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Molecular Geometry

Molecular Geometry. VSEPR - Valence Shell Electron Pair Repulsion Theory. In small molecules, electrons and bonds are arranged as far apart as possible. Molecular Geometry. This allows for atoms to have 3-D shapes different from their shapes in 2-D (paper). Molecular Geometry.

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Molecular Geometry

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  1. Molecular Geometry • VSEPR - Valence Shell Electron Pair Repulsion Theory. • In small molecules, electrons and bonds are arranged as far apart as possible.

  2. Molecular Geometry • This allows for atoms to have 3-D shapes different from their shapes in 2-D (paper).

  3. Molecular Geometry • Linear – the bonds form a straight line. • Example CO2 • Bond Angle 180⁰ [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH10/FG10_02-02d.JPG]

  4. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

  5. Molecular Geometry • Trigonal Planar– The central atom has only 3 bonds. • Example: CH2O (Formaldehyde) • Bond angle 120⁰ [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_10/FG10_00-66c.JPG]

  6. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

  7. Molecular Geometry • Tetrahedral –The central atom has only 4 bonds • Example: CH4 (methane) • Bond Angle 109.5⁰ [http://wps.prenhall.com/wps/media/objects/476/488316/Instructor_Resources/Chapter_10/FG10_00-69d.JPG]

  8. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

  9. Molecular Geometry • Trigonal Pyramidal –Central atom has 3 bonds and one lone pair of electrons that “pushes” the bonds away. • Example: NH3 (ammonia)

  10. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

  11. Molecular Geometry • Bent – Here there are two bonds and two pairs of electrons on the central atom. • Example: H2O (water) [http://www.elmhurst.edu/~chm/vchembook/images/206water.gif]

  12. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

  13. [http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG][http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]

  14. Polarity • When 2 atoms in a bond have different electronegativity values, electrons can be “pulled” more toward one side of the bond. • A bond where this occurs is called a dipole.

  15. [http://www.cybered.net/library/Teaching_Resources/Chemistry/Bonding_II/Image_Gallery/Bonding2--PolarBond.jpg][http://www.cybered.net/library/Teaching_Resources/Chemistry/Bonding_II/Image_Gallery/Bonding2--PolarBond.jpg]

  16. [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11.JPG][http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11.JPG]

  17. Polarity • Showing Polarity • “Minus” sign above the high electronegative atom. • “Plus” sign over the other atom. • Draw arrow from plus to minus. [http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11-02.JPG]

  18. Compound Polarity • Draw a correct 2-D compound with arrows along each bond. • Example: CH4 H H C H H

  19. Compound Polarity • Then, check to see if any of the arrows cancel out. • To do this think “tug of war” H H C H H

  20. Compound Polarity • If all arrows cancel out, the molecule is non-polar or covalent. • If the arrows do not cancel out, the molecule is polar or polar-covalent.

  21. Compound Polarity • Remember: 3D shape determines 2D drawing. • Example: H2O H O H H O H

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