Why is NH3 a polar molecule and BF3 a nonpolar molecule?
Ammonia
Since the molecular geometry of NH3 is trigonal pyramidal, the vector sum of the three H-N bond dipole moments, uHN = 1.33 D, is 1.47 D and the NH3 molecule is polar .
Boron Trifluoride
In a trigonal planar molecule such as BF3 the vector sum of the three FB bond dipole moments, uFB = 2.17 D, is 0.0 D and the molecule is nonpolar.
