Draw the main Lewis structure of NOF. Draw nonbonding electrons using the dot notation and bonding electrons as a bond. Determine the number of bonding electrons and the number of nonbonding electrons in the structure of BeF2. Enter the number of bonding electrons followed by the number of nonbonding electrons, separated by a comma, in the dot structure of this molecule.
The Correct Answer and Explanation is:
Part 1: Lewis structure of NOF
1. Count valence electrons:
- Nitrogen (N): 5 valence electrons
- Oxygen (O): 6 valence electrons
- Fluorine (F): 7 valence electrons
Total = 5 + 6 + 7 = 18 valence electrons
2. Determine the skeleton:
Nitrogen is less electronegative than oxygen and fluorine, so nitrogen is likely the central atom.
Structure: N – O – F (with bonds between N–O and O–F)
3. Draw single bonds between N–O and O–F:
Each single bond counts as 2 electrons, so 2 bonds = 4 electrons.
Electrons left: 18 – 4 = 14 electrons to distribute as lone pairs.
4. Distribute remaining electrons to satisfy the octet rule:
- Start by completing octets on outer atoms first (F and O):
- Fluorine needs 6 electrons as lone pairs (3 pairs) to complete its octet.
- Oxygen will also have lone pairs.
- Distribute 6 electrons (3 lone pairs) on F:
14 – 6 = 8 electrons left
- Place lone pairs on oxygen:
Oxygen has one bond with N and one with F (2 bonds, 4 electrons), so it needs 4 more electrons (2 lone pairs) to complete octet.
8 – 4 = 4 electrons left
- Place remaining 4 electrons on nitrogen as 2 lone pairs.
5. Check formal charges:
- N: 5 valence electrons originally
Bonds: 2 bonds = 4 electrons shared, lone pairs = 4 electrons
Formal charge = 5 – (4 + 1/2*4) = 5 – (4 + 2) = 5 – 6 = -1 (not ideal) - O and F will have zero formal charge.
Try to reduce formal charges by forming a double bond between N and O:
Change N–O from single to double bond:
Now total bonds are:
- N=O (double bond, 4 electrons)
- O–F (single bond, 2 electrons)
Electrons used in bonds = 6 electrons
Electrons left = 18 – 6 = 12 electrons for lone pairs
Assign:
- F: 3 lone pairs (6 electrons)
- O: 2 lone pairs (4 electrons)
- N: 1 lone pair (2 electrons)
Formal charges:
- N: 5 – (2 + 1/2*4) = 5 – (2 + 2) = 1 (small positive charge)
- O: 6 – (4 + 1/2*6) = 6 – (4 + 3) = -1
- F: 7 – (6 + 1/2*2) = 7 – (6 + 1) = 0
This is acceptable.
Final Lewis structure for NOF:
- N with one lone pair
- N double bonded to O
- O single bonded to F
- F with 3 lone pairs
- O with 2 lone pairs
Part 2: Number of bonding and nonbonding electrons in BeF₂
1. BeF₂ valence electrons:
- Be: 2 valence electrons
- F: 7 valence electrons × 2 = 14
Total = 16 electrons
2. Lewis structure of BeF₂:
- Be is the central atom, bonded to two F atoms (linear molecule)
- Each Be–F bond is a single bond with 2 electrons
- Fluorines complete their octet with 3 lone pairs (6 electrons each)
- Beryllium only has 4 electrons around it (doesn’t complete octet, which is typical for Be)
3. Count electrons:
- Bonding electrons: 2 bonds × 2 electrons = 4 electrons
- Nonbonding electrons: Each F has 6 nonbonding electrons × 2 F atoms = 12 electrons
Answer:
Number of bonding electrons, number of nonbonding electrons in BeF₂ = 4,
The Lewis structure of NOF involves careful consideration of valence electrons and formal charges to find the most stable arrangement. Nitrogen, less electronegative than oxygen and fluorine, serves as the central atom. Starting with 18 valence electrons in total, single bonds are drawn between N-O and O-F, which initially leaves 14 electrons to be distributed as lone pairs. Fluorine, being highly electronegative, receives three lone pairs (6 electrons), and oxygen receives two lone pairs (4 electrons). Initially placing two lone pairs on nitrogen yields a formal charge imbalance. To improve stability, the N-O bond becomes a double bond, adjusting lone pairs and charges accordingly. This double bond reduces formal charges on nitrogen and oxygen, resulting in an acceptable Lewis structure with nitrogen carrying a small positive charge, oxygen a negative charge, and fluorine neutral.
In contrast, the BeF₂ molecule is simpler. Beryllium has only two valence electrons and forms two single bonds with fluorine atoms. Despite beryllium’s typical incomplete octet (with only 4 electrons around it), this structure is stable. Fluorine atoms complete their octets by holding three lone pairs each. Therefore, the total bonding electrons in BeF₂ are from the two single Be-F bonds, contributing 4 bonding electrons. The fluorine atoms contribute 12 nonbonding electrons (6 electrons each). This count confirms the typical Lewis structure for BeF₂ and helps in understanding electron distribution in molecules with electron-deficient central atoms.