Which of the following is FALSE regarding the Lewis structure for PBr5?
A The total number of valence electrons is 40.
B There are unpaired electrons on the central atom.
C There are 5 electron domains around the central atom.
D The formal charge on each atom is zero.
The correct answer and explanation is :
The **correct answer is:
**👉 B. There are unpaired electrons on the central atom. (This is FALSE)
🔍 Explanation (300+ words):
To determine which statement is false, we must understand the Lewis structure of phosphorus pentabromide (PBr₅) and analyze each option step by step.
🔬 1. Lewis Structure of PBr₅:
Phosphorus (P) is the central atom, and it is bonded to five bromine (Br) atoms.
- Phosphorus has 5 valence electrons (group 15).
- Each bromine atom has 7 valence electrons (group 17).
So, the total valence electrons:
= 5 (from P) + 5 × 7 (from 5 Br atoms)
= 5 + 35
= 40 valence electrons ✅
Each Br atom forms a single bond with P, using 2 electrons per bond, totaling 10 electrons for bonding.
The remaining 30 electrons are distributed as lone pairs (3 lone pairs on each Br atom), and the phosphorus atom uses all its valence electrons in bonding.
✅ Option A: “The total number of valence electrons is 40.”
✔️ True – We calculated this above.
❌ Option B: “There are unpaired electrons on the central atom.”
❌ False – In the Lewis structure of PBr₅:
- Phosphorus forms 5 single bonds with each Br.
- That means it uses all 5 valence electrons in bonding.
- There are no unpaired electrons left on the central atom.
✔️ So this statement is false, making it the correct choice for this question.
✅ Option C: “There are 5 electron domains around the central atom.”
✔️ True – Each single bond with a Br counts as one electron domain.
So P has 5 bonding domains, which gives it a trigonal bipyramidal geometry.
✅ Option D: “The formal charge on each atom is zero.”
✔️ True – The formal charges are:
- P: 5 valence electrons – 0 lone pair electrons – 5 bonds = 0
- Br: 7 valence electrons – 6 lone pair electrons – 1 bond = 0
So all atoms have a formal charge of zero.
🧠 Conclusion:
Option B is false because phosphorus in PBr₅ does not have any unpaired electrons—it uses all of them to form bonds with the five bromine atoms.