1 / 17

Molecular Geometry

Molecular Geometry. Watson and Crick with their famous 3-D model of DNA How did they know? Shape of molecules important as influences their physical and chemical behavior. “The shape of things to come”. What Determines the 3-D Shape of a Molecule?.

aideen
Télécharger la présentation

Molecular Geometry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Molecular Geometry • Watson and Crick with • their famous 3-D • model of DNA • How did they know? • Shape of molecules important as influences their physical and chemical behavior “The shape of things to come”

  2. What Determines the 3-D Shape of a Molecule? • Need to understand electrostatic repulsion • Need to draw Lewis structures • Need to differentiate between lone pair electrons and bonding pair electrons around the central atom in a molecule • Need to apply a theory based on all of the above

  3. Lone pair e- Lewis Structure Bonding pair e- • Electron pairs are also called domains • Electron domains try to stay out of each • others way (to minimize repulsion)

  4. Valence Shell Electron Pair Repulsion Theory • VSEPR, for short • Proposed by English chemist Ron Gillespie in the 1950s • Based on Lewis structures of molecules andelectron repulsion

  5. VSEPR Theory Rules • In a molecule, electron domains (pairs) will orient themselves around the central atom in an arrangement that minimizes the repulsions among them. • The shapes of different molecules or ions depend on the number of electron domains surrounding the central atom. • Lone pair electrons count as 1 electron domain; single, double or triple bonding pair electrons count as 1 electron domain.

  6. Applying VSEPR Rules LiH • Draw Lewis Structure Li : H 2. Count # of lone pair and bonding pair e- around central atom. 3. 0 l.p. e-, 1 b.p. e- = linear geometry Li-H Generalization – molecules having 0 lone pair e- and 1 bonding pair e- around the central atom will have a linear shape

  7. Other Linear Molecules Bonding pair e- CO2 Lewis Structure • 2 bonding pair e-, 0 lone pair e- • 2 b.p. e- get as far apart as possible (180°) • Shape is Linear Central atom

  8. Other Linear Molecules BeH2 • Lewis Structure • 2 bonding pair e-, 0 lone pair e- • Shape = Linear HF • Lewis structure Linear • 1 b.p. e-, 3 l.p. e-

  9. BH3 Lewis Structure • 3 bonding pair e-, 0 lone pair e- • Minimization of repulsion dictates the 3 bonding pair e- orient themselves toward the corners of a triangle Triangular or Trigonal Planar

  10. CH4 Lewis Structure • 4 bonding pair e-, 0 lone pair • Minimization of repulsion = orientation of b.p. e- towards the corner of a tetrahedron • Tetrahedral

  11. NH3 Lewis Structure • 3 bonding pair e- • 1 lone pair e- Minimization of repulsion = pyramidal shape

  12. H2O Lewis Structure • 2 lone pair e- • 2 bonding pair e- Minimization of repulsion = Bent or V shape

  13. Polarity of Molecules • Polar molecules must meet 2 criteria • Bonds in molecule must be polar covalent • Shape of molecule must be asymmetrical • Examples NH3, H2O

  14. Polarity of Molecules

More Related