Question

When does the shape of a molecule affect its polarity?

Answer 1

Hint: The polarization of a particle enormously depends upon the shape of the atom. A diatomic atom like \[HF\] referenced above has no issue of shape. The net dipole moment is simply because of the uneven distribution of electrons between the two atoms. However, when there are multiple atoms associated with making a bond, there are numerous complexities.

Complete answer:
Consider each polar bond in a molecule as a little arrow pointing from positive to negative. This tells us that the bond dipole is a vector amount.
Like some other vector amount, the direction is an imperative part of its description. Thus, the calculation of the molecule determines the direction that the bond dipole vectors point.
Example: The water molecule is of bent shape. Subsequently, when the two sets of electrons shared by oxygen with two hydrogen atoms are pulled towards oxygen, the net dipole moment brings the direction of the oxygen atom. There is no other force to cancel the resultant dipole moment. Consequently, the water molecule is highly polar
The polarity of the molecule comes about because of including all these individual bond dipoles.

Note:
The electronegativity difference between carbon and chlorine is adequate enough for the \[C - Cl\] bond to get polarized. The pair of electrons divided among \[C\] and \[Cl\] is more towards the \[Cl\] atoms. Nonetheless, the carbon tetrachloride molecule is of symmetrical tetrahedron shape, which brings about canceling the net dipole moments of the bonds bringing about zero net dipole moments. Consequently, the molecule gets nonpolar.