Lecture 24 Final Review

Lecture 24 Final Review - Chem 172 Advanced Inorganic...

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1 Chem 172 Advanced Inorganic Chemistry Lecture 11 Final Review Final Exam Comprehensive Lecture notes Midterm reviews Homework Midterm exams 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. None equivalent positions, outer atoms can lead to complexity in molecular geometry.
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2 Molecular Orbital Theory Molecular Orbital Theory • Molecular orbitals are formed through Linear Combination of Atomic Orbitals (LCAO) • Electrons spread over the entire molecule: collective, roaming • Bonding orbitals are formed from the addition of AOs (constructive interference, lower energy than AOs) • Antibonding orbitals are formed from the subtraction of AOs (destructive interference, higher energy than AOs) • Filling of MO diagram obeys rules of AO diagram n n k c c c ϕ ψ + + + = .... 2 2 1 1 Polyatomic Molecules Molecular orbital theory can be used to describe electronic structure of systems of multiple atoms from 3 to infinite number of atoms (solid), in a way very similar to diatomic molecules. ± MOs are formed by linear combination of AOs of same symmetry. ± The degree of interaction depending on the relative energy match between AOs and distance (interaction between non- nearest neighbor are weaker than nearest neighbors). ± N AOs combine to form N MOs. How to Draw Molecular Orbital Diagram 1. Plot atomic valence orbital energies (or fragment orbitals for more complex molecules) .
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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 24 Final Review - Chem 172 Advanced Inorganic...

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