Draw the Lewis dot structure of PF3 Which atom is at the center of the molecule? b. Is there any lone pair on the central atom? What is the shape of the molecule? d. Is there any resonance hybrid? What is the formal charge of the phosphorus atom?
The Correct Answer and Explanation is:
Lewis Dot Structure of PF₃:
Structure:
rCopyEdit F
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F — P — F
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- Phosphorus (P) is at the center.
- Three fluorine (F) atoms are bonded to phosphorus.
- Phosphorus also has one lone pair of electrons.
a. Central Atom
The central atom is Phosphorus (P) because phosphorus is less electronegative than fluorine, so it is placed at the center, with the more electronegative fluorine atoms arranged around it.
b. Lone Pairs on Central Atom
Yes, there is one lone pair on the central phosphorus atom. Phosphorus has five valence electrons, and three are used to form bonds with three fluorine atoms, leaving two electrons (one lone pair) on phosphorus.
c. Shape of the Molecule
The shape of PF₃ is trigonal pyramidal. This is due to the presence of three bonding pairs and one lone pair on phosphorus. According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, lone pairs repel more strongly than bonding pairs, which causes the molecule to adopt a trigonal pyramidal geometry to minimize repulsion.
d. Resonance Hybrid
No, there is no resonance hybrid in PF₃. Resonance occurs when multiple valid Lewis structures can be drawn by shifting electrons or bonds. In PF₃, the positions of the atoms and electrons are fixed, so only one valid structure exists.
e. Formal Charge of Phosphorus Atom
The formal charge (FC) is calculated as:
FC = Valence electrons – (Lone pair electrons + ½ Bonding electrons)
For phosphorus in PF₃:
- Valence electrons = 5
- Lone pair electrons = 2
- Bonding electrons = 6 (each P-F bond has 2 electrons, total of 3 bonds)
FC = 5 – (2 + 6 ÷ 2) = 5 – (2 + 3) = 0
So, the formal charge on phosphorus is zero.
Conclusion
PF₃ has phosphorus at the center, one lone pair on the central atom, a trigonal pyramidal shape, no resonance structures, and the formal charge on phosphorus is zero. The structure follows standard VSEPR predictions.
