Question

For molecules of general formula${\mathbf{AX}}_n$ (where n > 2), how do you determine if a particular molecule is polar?

Short answer

Polar bonds are formed when atoms with very high electronegativity difference combine. If the bonds are oriented in such a way that the resultant dipole moment of the molecule is not zero, then it is a polar molecule.

Step-by-step solution

Polarity and dipole moment.

Due to high electronegativity difference between atoms in a molecule, opposite charges develop on atoms. This charge separation is known as polarity.

Dipole moment is the measure of polarity. It is the product between the charge developed and the distance between the opposite charges.It is represented by.

$\text{μ=\hspace{0.17em}d\hspace{0.17em}×\hspace{0.17em}q}$

Where,

d = distance between opposite charges,

q = charge

Polar molecule

For the general formula ${\text{AX}}_{\text{n}}$ if the bonds are oriented in such a way that the resultant dipole moment is not zero, then the molecule is polar. Example of such a molecule is ${\text{NH}}_{\text{3}}$. Structure of ${\text{NH}}_{\text{3}}$is given below.

The dipole moment for the bond is directed towards the nitrogen atom. As shown in the diagram the resultant dipole moment is not zero as the dipole moments do not cancel each other. Thus is a polar molecule.