NBr3, or Bromine Trinitride, is considered to be a polar molecule. This polarity arises primarily from its molecular geometry and the electronegativity of its constituent atoms.
The molecule features a central nitrogen atom bonded to three bromine atoms. The nitrogen-bromine bonds are polar due to the difference in electronegativity between nitrogen (3.04) and bromine (2.96), with nitrogen being slightly more electronegative. However, it’s the molecular shape that ultimately determines the overall polarity.
NBr3 adopts a trigonal pyramidal shape due to the presence of a lone pair of electrons on the nitrogen atom. This leads to an asymmetrical distribution of electron density. In molecules, when there is an uneven distribution of charge, the molecule exhibits dipole moments. The vectors representing these dipole moments do not cancel out in NBr3, resulting in a net dipole moment.
In contrast, if a molecule were symmetrical, such as boron trifluoride (BF3), the individual bond polarities would cancel each other out, leading to a nonpolar molecule. However, in NBr3, the asymmetry and the presence of the lone pair contribute to its polar nature.
In summary, due to its shape and the difference in electronegativities of nitrogen and bromine, NBr3 is classified as a polar molecule.