VSEPR Theory. Valence Shell Electron Pair Repulsion. VSEPR THEORY: AT THE CONCLUSION OF OUR TIME TOGETHER, YOU SHOULD BE ABLE TO:. Use VSEPR to predict molecular shape Name the 6 basic shapes that have no unshared pairs of electrons Name a few variations off of these basic shapes.
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VSEPR Theory Valence Shell Electron Pair Repulsion
VSEPR THEORY:AT THE CONCLUSION OF OUR TIME TOGETHER, YOU SHOULD BE ABLE TO: Use VSEPR to predict molecular shape Name the 6 basic shapes that have no unshared pairs of electrons Name a few variations off of these basic shapes
Molecular Shapes Lewis structures show which atoms are connected where, and by how many bonds, but they don't properly show 3-D shapes of molecules. To find the actual shape of a molecule, first draw the Lewis structure, and then use VSEPR Theory.
Valence Shell Electron-Pair Repulsion Theory or VSEPR Molecular Shape is determined by the repulsions of electron pairs Electron pairs around the central atom stay as far apart as possible. Electron Pair Geometry - based on number of regions of electron density Consider non-bonding (lone pairs) as well as bonding electrons. Unshared repel the most. Electron pairs in single, double and triple bonds are treated as single electron clouds. Molecular Geometry - based on the electron pair geometry, this is the shape of the molecule
Trigonal Planar • 3 atoms attached to central atom • 0 lone pairs • Bond angle = 120o • Type: AX3 • Ex. : AlF3
Class Shape The Two Molecular Shapes Of The Trigonal Planar Electron-group Arrangement. Examples: H2CO, BCl3, NO3-, CO32-
Effect of Double Bonds 1160 real Factors Affecting Actual Bond Angles Bond angles are consistent with theoretical angles when the atoms attached to the central atom are the same and when all electrons are bonding electrons of the same order. Some exceptions follow: 1200 larger EN 1200 ideal greater electron density
Effect of Nonbonding Pairs Factors Affecting Actual Bond Angles Lone pairs repel bonding pairs more strongly than bonding pairs repel each other 950
Remember the 3 exceptions to the octet rule? • Molecules with atoms near the boundary between metals and nonmetals will tend to have less than an octet on the central atom. (i.e. B, Be, Al, Ga) • Molecules with a central atom with electrons in the 3rd period and beyond will sometimes have more than an octet on the central atom, up to 12, called an extended or expanded octet. • Molecules with an odd number of electrons
