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CH2Cl2, or dichloromethane has a distorted tetrahedral shape caused by the larger masses of the chlorine atoms compared to the hydrogen atoms. The bond angles between the hydrogen atoms is 112 degrees and 108 degrees between the chlorine atoms.
This is the maximum distance the atoms can be placed away from each other. If you change any of the angles, some of the atoms will be closer together and will experience steric repulsions. By placing the atoms 109.5 degrees apart, you minimize steric repulsions and free energy. ------------------------------------------------------ Edit (AY12345): You know the shape of the molecule. Draw it out. Use a little trigonometry, and the angles can be calculated mathematically.
The molecule of iodine heptafluoride has a bi-pyramidal pentagonal shape. All of the F-I-F angles between two fluorine atoms in axial and equatorial planes are equivalent to 90 degrees. Therefore there is five of them.
120 degrees
Anything with six electron groups, keep in mind an electron group is a bonded atom or an electron pair, is an octahedral. Anything in an octahedral and a lone pair is the square pyramidal geometry. So all angles between the atoms are a little less than 90 degrees and the angle of the electron pair is greater than 90.