Shapes of Molecules

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Electron Repulsion Theory

- The electron pairs surrounding a central atom determine the shape of the molecule or ion

- The electron pairs repel one another so that they are arranged as far apart as possible

- The arrangement of electron pairs minimises repulsion and therefore holds the bonded atoms in a definite shape

- The greater the number of electron pairs, the smaller the bond angle

- Different number of electron pairs result in different shapes

A lone pair of electrons is slightly closer to the central atom, and occupies more space than a bonded pair. This results in a lone pair repelling more strongly than a bonding pair

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Methane

(http://people.uwplatt.edu/~sundin/images/vsprch4.gif)

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Ammonia

(http://itech.dickinson.edu/chemistry/wp-content/uploads/2008/04/molecular-structure-of-ammonia.png)

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Water

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Sulfur Hexafluoride

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Boron Trifluoride

(http://people.uwplatt.edu/~sundin/images/vsprbf3.gif)

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Beryllium Chloride

(http://www.4college.co.uk/as/el/SHAPE5.gif)

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Ammonium

(http://www.chemguide.co.uk/atoms/bonding/shapenh4.GIF)

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Carbonate Ion

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