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Molecular Structure Prediction: VSEPR Model & Geometry Examples

Learn how to predict molecular structures using the VSEPR model, from linear and tetrahedral to trigonal planar and pyramidal arrangements. Steps include drawing Lewis structures, minimizing electron pair repulsions, and determining atom positions. Understand how double bonds are considered in molecular geometry. Examples provided for CO2, H2O, SO3, BF3, NH3, and CH4.

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Molecular Structure Prediction: VSEPR Model & Geometry Examples

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  1. Notes 12.4 Chemistry • Molecular Structure • Linear, bent • Trigonal planar, trigonal pyramidal • tetrahedral

  2. The VSEPR Model • The structure around a given atom is determined by minimizing repulsions between electron pairs. • Whenever two pairs of electrons are present around an atom, they should always be placed at an angle of 180 degrees to each other to give a linear arrangement • Whenever three pairs of electrons are present around an atom, they should always be placed at the corners of a triangle (in a plane at an angle of 120 degrees to each other). • Whenever four pairs of electrons are present around an atom, they should always be placed at the corners of a tetrahedron (the tetrahedral arrangement).

  3. Steps for Predicting Molecular Structure Using the VSEPR Model • Draw the Lewis Structure for the molecule • count the electron pairs and arrange them in a way that minimizes repulsions ( that is, put the pairs as far apart as possible). • Determine the positions of the atoms from the way the electron pairs are shared. • Determine the name of the molecular structure from the positions of the atoms. • Molecules with Double Bonds • When using the VSEPR model to predict the molecular geometry of a molecule, a double bond is counted the same as a single electron pair.

  4. Examples Draw VSEPR for the following examples: CO2 H2O SO3 (BF3) NH3 CH4

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