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Feb4-12, 07:31 AM
P: 158
A 120 bond angle is formed when there are just three pair of electron (lone pairs or bond pairs) around an atom. One example being BF3.

-CH3 on the other hand has 4 electron pairs around it, and hence forms a 3D geometric figure, a tetrahedral, to ensure minimum repulsion between electrons. This structure has an angle of 10928' (But can change slightly in case of unlike bonds)