MO Diagram for Triangular H3 A fragment approach to deriving molecular orbitals 5.03 Inorganic Chemistry + Image from the H3 resource center http://h3plus.uiuc.edu/ MO Diagram for Triangular H3 A fragment approach to deriving molecular orbitals 5.03 Inorganic Chemistry HOMO of the Ammonia Molecule The ammonia HOMO has A1 symmetry This lone pair orbital also involves bonding of N 2pz with the bonding MO of the stretched H3 molecule This MO is responsible for the Lewis base character of the ammonia molecule 5.03 Inorganic Chemistry HOMO of the Ammonia Molecule The ammonia HOMO has A1 symmetry This lone pair orbital also involves bonding of N 2pz with the bonding MO of the stretched H3 molecule This MO is responsible for the Lewis base character of the ammonia molecule 5.03 Inorganic Chemistry HOMO of the Ammonia Molecule The ammonia HOMO has A1 symmetry This lone pair orbital also involves bonding of N 2pz with the bonding MO of the stretched H3 molecule This MO is responsible for the Lewis base character of the ammonia molecule 5.03 Inorganic Chemistry HOMO-1 of the Ammonia Molecule The doubly degenerate ammonia HOMO-1 has E symmetry This orbital is the bonding interaction between N 2px ; 2py and the E MOs of stretched H3 5.03 Inorganic Chemistry HOMO-1 of the Ammonia Molecule The doubly degenerate ammonia HOMO-1 has E symmetry This orbital is the bonding interaction between N 2px ; 2py and the E MOs of stretched H3 5.03 Inorganic Chemistry HOMO-3 of the Ammonia Molecule The singly degenerate ammonia HOMO-3 has A1 symmetry This orbital is dominated by N 2s character but spreads out and is bonding with the bonding H3 MO 5.03 Inorganic Chemistry HOMO-3 of the Ammonia Molecule The singly degenerate ammonia HOMO-3 has A1 symmetry This orbital is dominated by N 2s character but spreads out and is bonding with the bonding H3 MO 5.03 Inorganic Chemistry LUMO of the Ammonia Molecule The singly degenerate ammonia LUMO has A1 symmetry and is N-H σ∗ in character 5.03 Inorganic Chemistry MO Diagram for the Ammonia Molecule 5.03 Inorganic Chemistry Summary of Some Key Points MOs are approximated as LCAOs The symmetry of the MOs is that of the irreducible representations Molecules can be analyzed in terms of constituent fragments, e.g. water as O + \stretched H2" Bonding is greater when both the orbital energy match and the spatial overlap is better The more electronegative atom gets the greater share of the bonding combination and vice versa Interaction is identically zero between orbitals belonging to different irreducible representations 5.03 Inorganic Chemistry Summary of Some Key Points MOs are approximated as LCAOs The symmetry of the MOs is that of the irreducible representations Molecules can be analyzed in terms of constituent fragments, e.g. water as O + \stretched H2" Bonding is greater when both the orbital energy match and the spatial overlap is better The more electronegative atom gets the greater share of the bonding combination and vice versa Interaction is identically zero between orbitals belonging to different irreducible representations 5.03 Inorganic Chemistry Summary of Some Key Points MOs are approximated as LCAOs The symmetry of the MOs is that of the irreducible representations Molecules can be analyzed in terms of constituent fragments, e.g. water as O + \stretched H2" Bonding is greater when both the orbital energy match and the spatial overlap is better The more electronegative atom gets the greater share of the bonding combination and vice versa Interaction is identically zero between orbitals belonging to different irreducible representations 5.03 Inorganic Chemistry Summary of Some Key Points MOs are approximated as LCAOs The symmetry of the MOs is that of the irreducible representations Molecules can be analyzed in terms of constituent fragments, e.g. water as O + \stretched H2" Bonding is greater when both the orbital energy match and the spatial overlap is better The more electronegative atom gets the greater share of the bonding combination and vice versa Interaction is identically zero between orbitals belonging to different irreducible representations 5.03 Inorganic Chemistry Summary of Some Key Points MOs are approximated as LCAOs The symmetry of the MOs is that of the irreducible representations Molecules can be analyzed in terms of constituent fragments, e.g. water as O + \stretched H2" Bonding is greater when both the orbital energy match and the spatial overlap is better The more electronegative atom gets the greater share of the bonding combination and vice versa Interaction is identically zero between orbitals belonging to different irreducible representations 5.03 Inorganic Chemistry Summary of Some Key Points MOs are approximated as LCAOs The symmetry of the MOs is that of the irreducible representations Molecules can be analyzed in terms of constituent fragments, e.g. water as O + \stretched H2" Bonding is greater when both the orbital energy match and the spatial overlap is better The more electronegative atom gets the greater share of the bonding combination and vice versa Interaction is identically zero between orbitals belonging to different irreducible representations 5.03 Inorganic Chemistry What are Hypervalent Molecules? Molecules that appear to violate the octet rule by having more than eight electrons in the valence shell − Examples: PCl5, SF6, ClF3,I3 To maintain the primacy of 2c-2e bond (Lewis), use of d orbitals were invoked Alternatively (Pimentel), the 3c-4e bond (MO theory) explains matters 5.03 Inorganic Chemistry What are Hypervalent Molecules? Molecules that appear to violate the octet rule by having more than eight electrons in the valence shell − Examples: PCl5, SF6, ClF3,I3 To maintain the primacy of 2c-2e bond (Lewis), use of d orbitals were invoked Alternatively (Pimentel), the 3c-4e bond (MO theory) explains matters 5.03 Inorganic Chemistry What are Hypervalent Molecules? Molecules that appear to violate the octet rule by having more than eight electrons in the valence shell − Examples: PCl5, SF6, ClF3,I3 To maintain the primacy of 2c-2e bond (Lewis), use of d orbitals were invoked Alternatively (Pimentel), the 3c-4e bond (MO theory) explains matters 5.03 Inorganic Chemistry What are Hypervalent Molecules? Molecules that appear to violate the octet rule by having more than eight electrons in the valence shell − Examples: PCl5, SF6, ClF3,I3 To maintain the primacy of 2c-2e bond (Lewis), use of d orbitals were invoked Alternatively (Pimentel), the 3c-4e bond (MO theory) explains matters 5.03 Inorganic Chemistry Problematic Lewis Diagram of the SF4 Molecule F F S F F 5.03 Inorganic Chemistry Valence Orbital Ionization Energies, eV Atom 1s 2s 2p 3s 3p H 13.6 He 24.6 Li 5.4 Be 9.3 B 14.0 8.3 C 19.4 10.6 N 25.6 13.2 O 32.3 15.8 F 40.2 18.6 Ne 48.5 21.6 S 20.7 11.6 5.03 Inorganic Chemistry Structure of the SF4 Molecule 5.03 Inorganic Chemistry Structure of the SF4 Molecule 5.03 Inorganic Chemistry Structure of the SF4 Molecule 5.03 Inorganic Chemistry Structure of the SF4 Molecule 5.03 Inorganic Chemistry Structure of the SF4 Molecule 5.03 Inorganic Chemistry Electron Density of the SF4 Molecule An 0.15 surface contour is plotted (atomic units) 5.03 Inorganic Chemistry Atomic Charge Distribution in the SF4 Molecule Results from MO Calculation followed by NBO analysis F F S F F Axial S-F bond distances are longer than the equatorial ones More negative charge is accumulated on the axial F atoms The analogous SH4 molecule does not exist! 5.03 Inorganic Chemistry Atomic Charge Distribution in the SF4 Molecule Results from MO Calculation followed by NBO analysis F F S F F Axial S-F bond distances are longer than the equatorial ones More negative charge is accumulated on the axial F atoms The analogous SH4 molecule does not exist! 5.03 Inorganic Chemistry Atomic Charge Distribution in the SF4 Molecule Results from MO Calculation followed by NBO analysis F F S F F Axial S-F bond distances are longer than the equatorial ones More negative charge is accumulated on the axial F atoms The analogous SH4 molecule does not exist! 5.03 Inorganic Chemistry Three-Center Four Electron Bond Advanced by Pimentel and frequently invoked to explain excess of electrons One of the bonding electron pairs becomes ligand-based nonbonding This leads to a bond order of 0.5 for both ligands What is the bond order in SF4? 5.03 Inorganic Chemistry Three-Center Four Electron Bond Advanced by Pimentel and frequently invoked to explain excess of electrons One of the bonding electron pairs becomes ligand-based nonbonding This leads to a bond order of 0.5 for both ligands What is the bond order in SF4? 5.03 Inorganic Chemistry Three-Center Four Electron Bond Advanced by Pimentel and frequently invoked to explain excess of electrons One of the bonding electron pairs becomes ligand-based nonbonding This leads to a bond order of 0.5 for both ligands What is the bond order in SF4? 5.03 Inorganic Chemistry The Sulfur Lone Pair in the SF4 Molecule Natural Bond Orbital (NBO) analysis following MO calculation Composition is 67% s, 33% p 5.03 Inorganic Chemistry The σ Fluorine Lone Pair in the SF4 Molecule Natural Bond Orbital (NBO) analysis following MO calculation Composition is 82% s, 18% p 5.03 Inorganic Chemistry The π Fluorine Lone Pair in the SF4 Molecule Natural Bond Orbital (NBO) analysis following MO calculation Composition is 2% s, 98% p 5.03 Inorganic Chemistry The Axial S{F Bond in the SF4 Molecule Natural Bond Orbital (NBO) analysis following MO calculation The axial S-F bond is very polar with some covalent character The sulfur d contribution to this bonding orbital is only ca.