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Molecular Geometries and Bonding Theories

Molecular Geometries and Bonding Theories. Learning Objectives. be able to draw ‘dots and crosses’ diagrams for covalent compounds be able to use valence shell electron pair repulsion theory (VSEPR) to predict the shapes of molecules be able to draw representations of molecular shapes.

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Molecular Geometries and Bonding Theories

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  1. Molecular Geometriesand Bonding Theories

  2. Learning Objectives be able to draw ‘dots and crosses’ diagrams for covalent compounds be able to use valence shell electron pair repulsion theory (VSEPR) to predict the shapes of molecules be able to draw representations of molecular shapes

  3. We’ve learned to draw Lewis structures (dots and crosses) But: Lewis structures are two dimensional and molecules are 3 dimensional objects. The 3D structure is absolutely critical for understanding molecules. Molecular Shapes

  4. What Determines the Shape of a Molecule? • atoms and lone pairs take up space and prefer to be as far from each other as possible • shape can be predicted from simple geometry lone pair bonds

  5. Valence Shell Electron Pair Repulsion Theory (VSEPR) “The best arrangement of a given number of things is the one that minimizes the repulsions among them.”

  6. These are the geometries for two through six things around a central atom. You must learn these! number of thingsarrangementgeometry bond angles Geometries

  7. Geometries vs. shape Within each geometry, there might be more than one shape.

  8. In this geometry, there is only one molecular geometry: linear. NOTE: If there are only two atoms in the molecule, the molecule will be linear no matter what the geometry is. Linear geometrytwo things things geometry atoms lone pairs shape example

  9. There are two molecular geometries: Trigonal planar, if there are no lone pairs Bent, if there is a lone pair. Trigonal Planar geometry3 things things geometry atoms lone pairs shape example

  10. Lone pairs and Bond Angle • Lone pairs are physically larger than atoms. • Therefore, their repulsions are greater; this tends to decrease bond angles in a molecule.

  11. There are three molecular geometries: Tetrahedral, if no lone pairs Trigonal pyramidal if one is a lone pair Bent if there are two lone pairs Tetrahedral geometry 4 things Things geometry atoms lone pairs shape example

  12. There are two distinct positions in this geometry: Axial Equatorial Trigonal Bipyramidal geometry5 things

  13. Lower-energy conformations result from having lone pairs in equatorial, rather than axial, positions in this geometry. Trigonal Bipyramidal geometry

  14. Trigonal Bipyramidal geometry Things geometry atoms lone pairs shape example • There are four distinct molecular geometries in this domain: • Trigonal bipyramidal • Seesaw • T-shaped • Linear

  15. All positions are equivalent in the octahedral domain. There are three molecular geometries: Octahedral geometry 6 things Things geometry atoms lone shape example pairs

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