Question

Explain why hcl has a smaller dipole moment than hf, even though the h−cl bond is longer than the h−f bond.

Answer 1

Dipole moment measures the polarity of the molecule that is measure of the separation of two opposite charges. Electronegativity difference between the atoms results dipole moment.

Dipole moment of bond is equal to the product of the magnitude of charge and distance between them (charges).

It is given by:

$\mu = e\times d$

where,

$\mu$ = dipole moment

$e$ = magnitude of charge whether partially positive or negative charge.

$d$ = distance between charges.

Since, $H-Cl$ bond distance is larger than the$H-F$ bond distance, because of large partial charge on the atoms of $H-F$; from the definition of dipole moment $H-Cl$ (1.08) has smaller dipole moment than $H-F$ (1.82).