最新双原子分子初级幻灯片.ppt

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1、Molecular orbital theory and diatomic molecules 分子轨道理论和双原子分子Molecular orbital theory 分子轨道理论 a. Every electron in a molecule is in an average potential field of the nuclei and the other electrons. 每个电子围绕原子核和其他电子组成的平均势场中运动 2. The characteristic distribution and classification of molecular orbital b. -

2、orbital and -bond -轨道与-键 原子轨道平行或原子轨道平行或“肩并肩肩并肩”重叠；重叠；重叠部分对通过一个键轴的平面具有镜面反对称性；重叠部分对通过一个键轴的平面具有镜面反对称性；轨道重叠程度比轨道重叠程度比 键小，键能也小。键小，键能也小。2. The characteristic distribution and classification of molecular orbital b. -orbital and -bond -轨道与-键 3. The structure of homonuclear diatomic molecules 同核双原子分子结构a. The

3、 ground state electronic configurations 基态电子组态The aufbau (building-up) principle in molecules:l Pauli exclusion principle Pauli不相容原理l The minimum energy priciple 能量最低原理l Hunds rule. Hund规则HEnergyHH21s1sY+=1gY-=1*uH2 = 1g2Bond orders:b =12(n n*)n: Electrons in bonding orbitals 成键n*:Electrons in antib

4、onding orbitals反键Diatomic molecules: The bonding in He2He also has only 1s AO, so the MO diagram for the molecule He2 can be formed in an identical way, except that there are two electrons in the 1s AO on He.HeEnergyHeHe21s1s1g1*u The bond order in He2 is (2-2)/2 = 0, so He2 may not exist as a coval

5、ently bounded molecule. However the cation He2+, in which one of the electrons in the * MO is removed, would have a bond order of (2-1)/2 = , so such a cation might be predicted to exist. The electron configuration for this cation is:He2+ = 1g21u*1Diatomic molecules: Homonuclear Molecules of the Sec

6、ond PeriodThe bond order in Li2 is (4-2)/2 = 1, so the molecule could exists. In fact, a bond energy of 105 kJ/mol has been measured for this molecule.LiEnergyLiLi21s1s1g1*u2s2s2g2*uThe bond order in Be2 is (4-4)/2 = 0, so the molecule can not exist as a covalently bounded molecule.BeEnergyBeBe21s1s

7、1g1*u2s2s2g2*uDiatomic molecules: Homonuclear Molecules of the Second PeriodThis produces an MO over the molecule with a node between the F atoms. This is thus an antibonding MO of *u symmetry.Diatomic molecules: The bonding in F22pzA+2pzBThe combinations of symmetry:This produces an MO around both

8、F atoms and has the same phase everywhere and is symmetrical about the F-F axis. This is thus a bonding MO of g symmetry.2pzA-2pzB3g3*uThis produces an MO over the molecule with a node on the bond between the F atoms. This is thus a bonding MO of u symmetry.Diatomic molecules: The bonding in F22pyA+

9、2pyBThe first set of combinations of symmetry:1uThis produces an MO around both F atoms that has two nodes: one on the bond axis and one perpendicular to the bond. This is thus an antibonding MO of *g symmetry.-2pyA2pyB1*gFEnergyFF22s2s1g1*u2p2p2g2*u1u1*g(px,py)pzO2: KK(2s)2 (*2s)2 ( 2p)2 ( 2p)4 ( *

10、2p)2 F2: KK(2s)2 (*2s)2 (2p)2 ( 2p)4 ( *2p)4 For oxygen and fluorine, 2p and 2s are well separated.Molecular Orbital TheoryN2: KK(1g)2 (1u)2 (1 u)4 (2g)2 BEnergyBB22s2s1g1*u2p2p2g2*u1u1*g(px,py)pzHOMOLUMOThe effect of interactions between 2s and 2p. At the start of the second row Li-N, we have mixin

11、g of 2s and 2p. The result is that 1u* is pushed down in energy whereas 2g is raised.B2: KK(1g)2 (1u)2 (1 u)2H2 2 (g1S)2 He2+ 3 (g1s)2 (u1s)1 Li2 6 KK(1g)2 B2 10 KK(1g)2 (1u)2 (1u)2 C2 12 KK(1g)2 (1u)2 (1u)4 N2+ 13 KK(1g)2 (1u)2 (1u)4 (2g)1 N2 14 KK(1g)2 (1u)2 (1u)4 (2g)2 O2+ 15 KK(g2s)2 (u2s)2 (g2p

12、)2 (u2p)4 (g2p)1 O2 16 KK(g2s)2 (u2s)2 (g2p)2 (u2p)4 (g2p)2 F2 18 KK(g2s)2 (u2s)2 (g2p)2 (u2p)4 (g2p)4 Electronic configurations2s-2pz mixingDiatomics MoleculeLi2Be2B2C2N2O2F2Ne2 Bond Order10123210Bond Length ()2.67 n/a1.591.24 1.01 1.21 1.42 n/aBond Energy (kJ/mol)105n/a289609941494155n/aDiamagneti

13、c (d)/ Paramagnetic (p)dn/apddpdn/aBond orders:b =12(n n*)2s-2pz mixing3. The structure of hetronuclear diatomic molecules 异核双原子分子组成分子轨道的原子轨道满足： * 能量相近 * 对称性匹配 * 轨道最大重叠 Example: HFThe F (2s) is much lower in energy than the H (1s) so they do not mix. The F (2s) orbital makes a non-bonding MO. We cer

14、tainly dont have to worry about the F (1s) because is MUCH lower in energy.The H (1s) and F (2p)s are close in energy and do interact. The 2px and 2py dont have the appropriate symmetry though and therefore form nonbonding MOS Only the 2pz and 1s mix.K(2)2 (3)2 (1)4LiH4K(2)2BeH5K(2)2 (3)1CH7K(2)2 (3

15、)2 (1)1NH8K(2)2 (3)2 (1)2OH9K(2)2 (3)2 (1)3HF10K(2)2 (3)2 (1)4MO diagram for HFF2pF2sH1s2314Mainly HMainly FExclusively FABzyAyBxAxB2p2puggu2s2sgu1s1sguABzyAyBxAxB2s2s2p2pBeO 12KK(3)2 (4)2 (1)4CN13KK(3)2 (4)2 (1)4 (5)1CO14KK(3)2 (4)2 (1)4 (5)2NO15KK(3)2 (4)2 (1)4(5)2 (2)1等电子规则等电子规则: The MOs bond for

16、mation and electronic configurations are similar among the isoelectronic diatomic molecules.CO is isoelectronic with N2.KK(3)2 (4)2 (1)4 (5)2 2s2s2p2pLiH4K(2)2BeH5K(2)2 (3)1CH7K(2)2 (3)2 (1)1NH8K(2)2 (3)2 (1)2OH9K(2)2 (3)2 (1)3HF10K(2)2 (3)2 (1)4BeO , BN12KK(3)2 (4)2 (1)4CN ,BeF13KK(3)2 (4)2 (1)4 (5)1CO14KK(3)2 (4)2 (1)4 (5)2NO15KK(3)2 (4)2 (1)4 (5)2 (2)1Molecule electrons electronic configurationEnergy2s2s1g1u2p2p2g2u1u1gpzHOMOLUMOCO is isoelectronic with N2. KK(3)2 (4)2 (1)4 (5)22s2s2p2p30 结束语结束语