Question

A neutral molecule \(XF_{3}\) has a zero dipole moment. The element X is most likely:

• A. chlorine
• B. boron
• C. nitrogen
• D. carbon
• E. bromine

Hint:

Zero dipole moment in \(AX_n\) molecules usually implies the central atom has no lone pairs (e.g., \(BF_3, CH_4, PCl_5, SF_6\)). If there are lone pairs, the symmetry is broken (unless it's a specific case like \(XeF_4\)), resulting in a net dipole.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A molecule has a zero dipole moment if it is perfectly symmetrical, such that the individual bond dipoles cancel each other out. For an \(AF_3\) type molecule to have zero dipole moment, it must have a trigonal planar geometry with no lone pairs on the central atom.

Step 2: Detailed Explanation:
1. Nitrogen (N): In \(NF_3\), nitrogen has 5 valence electrons. It forms 3 bonds and has 1 lone pair. Geometry is Pyramidal. Dipoles do not cancel (\(\mu \neq 0\)).
2. Chlorine/Bromine (Cl/Br): In \(ClF_3\), the central atom has 7 valence electrons. It forms 3 bonds and has 2 lone pairs. Geometry is T-shaped. Dipoles do not cancel (\(\mu \neq 0\)).
3. Boron (B): In \(BF_3\), boron has 3 valence electrons. It forms 3 bonds and has 0 lone pairs. Geometry is Trigonal Planar (120° angles). All bond dipoles cancel perfectly.
4. Carbon (C): Carbon typically forms 4 bonds (\(CF_4\)). A neutral \(CF_3\) molecule would be a radical and not a stable neutral molecule in this context.

Step 3: Final Answer
The element X is boron, forming the symmetrical \(BF_3\) molecule.