Q.13
Molecule that has no lone pair of electrons on the central atom (among the choices) is:
BF3 No Lone Pairs Central Atom XeF4 PF3 ClF3
BF3 is the correct answer: Boron trifluoride (BF3) has no lone pairs on the central boron atom.
Lewis Structure Analysis
Central atom lone pairs determine molecular geometry via VSEPR theory. Count valence electrons and bonding.
- XeF4: Xenon (8 valence e⁻) + 4F (28 e⁻) = 36 e⁻ total. 4 Xe-F bonds (8 e⁻), 2 lone pairs on Xe. Has lone pairs.
- PF3: Phosphorus (5 valence e⁻) + 3F (21 e⁻) = 26 e⁻. 3 P-F bonds (6 e⁻), 1 lone pair on P. Has lone pair.
- ClF3: Chlorine (7 valence e⁻) + 3F (21 e⁻) = 28 e⁻. 3 Cl-F bonds (6 e⁻), 2 lone pairs on Cl. Has lone pairs.
- BF3: Boron (3 valence e⁻) + 3F (21 e⁻) = 24 e⁻. 3 B-F bonds (6 e⁻), 0 lone pairs on B (electron deficient). Correct.
Option Explanations
| Molecule | Central Atom | Bonds | Lone Pairs | Status |
|---|---|---|---|---|
| XeF4 | Xe | 4 | 2 | ❌ |
| PF3 | P | 3 | 1 | ❌ |
| ClF3 | Cl | 3 | 2 | ❌ |
| BF3 | B | 3 | 0 | ✅ |
Molecule No Lone Pairs Central Atom – GATE Chemistry Solution
BF3 stands alone as the molecule with no lone pairs on its central boron atom among XeF4, PF3, ClF3 options—crucial GATE Life Sciences chemistry question testing VSEPR theory and Lewis structures.
Why BF3 Has Zero Lone Pairs
Boron in BF3 uses all 3 valence electrons for bonding, forming trigonal planar geometry with no remaining electrons for lone pairs. Other molecules have excess valence electrons forming lone pairs.
GATE Exam Tip
Remember: Group 13 central atoms (B, Al) often electron-deficient with no lone pairs, unlike pnictogens/chalcogens.
