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Molecular Shape

Molecular Shape. The Geometry of molecules. Molecular Geometry. The shape of a molecule is determined by where the nuclei are located. But the nuclei go to certain locations because of the electron pairs. Goal: minimize electron-pair repulsions. Molecular Shape.

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Molecular Shape

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  1. Molecular Shape The Geometry of molecules

  2. Molecular Geometry The shape of a molecule is determined by where the nuclei are located. But the nuclei go to certain locations because of the electron pairs. Goal: minimize electron-pair repulsions.

  3. Molecular Shape Electron pairs repel each other. They want to be as far apart from each other as they can. Nonbonding pairs take up a little more room than bonding pairs They will repel with a greater force.

  4. To determine molecular geometry start with the Lewis e- dot Structure Lewis dot structures are 2-D, but they can help you figure out the 3-D shape. To help us predict the shape of molecules we will use the VSEPR Theory.

  5. VSEPR Theory Valence Shell Electron Pair Repulsion 1) Draw the Lewis structure. 2) Identify the regions of high electron density {Bonding and nonbonding Sites} on the central atom. a) Each single, double, &/or triple bond counts as 1 region of bonded electron density. b) Each nonbonding electron pair counts as 1 region of non-bonded electron density. c) An unpaired electron counts as 1 region of non-bonded electron density. 3) Assign a VSEPR formula according to the # of regions. Resonance structures will fluctuate their regions.

  6. VSEPR Theory The shape is always referenced around the central atom. Determine the formula using A as the central atom X as the bonded atoms or shared pairs around the central atom(A). E as the unshared electron pairs. Example H2O would be AX2E2  A = O ; X2 = H2 ; E2 = 2 unshared pairs of e- .

  7. Most Common VSEPR Shapes Memorize

  8. TWO Share Pairs. LINEAR • 2 bonding regions. • 0 unshared pairs. • Linear. • Bond angle = 180. • Central atom & regions of electron density arranged in a straight line. AX2 : : :ClBeCl: : :

  9. Three Shared pairs Trigonal Planor • Bond angle = 120. AX3 : :F:  B   :F: :F: : : • 3 bonding regions. 0 unshared pairs.

  10. 3 regions of high electron density. • 1 unshared pair. • 2 Shared pairs( one single or double bonds). • NO2- • Lewis Structure: AX2E 1- : : : ONO: : : 3 unequal regions of electron density Since only 2 are shared, the molecule will look bent. What is the bond angle?

  11. Bent slightly < 120° AX2E

  12. H  HCH  H Four shared pairs Tetrahedral Bond angles = 109.5. • 4 shared pairs • 0 unshared pairs • Lewis structure: AX4

  13. : HNH H Trigonal Pyramidal AX3E 107° 3 shared pair 1 unshared pair.  4 regions of electron density would be 109.5 apart. But only 3 end in atoms, not all 4. The molecule will look like a squashed pyramid. Trigonal pyramidal. Bond angles?

  14. 4 regions of electron density. 2 Shared pairs & 2 unshared pairs NH2- with 8 valence electrons: 4 regions of electron density but only 2 end in atoms. Molecule will look bent. AX2E2 Bent 104.5°

  15. 5 regions of electron density

  16. Trigonal Bipyramidal

  17. “See-Saw”

  18. T-shaped

  19. Linear

  20. 6 regions of electron density

  21. Octahedral

  22. Square Pyramid

  23. Square Planar

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