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X. VSEPR Theory –

X. VSEPR Theory – . V alence S hell E lectron P air R epulsion theory . [Remember: Like charges repel!] A. A theory to predict the 3-dimensional geometry, ie . the“ shape ” of a molecule.

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X. VSEPR Theory –

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  1. X. VSEPR Theory – • Valence Shell Electron Pair Repulsion theory. [Remember: Like charges repel!] • A. A theory to predict the 3-dimensional geometry, ie. the“shape” of a molecule

  2. 1. The theory is based on “electrostatic repulsion”: Molecules will adjust their shape to keep the negatively-charged pairs of valence electrons as far apart as possible from each other. • B. When NOT to use VSEPR theory: When there are only 2 atoms in a molecule. These molecule’s shapes are calledlinear – it doesn’t matter if there are single bonds, double bonds, triple bonds, or unshared electron pairs.

  3. C. Using VSEPR theory: • 1. Draw the Lewis dot structure for the molecule. • 2. Identify its central atom. • 3. Identify the sets of valence electrons as one of two possibilities: • A. Those connecting two atoms. • B. Those that do not connect two atoms. These are called “unshared pairs”.

  4. 4. The unshared pairs found on a central atom strongly repel each other; and molecules that would otherwise be linear, will be forced into a bent (or angular) shape. • 5. Unshared pairs also cause a molecule that would be shaped like a flat triangle (trigonal planar), to be forced into a not flat ( trigonal pyramidal) shape.

  5. 6.Count the number of connections separately from the number of unshared pairs. • 1 single bond counts as 1 connection. • 1 double bond counts as 1 connection. • 1 triple bond counts as 1 connection. • Each unshared set of 2 dots counts as 1 un-shared pair.

  6. D Predicting Shapes Using VSEPR Table • Read horizontally across the table. # of total atoms 3 4 5 3 4

  7. Linear diatomic E. Shap e s: Trigonal Planar Bent Linear diatomic Linear triatomic Tetrahedral Pyramidal Shapes: , Trigonal planar bent Linear triatomic Trigonal pyramidal tetrahedral

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