复旦大学：《普通化学 General Chemistry》课程教学资源（课堂讲义）Chap 4 - Molecular Orbital Method of Chemical Bonding, and Molecular

PaRT 4- Molecular Orbital method of Chemical Bonding and molecular Interactions Reference: Chapter 10 in textbook

1 PART 4 – Molecular Orbital Method of Chemical Bonding, and Molecular Interactions Reference: Chapter 10 in textbook

Molecular Orbital(MO)Method MO method Molecular orbitals are formed by combination of atomic orbitals of bonding atoms of total mos a f of total atomic orbitals All es belong to the molecule, not original atoms Electrons are filled based on the same criteria as in atomic orbitals:Pauli exclusion principle; (i Filled from the lowest energy first, (Ground State)

Molecular Orbital (MO) Method  MO method  Molecular orbitals are formed by combination of atomic orbitals of bonding atoms;  # of total MOs = # of total atomic orbitals;  All e’s belong to the molecule, not original atoms.  Electrons are filled based on the same criteria as in atomic orbitals: (i) Pauli exclusion principle; (ii) Filled from the lowest energy first, (Ground State). 2

Molecular Orbital(MO)Method Bonding, Antibonding, Nonbonding MOS Bonding Mo: W/energy lower than origianl Ao Antibonding MO: W/ energy higher than original Ao Nonbonding MO: W/energy equal to orignal ao; of bonding Mo=# of antibonding MO (P2 3

Molecular Orbital (MO) Method  Bonding, Antibonding, Nonbonding MOs  Bonding MO: w/ energy lower than origianl AO;  Antibonding MO: w/ energy higher than original AO;  Nonbonding MO: w/ energy equal to orignal AO;  # of bonding MO = # of antibonding MO. 3

Homonuclear diatomic molecules Bond Order=0.5* bonding e-# antibonding e) Larger bond order More stable molecule When bond order =0. it means this molecule cannot exist Example: 1st period elements 01s H H H He He He Q: EXplain(1)why H2, He2 t ions can exist?(2) What is the bond order of these ions

Homonuclear Diatomic Molecules  Bond Order = 0.5 * (# bonding e – # antibonding e)  Larger bond order ↔ More stable molecule  When bond order = 0, it means this molecule cannot exist. Example: 1st period elements  Q: Explain (1) why H2 - , He2 + ions can exist? (2) What is the bond order of these ions? 4 H H2 H He He2 He

MO of Li2 and Be2 2s 02s 01s 01s Is Is Is 12 Be B Ground State Electron Configuration in MO Li2:(σ1)2(os)2(a2s Be2:(σ1)2(o1)2(2)2(o23)2 Li,: KK(o2) Be2:KK(σ2)2(2

MO of Li2 and Be2 5 Ground State Electron Configuration in MO Li2 :（σ1s)2（σ1s *)2 （σ2s)2 Be2 :（σ1s)2 （σ1s *)2 （σ2s)2 （σ2s *)2 Li2 : KK（σ2s)2 Be2 : KK（σ2s)2 （σ2s *)2

2nd Period Homonuclear molecules Molecules Electron configuration Bond order Bond length Bond energy (pm) (kJmol-1) KK o2s)2 108 Be2KK(a2)2(2)2 0 245 B2 KK(o2s)2(o2s )2(T2p) 2 159 289 C2KK(a2)2(2)2(T2) 124 599 KK(o2)2(23)2(兀2p)4(a2p)2 110 942 O2KK(o2)2(o2)2(a2p)2(m2y)4(x2p 121 F2KK(a2y2(o23)2(2)2(mp)(2p 141 154 6

2nd Period Homonuclear Molecules 6 Molecules Electron configuration Bond order Bond length Bond energy （pm) (kJ⋅mol-1) Li2 KK（σ2s)2 1 267 108 Be2 KK（σ2s)2 （σ2s *)2 0 245 9 B2 KK （σ2s)2 （σ2s *)2（π2p)2 1 159 289 C2 KK （σ2s)2 （σ2s *)2（π2p)4 2 124 599 N2 KK （σ2s)2 （σ2s *)2（π2p)4（ σ 2p)2 3 110 942 O2 KK （σ2s)2 （σ2s *)2（ σ 2p)2（π2p)4 (π2p *)2 2 121 494 F2 KK （σ2s)2 （σ2s *)2（ σ 2p)2（π2p)4 (π2p *)4 1 141 154

MO Energy 十忡十件料世封 2 L: B Energy crossing between O2p and T2n MOs Q: Among the molecules above, (1)Which one is the most stable?(2)Which ones have paramagnetism? 7

MO Energy  Q: Among the molecules above, (1) Which one is the most stable? (2) Which ones have paramagnetism? 7 Energy crossing between σ2p and π2p MOs

Heteronuclear diatomic molecules 丌 p 02 P 丌 p co(ground state): 2 s KK(25)2(a25)2(2n)4(o2p)2 U s Is C Co 8

Heteronuclear Diatomic Molecules 8 CO (ground state): KK（σ2s)2 （σ2s * )2 （π2p)4（σ 2p)2

Heteronuclear diatomic molecules No (ground state): s 2s KK(2)3(2)2(a2p)2(2)2(m2p) Is Is NO

Heteronuclear Diatomic Molecules 9 NO (ground state): KK (σ2s)2(σ2s *)2 (σ 2p)2 (π2p)4 (π2p *)1 N NO O

Heteronuclear diatomic molecules 补书 LiF (ground state) (1s1)2(1s)2(2sp)2(o)2(m)4 Li LIF F

Heteronuclear Diatomic Molecules 10 LiF (ground state): (1sLi)2 (1sF)2 (2sF)2 (σ )2 (πnb)4