BCl₃-Trigonal planar, sp²-hybridised, 120^o angle

In CH₄, there is no lone pair of electrons so it is perfectly tetrahedral in shape and has H-C-H bond angle of 109°28′ but in NH₃ there is one lone pair which due to more repulsion with bond pairs of electrons pushes them more closer thus bond angle decreases to 107°. In H₂O, there are two lone pair of electrons which suppress the bond angle more to 104.5°.

According to VSEPR theory, the repulsive forces between lone pair and lone pair are grater than between lone pair and bond pair which are further greater than bond pair and bond pair.