VESPR Model and Geometry. Localized Electron Model Lewis structures are an application of the “Localized Electron Model” L.E.M. says: Electron pairs can.

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Presentation transcript:

VESPR Model and Geometry

Localized Electron Model Lewis structures are an application of the “Localized Electron Model” L.E.M. says: Electron pairs can be thought of as “belonging” to pairs of atoms when bonding Resonance points out a weakness in the Localized Electron Model.

Models Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world. Models can be physical as with this DNA model Models can be mathematical Models can be theoretical or philosophical

Fundamental Properties of Models  A model does not equal reality.  Models are oversimplifications, and are therefore often wrong.  Models become more complicated as they age.  We must understand the underlying assumptions in a model so that we don’t misuse it.

VSEPR – Valence Shell Electron Pair Repulsion X + E Overall Structure Forms 2 LinearAX 2 3 Trigonal PlanarAX 3, AX 2 E 4 TetrahedralAX 4, AX 3 E, AX 2 E 2 5 Trigonal bipyramidalAX 5, AX 4 E, AX 3 E 2, AX 2 E 3 6 OctahedralAX 6, AX 5 E, AX 4 E 2 A = central atom X = atoms bonded to A E = nonbonding electron pairs on A

VSEPR: Linear AX 2 CO 2

VSEPR: Trigonal Planar AX 3 AX 2 E BF 3 SnCl 2

VSEPR: Tetrahedral AX 4 AX 3 E AX 2 E 2 CCl 4 PCl 3 Cl 2 O

VSEPR: Trigonal Bi-pyramidal AX 5 AX 4 E AX 3 E 2 AX 2 E 3 PCl 5 SF 4 ClF 3 I3-I3-I3-I3-

VSEPR: Octahedral AX 6 AX 5 E AX 4 E 2 SF 6 ICl 4 - BrF 5

Actual shape ElectronPairsBonding Pairs Non-Bonding Pairs Shape 220linear 330trigonal planar 321bent 440tetrahedral 431trigonal pyramidal 422bent

Actual Shape ElectronPairsBonding Pairs Non-Bonding Pairs Shape 550trigonal bipyrimidal 541See-saw 532T-shaped 523linear

Actual Shape ElectronPairsBonding Pairs Non-Bonding Pairs Shape 660Octahedral 651Square Pyramidal 642Square Planar 633T-shaped 621linear

Examples SiF 4 SeF 4 KrF 4 BF 3 PF 3 BrF 3

No central atom Can predict the geometry of each angle. build it piece by piece.

How well does it work? Does an outstanding job for such a simple model. Predictions are almost always accurate. Like all simple models, it has exceptions. Doesn’t deal with odd electrons

Polar molecules Must have polar bonds Must not be symmetrical Symmetrical shapes include – Linear – Trigonal planar – Tetrahedral – Trigonal bipyrimidal – Octahedral – Square planar