Why is NH4 a polar molecule but BF3 a non polar? (DIPOLE MOMENT)
The Correct Answer and Explanation is:
The polarity of a molecule depends on its molecular geometry and the distribution of its electron density. This results in a net dipole moment, which is a measure of the overall polarity of the molecule.
NH4+ (Ammonium ion) is a polar molecule despite being a positively charged ion. This is because of its tetrahedral geometry, where the four hydrogen atoms are symmetrically arranged around the nitrogen atom. In this configuration, the bonds between nitrogen and hydrogen are polar due to the difference in electronegativity between nitrogen and hydrogen. Nitrogen is more electronegative, so it pulls electron density towards itself. However, since the geometry is perfectly symmetrical, the individual bond dipoles cancel each other out, resulting in a net dipole moment of zero. Despite the lack of a net dipole moment, the molecule remains polar due to the unequal distribution of charge across the ion. The positive charge is concentrated on the nitrogen atom, and it has an overall dipole moment due to its structure.
BF3 (Boron trifluoride), on the other hand, is a nonpolar molecule. BF3 adopts a trigonal planar geometry, with the three fluorine atoms symmetrically arranged around the boron atom. Although each B-F bond is polar because fluorine is much more electronegative than boron, the symmetry of the molecule means that the individual bond dipoles cancel each other out. The electron density is evenly distributed around the boron atom, and there is no net dipole moment. As a result, despite the polar B-F bonds, BF3 does not have an overall dipole moment and is considered nonpolar.
In summary, NH4+ is polar because of its asymmetric electron density distribution and positive charge, while BF3 is nonpolar due to its symmetrical geometry, which causes the individual bond dipoles to cancel out.
