Question

Among the following, the molecule that will have the highest dipole moment is:

• A. H$_2$
• B. HI
• C. HBr
• D. HCl
• E. HF

Hint:

Trend for dipole moment: $\text{HF}>\text{HCl}>\text{HBr}>\text{HI}$. Always check the electronegativity difference for diatomic molecules.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
Dipole moment depends on the electronegativity difference between the bonded atoms and the distance between them.
Step 2: Key Formula or Approach:
Dipole moment ($\mu$) = charge ($q$) $\times$ distance ($d$).
For hydrogen halides, $q$ depends on the electronegativity difference.
Step 3: Detailed Explanation:
H$_2$ is non-polar, so $\mu = 0$.
For HX (where X is a halogen), the electronegativity decreases in the order: $\text{F}>\text{Cl}>\text{Br}>\text{I}$.
The electronegativity difference ($\Delta EN$) is highest for HF.
Greater electronegativity difference results in greater partial charges, and thus a higher dipole moment.
Even though bond length increases down the group, the magnitude of charge dominates the trend in this case.
Step 4: Final Answer:
HF has the highest dipole moment.