L18 - VSEPR Valence Shell Electron Pair Repulsion Theory An electron group can be a nonbonding electron pair a single bond or a multiple bond

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    VSEPR - Valence Shell Electron Pair Repulsion Theory Each group of valence electrons around a  central atom is located as far away as possible  from the others in order to  minimize  repulsions.  Thus, the space each group occupies is  maximized . The result is five electron-group arrangements of minimum energy seen in a large majority of molecules and polyatomic ions. Note: molecular shapes are defined by the relative positions of the nuclei. Because valence electrons can be bonding or nonbonding, the same electron-group  arrangement can give rise to different molecular shapes; shape type/class: AX m E n . An   electron   group   can be a non-bonding electron pair, a single bond, or a  multiple bond  around the central atom trigonal planar C O H H double bond single bonds
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    Electron-group repulsions and the five basic molecular shapes. linear trigonal planar tetrahedral trigonal bipyramidal octahedral
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    Factors Affecting  Actual Bond Angles Bond angles are consistent with theoretical (ideal) angles when the atoms  attached to the central atom are the same and when all electrons are bonding  electrons of the same order. Bond angles differ from ideal angles if some  electrons are non-bonding or if bonds are of different order. C O H H ideal 120 0 120 0 larger EN greater  electron  density C O H H 122 0 116 0 real Lone pairs repel bonding pairs more  strongly than bonding pairs repel each  other. Sn Cl Cl 95 0 Effect of Double Bonds Effect of Nonbonding(Lone) Pairs
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    The steps in determining a molecular shape. Molecular  formula Lewis  structure Electron-group  arrangement Bond angles Molecular  shape  (AX m E n ) Count  all  e -  groups around central  atom (A) Note lone pairs and double  bonds Step 1 Step 2 Step 3 Step 4 See Figure  10.1 Count bonding and  nonbonding e -  groups  separately.
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    Using VSEPR theory to predict the molecular shape: 
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This note was uploaded on 04/20/2008 for the course CHEM 111 taught by Professor Grzegorz during the Spring '08 term at Colorado State.

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L18 - VSEPR Valence Shell Electron Pair Repulsion Theory An electron group can be a nonbonding electron pair a single bond or a multiple bond

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