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Recap VSEPR Theory

Recap VSEPR Theory. Draw Lewis Structure. Count number of electron pairs. Determine the arrangement of electron pairs. Use atom positions to name molecular geometry. Recap . Three areas of electrons : Trigonal Planar

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Recap VSEPR Theory

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  1. Recap VSEPR Theory • Draw Lewis Structure. • Count number of electron pairs. • Determine the arrangement of electron pairs. • Use atom positions to name molecular geometry.

  2. Recap Three areas of electrons: Trigonal Planar • Remove one arm from the electron pair arrangement for each lone pair present. SO3 SO2 Figure 10.4 Silberberg

  3. Recap Four areas of electrons: Tetrahedral Figure 10.5 Silberberg CH4 NH3 H2O

  4. Electron Pair Arrangements • Five electron pairs: • Atoms at the corners of a trigonal bipyramid. • Some electron pairs separated by 120 degrees, other by 90 degrees. • Called trigonal bipyramidal. Figure 10.2 Silberberg

  5. Electron Pair Arrangements • Six electron pairs: • Atoms at the corners of an octahedron. • 90 degrees between electron pairs. • Called octahedral. Figure 10.2 Silberberg

  6. Axial Equitorial Where do lone pairs go? • Five electron pairs: • If one lone pair present is it in an axial or equatorial position? • Repulsion: lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.

  7. Molecular Geometry Structures derived from a trigonal bipyramid Figure 10.7 Silberberg

  8. Molecular Geometry Structures derived from an octahedron All positions are identical Figure 10.8 Silberberg

  9. Summary of Molecular Geometry Total number of electron pairs

  10. Molecular Geometry and Polarity BF3 ClF3 Non-Polar Polar

  11. Molecular Geometry and Polarity SiF4 SF4 Non-Polar Polar

  12. Learning Outcomes: By the end of this lecture, you should: be able predict the molecular geometry of molecules and ions containing a central atom be able to name the geometry of a given species understand the positioning of lone pairs to minimise repulsion be able to predict the presence of a permanent dipole moment be able to complete the worksheet (if you haven’t already done so…)

  13. Questions to complete for next lecture: • Give the geometry of the following polyatomic ions and give approximate bond angles. • AsF6- • PBr4- • SF5- • SO42- • ICl2- • N3- • A binary compound contains two different elements. What molecular geometries would result in binary compounds that are polar? • Whatmolecular geometries would result in binary compounds that are non-polar?

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