上海交通大学：《大学化学》教学资源_加州理工课件学习_Series09MolecularOrbitals

Molecular Orbital Theory Reading:Gray:(2-5),(2-6),(3-1)to(3-6) OGC:(6.1)and(6.2)

Molecular Orbital Theory Reading: Gray: (2-5), (2-6), (3-1) to (3-6) OGC: (6.1) and (6.2) IX-1

Molecular Orbital Theory MO-LCAO:Molecular Orbital-Linear Combination of Atomic Orbitals Lewis Dot Structures don't work for excited states;sometimes they don't even predict the ground state accurately: Example:O2 expected Lewis Dot Structure: Q=9 Actually O2 has two unpaired electrons;this cannot be predicted with Lewis Dot Structures,but it can be predicted with MO-LCAO IX-2

Molecular Orbital Theory MO–LCAO: Molecular Orbital–Linear Combination of Atomic Orbitals Lewis Dot Structures don’t work for excited states; sometimes they don’t even predict the ground state accurately: Example: O2 expected Lewis Dot Structure: O O Actually O2 has two unpaired electrons; this cannot be predicted with Lewis Dot Structures, but it can be predicted with MO-LCAO IX-2

MO-LCAO Lewis Dot Structures tell us: H2 H;H * H·H H," H&H。 MO-LCAO will tell us: a.their local stabilities b.their bond orders and their trend in bond lengths c.their magnetic properties IX-3

MO-LCAO Lewis Dot Structures tell us: H2 + H2 - H H H H H H MO-LCAO will tell us: a. their local stabilities b. their bond orders and their trend in bond lengths c. their magnetic properties H2 IX-3

Nobel Prize,Chemistry,1966 Robert S.Mullikan "For his fundamental work concerning chemical bonds and the electronic structure of molecules by the molecular orbital method" IX-4

Nobel Prize, Chemistry, 1966 ”For his fundamental work concerning chemical bonds and the electronic structure of molecules by the molecular orbital method" Robert S. Mullikan IX-4

Energy dependence on inter-atomic distance indicates the direction of dominating forces ro region where most likely distance electrons start being atr=,E=0;the nuclei repel for a bond (lowest pulled to the other atoms don't interact energy point) atom's nucleus IX-5

Energy dependence on inter-atomic distance E 0 r r 0 region where nuclei repel most likely distance for a bond (lowest energy point) electrons start being pulled to the other atom’s nucleus at r = ∞, E = 0; the atoms don’t interact indicates the direction of dominating forces IX-5

H2 Molecule equilibrium bond distance To electron density in a molecular orbital IX-6

H2 Molecule electron density in a molecular orbital r0 equilibrium bond distance IX-6

Linear Combinations of Atomic Orbitals Molecular orbitals are built up from linear combinations of atomic orbitals: Ha Hp Ψbt 十 0 0 Ip IX-7

Ha Ψa r 0 a Hb Ψb r 0 b Linear Combinations of Atomic Orbitals Molecular orbitals are built up from linear combinations of atomic orbitals: IX-7

The Wavefunctions of two Separate Hydrogen Atoms Ψ Ha + + + Hp + + + + + + + + + + + + IX-8

Ψ Ha + Hb + + + + + + + + + + + + + + + The Wavefunctions of two Separate Hydrogen Atoms IX-8

Orbitals Start to Overlap as Atoms Approach + + × + + ×● + + ×● + + × + + + + + ×● + × ×● + X + X-9

+ + + + + + + + + + + + + + + + Orbitals Start to Overlap as Atoms Approach + + + + + + + + + + + + + + + + IX-9

Wavefunction of H2 Molecule in Ground State Ψ ++ + + × + + Bonding Orbital:(1sa +1sp)=1op 1X-10

Ψ Bonding Orbital: Ψ(1sa + 1sb) = 1σb Wavefunction of H2 Molecule in Ground State + + + + + + + + + + + + + + + + IX-10