Question

Which one of the following molecules has the lowest bond length (in pm)?

• A. \(F_2\)
• B. \(Cl_2\)
• C. HF
• D. \(Br_2\)
• E. \(O_2\)

Hint:

Hydrogen bonds are almost always the shortest because Hydrogen has no inner core electrons and only one small electron shell.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bond length depends on the size of the atoms involved in the bond and the bond order (multiplicity).
Smaller atoms form shorter bonds.

Step 3: Detailed Explanation:
Compare the sizes of the atoms:
1. \(F_2, Cl_2, Br_2\): These are single bonds between large halogen atoms. Size increases as \(F < Cl < Br\).
2. \(O_2\): This has a double bond which shortens the distance, but Oxygen atoms are still larger than Hydrogen atoms.
3. HF: Hydrogen is the smallest atom in the periodic table (radius \(\approx 37 \text{ pm}\)). Fluorine is the smallest halogen.
Because Hydrogen is so tiny, any bond it forms (especially with another small atom like Fluorine) will be exceptionally short.
Actual values: \(HF \approx 92 \text{ pm}\), \(O_2 \approx 121 \text{ pm}\), \(F_2 \approx 142 \text{ pm}\).

Step 4: Final Answer:
HF has the lowest bond length.