Which of the following molecules is non-polar?
BCl3
H2O
NCl3
PCl3
all are polar
The correct answer and explanation is:
The correct answer is BCl3.
Explanation:
A molecule’s polarity is determined by the arrangement of its atoms and the distribution of electrons within the molecule. To determine if a molecule is polar or non-polar, the molecular geometry and the difference in electronegativity between the atoms need to be considered.
- BCl3 (Boron Trichloride):
BCl3 has a trigonal planar geometry with boron at the center and chlorine atoms at the corners. The three B-Cl bonds are arranged symmetrically, and because the chlorine atoms are all the same, the bond dipoles cancel each other out. The electronegativity of boron and chlorine is different, but the molecule is non-polar due to its symmetrical structure. There are no net dipoles, which makes BCl3 non-polar. - H2O (Water):
H2O has a bent shape due to the lone pairs of electrons on the oxygen atom. Oxygen is more electronegative than hydrogen, creating polar bonds between oxygen and hydrogen. The bent structure means the dipoles from the O-H bonds do not cancel out, making water a polar molecule. - NCl3 (Nitrogen Trichloride):
NCl3 has a trigonal pyramidal shape with nitrogen at the apex and chlorine atoms at the corners. Due to the lone pair on nitrogen, the structure is not symmetrical, causing the dipoles from the N-Cl bonds to add up and give the molecule an overall dipole moment. Hence, NCl3 is polar. - PCl3 (Phosphorus Trichloride):
PCl3 has a trigonal pyramidal shape as well, similar to NCl3, and a lone pair on the phosphorus atom. This shape leads to a non-symmetrical distribution of electrons, causing the molecule to have a dipole moment. Therefore, PCl3 is also polar.
Since only BCl3 has a symmetrical structure with no net dipole, it is the non-polar molecule in this set.