Draw the Lewis structure for BrF3. What is the formal charge on the bromine atom?
The correct answer and explanation is:
Correct Answer:
The Lewis structure of BrF₃ (bromine trifluoride) shows three bonding pairs and two lone pairs around the central bromine (Br) atom. The formal charge on the bromine atom in BrF₃ is 0.
Explanation (Approximately 300 Words):
To draw the Lewis structure of BrF₃, we begin by determining the total number of valence electrons:
- Bromine (Br) is in group 17 → 7 valence electrons
- Fluorine (F) is also in group 17 → 7 valence electrons each × 3 = 21
Total valence electrons = 7 (Br) + 21 (3 F) = 28 electrons
Step 1: Skeleton Structure
Place bromine in the center (less electronegative than fluorine), and attach the three fluorine atoms around it using single bonds. Each single bond uses 2 electrons × 3 = 6 electrons.
Remaining electrons: 28 − 6 = 22 electrons
Step 2: Complete Octets of Fluorine Atoms
Each fluorine needs 6 more electrons (3 lone pairs).
3 F × 6 = 18 electrons used
Remaining electrons: 22 − 18 = 4 electrons
Step 3: Place Remaining Electrons on Central Atom
Place the remaining 4 electrons (2 lone pairs) on bromine.
Now bromine has:
- 3 bonding pairs (from the Br–F bonds)
- 2 lone pairs
→ 5 regions of electron density → Trigonal bipyramidal electron geometry
→ T-shaped molecular geometry
Step 4: Determine Formal Charge on Bromine
Formal charge = Valence − (Lone electrons + ½ Bonding electrons)
- Valence electrons of Br = 7
- Lone electrons on Br = 4
- Bonding electrons = 6 (3 bonds × 2 electrons)
Formal charge = 7 − (4 + 3) = 0
Conclusion
The correct Lewis structure shows a T-shaped BrF₃ molecule, and the formal charge on bromine is 0, meaning it’s in its most stable, neutral form in this structure.