Which of the following molecules is non-polar in nature?

Concept:

Polar and non-polar molecules - Polarity is the distribution of charge over the atoms of a molecule joined by a bond.

• Based on polarity molecules are divided into two categories - polar and non-polar.
• The molecules with differences in the electronegativities of their atom are having some net dipole moment and are called polar molecules.
• Non-polar molecules have a net dipole moment of zero as the dipole moment of exactly opposite bonds in the molecule cancel each other.

Explanation:

• Nonpolar molecules are those which has a net dipole moment of zero.
• As dipole moment is a vector quantity, the overall dipole moment of a molecule is the sum of dipoles of all the bonds present in the molecule.
• Thus the exactly equal and opposite bonds constitute a net dipole zero.

The calculation for net dipole moment in given molecules - 

SbCl₅ : 

SbCl₅ has trigonal bipyramidal geometry having axial and equatorial bonds. It has a net dipole moment of zero as - 

• Axial bonds have a bond angle of 180° which constitutes two exactly equal and opposite bonds. Hence dipole moment is zero.
• Equatorial bonds also have net dipole zero as the dipole moment of one equatorial Sb-Cl bond is the resultant of the vector sum of the other two equatorial Sb-Cl bonds.

So, the net vector summation of bond moments will be zero so SbCl₅ is a non-polar molecule.

In the other given molecules, the net dipole moment is not zero because -

• In NO₂, there is non-symmetry in the structure.
• In POCl₃, there is a difference in electronegativity of Cl and O atoms.
• In CH₂O, O atom is more highly electronegative than the H atom.

Thus, the only nonpolar molecule is SbCl5.

Hence, the correct answer is option 4.