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Download Lesson 07 - VSEPR Theory And Molecular Shapes
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VSEPR Theory and Molecular Shapes A molecule’s shape is determined by its bond angles Carbon dioxide is linear, whereas water is bent VSEPR = valence shell electron pair repulsion Any bond (single, double or triple) functions as an electron domain Nonbonding electron pairs also function as an electron domain The electron domains will arrange themselves about the central atom so that the repulsions are minimized The shapes of different molecules or ions depend on the number of electron domains surrounding the central atom Each class of shapes in VSEPR can be expressed by AXmEn A : the central atom X : atoms bonded to the central atom E : lone pairs on the central atom Linear Molecules A central atom with two electron domains forms a linear shape to place the domains as far apart as possible The bond angle in a linear molecule is 180o AX2 molecules have a linear shape Any diatomic molecule (AX, AXE, AXE2, AXE3) will always be linear Trigonal Planar Molecules A central atom with three electron domains has a trigonal planar electron domain geometry If all 3 domains are bonding domains (AX3) , the bond angle will be 120o Methanal (CH2O) is trigonal planar When 1 of the 3 electron domains is a lone pair, the designation is AX2E Molecules with the AX2E symbol have a bent molecular geometry Sulfur dioxide (SO2) is a bent molecule Tetrahedral Molecules A central atom with four electron domains has a tetrahedral electron domain geometry If all 4 domains are bonding domains (AX4), the bond angle will be 109.5o When 1 of the 4 electron domains is a lone pair, the designation is AX3E Molecules with the AX3E symbol have a trigonal pyramidal molecular geometry Ammonia (NH3) is trigonal pyramidal When 2 of the 4 electron domains are lone pairs, the designation is AX2E2 Molecules with the AX2E2 symbol have a bent molecular geometry Water (H2O) is bent Predict the electron-domain geometry and the molecular geometry for the following molecules: (a) O3 (b) SnCl3− (c) SeCl2 (d) CO32−
