)Combination Principles Not any atomic orbitals can be combined into MOs,only those satisfying,as follows:Depending on the efficiency of bondingDepending on whether it can be bondedSymmetry matchingSimilar energyMaximum overlapAO can be effectively combined into MO.（1）symmetry Principle depending on whether it can be bonded AO with the same symmetry forms bonding MO,but AO with opposite symmetry forms anti bonding MO.(+)and(+)MO MO=A+B Effective overlap,symmetry matchingInvalid overlap,symmetry mismatchA(+)and(-)*MO *MO=A -A The linear combinations of s orbit and s orbit are the and ss节面s orbitsMOss-p overlap(taken HF as example)Energy level increasing Energy level increasing p-p overlap(taken O2 as example)(a)The linear combination of px-orbitals and px-orbitals through X-axis along with“head to head”.(b)The linear combination of py(or Z)-orbitals and py(or Z)-orbitals through perpendicular to the X-axis along with“shoulder to shoulder”.Energy level increasing The linear combination of p-orbitals and p-orbitals.Two ways:“head to head”and“shoulder to shoulder”.Atomic orbitalsMolecular orbitals head to head Molecular orbitals pass through nodal surfaces which is perpendicular to the X-axis 2pz2pzNodal planeshoulder to shoulderAtomic orbitalsMolecular orbitalsWhen the atomic orbitals overlap,the larger the effective overlap is,the stronger the bonding effect is,correspondingly,the stronger the chemical bond is and the more stable the molecule is(under the conditions of the same symmetry and similar energy).(3)Greatest overlap and similar energy.The quantitative indicator of molecular stability(bond strength)for diatomic molecule is the bond order(B.O)：the difference between the number of bonding electrons and the number of antibonding electrons，divided by 2 (pairs).(4)Bond order(B.O)The meaning of bond order is:it indicates the bond strength between adjacent atoms.The larger the bond order is,the shorter the bond length is,and therefore the greater the bond energy is.If the bond order is equal to zero,it means that the bonding energy and anti bonding energy are offset.The overall effect is not bonding,and the molecule can not exist stably.(Electron numbers of bonding-Electron numbers of anti-bonding)