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MOLECULAR���SHAPES���

  Molecules with 2 electron pair groups around the central atom form a linear shape.

2 electron pairs around the central atom

Shape is linear

Linear molecules have polar bonds, but are usually non-polar.

Bond angle is 180

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MOLECULAR���SHAPES���

  Molecules with 3 electron pair groups around the central atom form a trigonal planar shape. Trigonal planar molecules have polar bonds,

but are usually non-polar.

Bond angle is 120 3 electron pairs

around the central atom

Shape is trigonal planar

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MOLECULAR���SHAPES���

  Molecules with 2 bonding pairs and 1 non-bonding pair groups around the central atom form a bent shape.

Bent molecules have polar bonds, and are polar.

Shape is bent

2 bonding pairs around the central atom

1 Non-bonding pair

Bond angle is 120

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MOLECULAR���SHAPES���

  Molecules with 4 electron pairs groups around the central atom form a tetrahedral shape.

Tetrahedral molecules have polar bonds, and are usually non-polar.

4 bonding pairs around the central atom Shape is

tetrahedral Bond angle is 109.5

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MOLECULAR���SHAPES���

  Molecules with 3 bonding pairs and 1 non-bonding pair groups around the central atom form a pyramidal shape.

Pyramidal molecules have polar bonds, and are polar.

Shape is pyramidal

3 bonding pairs around the central atom

1 Non-bonding pair

Bond angle is 109.5

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MOLECULAR���SHAPES���

  Molecules with 2 bonding pairs and 2 non-bonding pair groups around the central atom form a bent shape.

Bent molecules have polar bonds, and are polar.

Shape is bent

2 bonding pairs around the central atom

2 Non-bonding pair

Bond angle is 109.5

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SUMMARY OF���MOLECULAR SHAPES���

Linear

Trigonal planar

Tetrahedral

Bent

Pyramidal

Symmetrical shapes Polar bonds Non-polar molecules

Unsymmetrical shapes

Polar bonds Polar molecules

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ATTRACTIVE FORCES���IN MOLECULES���

  Many differences in the properties of solids and liquids are associated with the attractive forces that keep their molecules together.

  These forces range from very strong to very weak and are responsible for the wide range of properties observed in these substances.

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ATTRACTIVE FORCES���IN MOLECULES���

  Ionic solids have high melting points that are due to the strong nature of the ionic bond and the forces of attraction between the cation and the anion.

Na+

Cl-

ionic bond

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ATTRACTIVE FORCES���IN MOLECULES���

  Covalent molecules also contain attractive forces, but of a weaker nature than the ionic compounds.

  The forces between covalent molecules can be divided into three types:

Dispersion forces

Dipole-dipole attractions

Hydrogen bonds

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DISPERSION���FORCES���

  These forces exist between non-polar molecules, and are the weakest of the 3 types of covalent forces.

  These forces are caused by temporary shifts in distribution of electrons in a non-polar molecule that cause a temporary dipole.

Temporary dipole

F ⎯ F F ⎯ F δ+ δ- δ+ δ-

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DIPOLE-DIPOLE���ATTRACTIONS���

  These forces exist in polar molecules and are moderate strength.

  The negative end of a polar molecule is attracted to the positive end of another such molecule by these forces.

Br⎯ Cl

Br ⎯ Cl

δ+ δ- δ+ δ-

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HYDROGEN���BONDS���

  These are the strongest of the 3 types of forces and are formed between molecules that have a hydrogen attached to the very electronegative elements (F, O and N).

H⎯ F H ⎯ F δ+ δ- δ+ δ-

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HYDROGEN BONDING���IN WATER���

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THE END