151F09_W10_LV_2 - UA GenChem General Chemistry General...

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Unformatted text preview: UA GenChem General Chemistry General Chemistry CHEM 151 CHEM 151 Week 10 UA GenChem Molecular Geometry Molecular Geometry VSEPR THEORY V alence S hell E lectron P air R epulsion Theory The most important factor in determining geometry is the relative repulsion between electron groups around the central atom Molecules adopt the shape Molecules adopt the shape that minimizes the electron that minimizes the electron repulsions repulsions UA GenChem We will roughly approximate a single bond, double bond, triple bond or unshared pair as one Electron Group or a region of electron density. : : .. .. .. .. O O O Cl F F : : .. .. .. .. Xe F F F F F F Br F F F . . . . (Unshared pairs on F not shown) Electron Groups Electron Groups The central atom in each structure has ______ bonds and _______ electron groups ? .. .. .. O C O .. 4, 2 3, 3 2, 4 3, 5 6, 6 UA GenChem How do you find the electron geometry of any molecule ? a) Build the best Lewis structure of the molecule b) Count the number of electron groups around the central atom. c) Identify the shape in which the repulsion of groups would be minimal. Electron Group Geometry Electron Group Geometry UA GenChem Molecular Geometry Molecular Geometry The distribution of electrons in a molecule determines and is determined by how the atoms arrange in space. UA GenChem TWO Groups around central atom H C N : .. .. .. O C O .. .. .. .. Be F F : : .. Like the balloons shown here, repulsion between two groups is minimized when they are arranged in a straight line ( linear ). Electron Geometry LINEAR UA GenChem . . . . N H N H THREE Groups around central atom Electron Geometry TRIGONAL PLANAR C H H O : : Minimal repulsion from three groups, is achieved when they are arranged in a flat triangle . B F F F : : : : .. .. .. .. .. UA GenChem 120 planar trigonal F F B F 3 180 linear 2 Geometry Example No. of e- Groups Around Central Atom FBeF Summary (including bond angles): UA GenChem FOUR Groups around central atom .....
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151F09_W10_LV_2 - UA GenChem General Chemistry General...

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