In the correct Lewis Structure for NBr3, how many lone pairs (unshared pairs) are on the central atom? Give all atoms zero formal charge, N in middle surrounded by Br’s
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The correct answer and explanation is :
In the Lewis structure of NBr₃ (Nitrogen Trbromide), the central nitrogen atom will have 1 lone pair of electrons. Here’s a step-by-step explanation of how to arrive at this conclusion:
1. Count the total number of valence electrons:
- Nitrogen (N) is in Group 15 of the periodic table, so it has 5 valence electrons.
- Bromine (Br) is in Group 17, so each bromine atom has 7 valence electrons.
- For NBr₃, there are 3 bromine atoms, so the total valence electrons from bromine are $3 \times 7 = 21$.
- Total number of valence electrons in NBr₃ = 5 (from nitrogen) + 21 (from bromine) = 26 electrons.
2. Determine the bonding arrangement:
- Nitrogen is the central atom because it is less electronegative than bromine.
- Each bromine atom will form a single bond with nitrogen, using 2 electrons per bond.
- There are 3 bromine atoms, so 3 single bonds are formed with nitrogen, using up 3 × 2 = 6 electrons.
3. Distribute the remaining electrons:
- After forming the bonds, there are 26 total valence electrons − 6 electrons used in bonding = 20 electrons remaining.
- These remaining 20 electrons will be placed as lone pairs on the bromine atoms, because bromine can accommodate up to 3 lone pairs.
- Each bromine will get 3 lone pairs, using up 18 electrons (3 × 6 = 18).
- The remaining 2 electrons will be placed as a lone pair on nitrogen.
4. Check formal charges:
- Nitrogen typically follows the octet rule and has 8 electrons around it in total (3 bonds and 1 lone pair), which gives it a formal charge of zero.
- Each bromine also has 8 electrons around it (1 bond and 3 lone pairs), resulting in a formal charge of zero for each bromine atom.
Final structure:
- Nitrogen (N) has 1 lone pair.
- Each Bromine (Br) has 3 lone pairs.
Thus, in the Lewis structure of NBr₃, the central nitrogen atom has 1 lone pair of electrons.
Answer: 1 lone pair
This arrangement minimizes formal charges and follows the octet rule, ensuring stability for the molecule.