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V alence S hell E lectron P air R epulsion Theory

V alence S hell E lectron P air R epulsion Theory. Planar triangular. Tetrahedral. Trigonal bipyramidal. Octahedral. VSEPR Theory. Based on Lewis structures we can know the shape or “geometry” of molecules VSEPR (pronounced “vesper”) stands for Valence Shell Electron Pair Repulsion

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V alence S hell E lectron P air R epulsion Theory

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  1. ValenceShellElectronPairRepulsionTheory Planar triangular Tetrahedral Trigonal bipyramidal Octahedral

  2. VSEPR Theory • Based on Lewis structures we can know the shape or “geometry” of molecules • VSEPR (pronounced “vesper”) stands for Valence Shell Electron Pair Repulsion • VSEPR, as the name suggests, predicts geometry based on the repulsion of electron pairs (in bonds or by themselves) • Electrons around the central nucleus repel each other. Thus, resulting structures have atoms maximally spread out

  3. VSEPR overview • 2 Principles of the Theory • Electron pairs repel each other • 2 kinds of pairs • Bonded pairs (shared between atoms) • Lone pairs (NOT shared) • Molecules are represented by AXY, where A is the central atom and Y is the # of peripheral atoms • AX2 = linear • AX3 = planar triangular • AX4 = tetrahedral (tetra = 4 faces) • AX5 = trigonal bipyramidal (2 pyramids) • AX6 = octahedral (octa = 8 faces)

  4. Planar triangular Tetrahedral Trigonal bipyramidal Octahedral

  5. H H H N H H C H H C H H N H H H H H Lone pairs • Thus far we have considered (built) only structures where there are no free electrons around the central atom Vs. or or • These electrons that are not involved in bonds are called “lone pairs” • Essentially, they have the same influence on molecular structure as electron pairs in bonds • The result is some weird shapes and names…

  6. Variations on Tetrahedral Molecule • The tetrahedral molecule is AX4 • Lone pairs can be indicated with AXYEZ, where Z is the number of lone pairs • By replacing 1 bond with a lone pair the tetrahedral shape becomes “trigonal pyramidal” • AX3E • By replacing two bonds with lone pairs we get a “bent” (non-linear) shape (AX2E2 ) (Fig. 3.26, pg. 87)

  7. Variations on Trigonal Bipyramidal • AX5 is trigonal bipyramidal • AX4E is unsymmetrical tetrahedron • AX2E3 is linear See Fig. 3.37 on pg. 91 • AX3E2 is T-shaped

  8. Variations on Octahedral Shape • AX6 is octahedral • AX5E is square pyramidal • AX4E2 is square planar

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