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Chapter 10

Chapter 10. CHM 108 Suroviec Spring 2014. I. VSEPR Theory. A simple model that we can use to look at molecular shapes is the VSEPR (valence shell electron pair repulsion) theory Theory is based on the idea that electron groups repel one another through columbic forces.

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Chapter 10

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  1. Chapter 10 CHM 108 Suroviec Spring 2014

  2. I. VSEPR Theory • A simple model that we can use to look at molecular shapes is the VSEPR (valence shell electron pair repulsion) theory • Theory is based on the idea that electron groups repel one another through columbic forces

  3. A. 2 electron groups - Linear • BeCl2 • CO2

  4. B. 3 electron groups – Trigonal Planar • BF3 • CH2O

  5. C. 4 electron groups - tetrahedral • CH4

  6. D. 5 and 6 electron groups • Trigonal Bipyramidal • PCl5 • Octahedral • SF6

  7. 10_T0102.JPG

  8. II. VSEPR Theory and Lone Pairs • We just looked at molecules with all atoms bonded, what if there were lone pairs involved?

  9. A. Four electron groups with lone pairs • NH3 • H2O

  10. B. 5 electron groups with lone pairs • SF4 • BrF3

  11. C. 6 electron groups with lone pair • BrF5 • XeF4

  12. Summary • Geometry of a molecule is determine by number of electron groups on central atom • Number of electron groups depends on correct Lewis structure • Each of the following counts as a single electron group • Geometry of electron groups is determined by minimizing their repulsion

  13. II. Molecular Shape and Polarity • In Lewis structures covalent bonds look like the electrons are shared equally, but that is not always true Ex. HF and H2

  14. II. Molecular Shape and Polarity • In a polyatomic molecule having a polar bond may or may not result in a polar molecule • Ex. CO2 vs. H2O

  15. II. Molecular Shape and Polarity B. Summary 1. Draw Lewis Structure 2. Determine the VSEPR stucture 2. Determine if there are any polar bonds 3. Determine if polar bonds add together to make a net dipole moment Ex. CH4, NH3, BF3, CS2

  16. C. Polar, covalent and ionic • Polar: unsymmetrical distribution of electrons • Nonpolar: symmetrical distribution of electrons • Ionic: complete transfer of electrons

  17. Increasing difference in electronegativity C. Classification of bonds by difference in electronegativity Difference Bond Type 0 Covalent  2 Ionic 0 < and <2 Polar Covalent

  18. Classify the following bonds as ionic, polar covalent,or covalent: The bond in CsCl; the bond in H2S; and the NN bond in H2NNH2. Cs = 0.7 Cl = 3.0 H = 2.1 S = 2.5 N = 3.0 N = 3.0

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