Final exam after miterm 3

Final exam after miterm 3 - Other triatomic molecules...

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Unformatted text preview: Other triatomic molecules Triatomic monohydrides are predicted to be linear only if they can be written as a triple bond (HCN, HCP). HNC might be predicted as linear if it is a triplet diradical, and in fact it is linear, but SCF theory is quite clear that the singlet is supposed to be linear and, as actually seen, is lower in energy. Other monohydrides are predicted to be , and are, bent: 2 HCO, 1 HNO, 1 HPO, 1 HCF, 1 HCCl, 1 HSiCl, 3 HSiCl The following triatomic molecules are linear (singlet unless otherwise shown): CCC, SiCC, 2 CCN, 2 CNC, 3 NCN, 2 NCO, 2 NNO+, 2 NNN, 2 OBO, 2 OCO+, OCO, SCS, NNO, OCS, ClF 2- Bent molecules are 2 ONO, FCF, FSiF, OOO, OSO, SSO, ONF, 2 FNF, 2 OClO, ClOCl, ClF 2 + , 2 ClF 2 These can easily be rationalized by the Walsh diagram for three heavy atoms if one assumes that only the top occupied orbitals count, or equivalently, only 17 to 21 valence electrons makes a bent molecule. The 21 electron case is most unclear, but the one electron in the 7a 1 orbital loses to the two next lower orbitals. 1s electrons are not included in these counts or in the drawings at right or on the following slides. Three heavy atoms This slide, taken from last lecture, shows the shape of orbitals with a given symmetry designation (i.e. a 1 , a 2 , b 1 , b 2 for symmetric bent, g , u , g , u for linear, water (along with very approx water orbital energies ). a 2 (not shown) and b 1 are pi orbitals (antibonding and bonding respectively) Orbital out of molecular plane All orbitals in molecular plane Ozone Hartree-Fock 6-31G* Orbital Energies versus angle Note that the orbitals do not become degenerate at 180 degrees because all Pi orbitals are not filled; this makes the x and y orbitals non-degenerate. In OF 2 or CO 2 they should become degenerate. The 1s derived orbitals are not shown in this or the next two slides, and in all three all orbitals lower than -10 E. V. are fully occupied.-7-6-5-4-3-2-1 1 2 3 90 100 110 120 130 140 150 160 170 180 Degrees Energy e. V. Total E + 6100 224+All Occ. Orbitals 41+Top 3 Occ. Orbitals 64 + Mid 3 Occ. Orbitals 114+Bot. 3 Occ. Orbitals-50-40-30-20-10 10 90 100 110 120 130 140 150 160 170 180 Degrees Energy e. V. A1 B1 A1 A2 B2 B1 B2 A1 A1 B2 A1 F 2 O Hartree-Fock 6-31G* Orbital Energies versus angle-8-6-4-2 2 4 6 90 100 110 120 130 140 150 160 170 180 Degrees Energy e. V. Total E + 7438 260 + Al Occ. Orbitals 131 + Top 6 Occ. Orbitals 121 + Bot. 3 Occ. Orbitals As expected certain pairs of orbitals approach degeneracy at 180 degrees. The kinks in the curves are due to a change in occupied orbitals versus angle.-50-40-30-20-10 10 90 100 110 120 130 140 150 160 170 180 Degrees Energy e. V....
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This note was uploaded on 09/22/2011 for the course CHEM 222 taught by Professor Linda during the Spring '11 term at Edmonds Community College.

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Final exam after miterm 3 - Other triatomic molecules...

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