Lecture 11 Review - Lewis structure: Chem 172 Advanced...

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1 Chem 172 Advanced Inorganic Chemistry Lecture 11 Review of Simiple Bonding and Molecular Orbtial Theory Lewis structure: Octet Rule: for many molecules, each atom shares electrons with neighboring atoms to achieve a total of eight valence electrons (an ‘Octet’) ( except H ). (1) decide total number of valence electrons provided by all atoms (2) write chemical symbols of the atoms in the arrangement with bonded atoms next to each other. (3) distribute electron pairs so that there is one pair between each pair of bonded atoms, with the extras for lone pairs or multiple bond. within octet rule, in general: # of bonds = (# of atoms x 8 - # of valence electrons)/2 ( if H, x2 ) Valence Shell Electron-Pair Repulsion Theory (VSEPR) Allows the prediction of molecular geometry (1) Count up the number of steric contribution around the central atom. Steric number (SN) = # of attached atom + # of lone pairs (2) Assume that electron pairs around central atom repel each other, the most stable geometry requires to position the valence electrons pairs as far as possible to minimize electron-electron repulsion. (3) In general, for any steric point that may cause larger electron density near the central atom ( lone pairs, multiple bonds, electron given outer atoms (less electronegativity ), will require more space to minimize electron-electron repulsion. The most stable geometry is obtained by maximizing the distance between SN points on the surface of a sphere. Molecules with same outer atoms adopts regular geometries to minimize the electron-electron repulsion.
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This note was uploaded on 06/27/2010 for the course CHEMISTRY Chem 172 taught by Professor Duan,x. during the Spring '10 term at UCLA.

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Lecture 11 Review - Lewis structure: Chem 172 Advanced...

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