W2013CHM2311 Part 3a Notes

A neither b both c only xef2 d only sf2 why

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Unformatted text preview: lane which contains the principal axis and bisects 2 Cn axes. Improper Axis Sn Rotate the molecule by 360/n degrees around the improper axis and then reflect the molecule through the plane perpendicular to the improper axis Inversion center i Invert the molecule through the inversion center Exercise: Iden0fy all symmetry elements/opera0ons for the following molecules: SOFCl H2O2 PCl5 H2N2 NOCl ethane  ­ staggered trans ­C4F2Cl2H4 H3N Which of the following molecules has a C3 rota.on axis? BF3 vs ICl3 Which of these two molecules has a C4 rota.on axis? SF4 vs XeF4 PF5 vs BrF5 Which of these two molecules has an inversion center? BeF2 vs OH2 Prac.ce Problems: Does either of the two molecules BrF5 or AsF5 have a 3 ­fold rota0on axis (C3)? (a) neither (b) both (c) only BrF5 (d) only AsF5 Does either of the two molecules PH3 or GaH3 possesses a 2 ­fold rota0on axis (C2)? (a) neither (b) both (c) only GaH3 (d) only PH3 Does either of the two molecules SF2 or XeF2 possess an inversion center (i)? (a) neither (b) both (c) only XeF2 (d) only SF2 Why is Symmetry Important? These ideas are an interes0ng and efficient way to describe the shapes of molecules. We also know that the shapes of molecules are dictated by electronic structure and orbital shapes. We can apply these ideas to the symmetry of individual atomic orbitals. What symmetry elements can you find for these atomic orbitals? Why is Symmetry Important? The symmetry of the atomic orbitals is obviously important when these orbitals interact. Interac0ons between orbitals can be “construc0ve”, “destruc0ve” or “zero”. Also note that the labels that are used for orbitals in molecules (e.g., σ, π, π*, etc.) are actually symmetry labels Why is Symmetry Important? The mathema0cal treatment of these symmetry ideas is called Group Theory. For the purposes of this class, we will only have 0me to learn a bit about how to use it, rather than learning all the mathema0cal background. OUR GOALS: ➜  To assign symmetry designa0ons to molecules. ➜  To apply the ideas of symmetry to assist us in describing the bonding interac0ons in molecules. ➜  If there is 0me we may look at some aspects of spectroscopy. ➜  Also to realize that these ideas are common to all areas of chemistry (inorganic, organic, biological and physical) Molecular Symmetry From Symmetry Elements & Opera0ons to Molecular POINT GROUPS. All of the following objects have a C3 axis as their HIGHEST rota0onal axis eclipsed C3 axis, 3 C2 axes, 3σv planes and a σh plane staggered C3 axis, 3 C2 axes, 3σv planes, but no σh plane C3 a...
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