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Molecular Geometry

CP Chemistry 10-11-2010. Molecular Geometry. Lewis Structures. PROS Suggests how many valence electrons we’re dealing with EASY to make. CONS Exceptions to the Octet Rule Hydrogen (happy with 2 or 0) Hypervalent (more than 8) Hypovalent (less than 8)

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Molecular Geometry

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  1. CP Chemistry 10-11-2010 Molecular Geometry

  2. Lewis Structures PROS • Suggests how many valence electrons we’re dealing with • EASY to make CONS • Exceptions to the Octet Rule • Hydrogen (happy with 2 or 0) • Hypervalent (more than 8) • Hypovalent (less than 8) • Lewis structures do not indicate the three dimensional shape of a molecule.

  3. Why Care About Shape?…

  4. Why Care About Shape?...

  5. So How Do We Show Shape? VSEPR Theory V Valence S Shell E Electron P Pair R Repulsion VSEPR, VSEPR…

  6. Basic Assumptions of VSEPR Theory • Opposites Attract!...And likes repel!

  7. Basic Assumptions of VSEPR Theory • What would two particles that have the same charge do when they came close to one another? • Think of electrons as being extremely antisocial • The goal is simple – GET AS FAR AWAY FROM EACH OTHER AS POSSIBLE… • It is the desire to get away from one another that gives each molecule its unique shape

  8. Try this one to get us started… • Carbon dioxide (CO2) • Start with Lewis structure • Show how it bonds • Think about the shape • Linear Shape (180 degrees)

  9. Try this one to get us started… • BH3 • Start with Lewis structure • Show how it bonds • Think about the shape • Trigonal Planar (120 degrees)

  10. Try this one to get us started… • CH4 • Start with Lewis structure • Show how it bonds • Think about the shape • Tetrahedral (90 degree angle?)

  11. Try this one to get us started… • Water • Start with Lewis structure • Show how it bonds • Think about the shape • Bent (180 degrees?)

  12. Why not 180 Degrees?

  13. O H H

  14. Try this one to get us started… • Phosphorous pentachloride (PCl5) • Start with Lewis structure • Show how it bonds • Think about the shape • Trigonalbipyramidal(120, 90 degrees)

  15. A More Systematic Approach… • The central atom is referred to as A • The attached atoms are referred to as B • Any lone PAIRS of electrons on the central atom are referred to asE 3) Any lone pair electrons are designated with an E.

  16. Predict the shapes of the following… • BCl3 • CCl2 • SiO2 • BeCl2 • CCl4 • PBr5

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