Molecules of NH3 have a dipole moment but molecules of BH3 don't why?

NH3 has a set of nonbonding electrons, while BH3 does not. The molecule of NH3 shows 3 single bonds between nitrogen and hydrogen, with a nonbonding pair of electrons around nitrogen. BH3, on the other hand, has only three single bonds between hydrogen and boron, with no nonbonding pairs of electrons. The nonbonding pair on NH3 places a force on the bonds between nitrogen and hydrogen, forming a net dipole moment. BH3 doesn't have an extra nonbonding pair, so that force doesn't exist. Hence, NH3 has a dipole moment, and BH3 does not.