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To understand molecular structure and bond angles

Objectives. To understand molecular structure and bond angles To learn to predict molecular geometry from the number of electron pairs To learn to apply the VSEPR model to molecules with double bonds.

june
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To understand molecular structure and bond angles

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  1. Objectives • To understand molecular structure and bond angles • To learn to predict molecular geometry from the number of electron pairs • To learn to apply the VSEPR model to molecules with double bonds

  2. Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. Hemoglobin transports oxygen from the lungs to the rest of the body, such as to the muscles, where it releases the oxygen load.

  3. Draw possible structures that you can think of for the molecules below. Think in three dimensions. A2, AB, AB2, AB3, AB4,AB5,AB6

  4. Structures for some simple molecules

  5. A. Molecular Structure • Three dimensional arrangement of the atoms in a molecule • Water, H2O - bent

  6. A. Molecular Structure • Linear structure – atoms in a line • Carbon dioxide, CO2

  7. A. Molecular Structure • Trigonal planar – atoms in a triangle • Boron Trifluoride, BF3

  8. A. Molecular Structure • Tetrahedral structure • Methane, CH4

  9. 2 balloons 3 balloons 4 balloons 5 balloons 6 balloons B. The VSEPR Model • Valence shell electron pair repulsion (VSEPR) model • Molecular structure is determined by minimizing repulsions between electron pairs • Pairs of electrons in bonds and “lone pairs” influence the molecular structure

  10. B. The VSEPR Model • 180o - linear • Two Pairs of Electrons • BeCl2

  11. B. The VSEPR Model • 120o – trigonal planar • Three Pairs of Electrons • BF3

  12. B. The VSEPR Model • 109.5o – tetrahedral • Four Pairs of Electrons • CH4

  13. B. The VSEPR Model Predicting Molecular Structure using the VSEPR model Draw the Lewis structure Count the pairs of electrons and arrange to minimize repulsions Determine the positions of the atoms Name the molecular structure according to the position of the atoms not the lone electron pairs e.g. NH3 has four pairs of electrons surrounding the N atom which form a tetrahedron. The molecule is named however as a trigonal pyramid

  14. B. The VSEPR Model Predicting molecular shapes H2O molecular shapes molecular shapes 2

  15. C. Molecules with Double Bonds • When using VSEPR model to predict molecular geometry of a molecule a double bond is counted as the same as a single electron pair ethylene H-C-H angle is 120o

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