Why do bond angles in CH4, NH3, and H20 differ?
##CH_4## has 4 sigma bonds and no lone pairs or pi bond. Thus its hybridization is sp3 and its bond angle is 109.5 degrees.
##NH_3## has 3 sigma bonds and one lone pair as nitrogen has 5 valence electrons in it. Its hybridization is also sp3 but due to a lone pair its strcture will be trigonal pyramidal and bond angle decreases to 107 degrees.
##H_2O## has 2 sigma bonds and two lone pairs as Oxygen has 6 valence electrons. Its hybridization is also sp3 but its structure is V shape or bent due to two lone pairs and bond angle is reduced to 104 degrees.
LONE PAIR tends to decrease the bond angle and also changes the shape of compound.