1. PI₃
- Phosphorus (P) has 5 valence electrons.
- Each iodine (I) has 7 valence electrons.
- Total valence electrons: 5 + 3(7) = 26.
- Phosphorus is the central atom, bonded to three iodine atoms.
- Each P-I bond uses 2 electrons, so 3 bonds use 6 electrons.
- Remaining electrons: 26 - 6 = 20.
- Distribute 3 lone pairs (6 electrons) to each iodine (3 iodines × 6 electrons = 18 electrons).
- Remaining 2 electrons go to phosphorus as a lone pair.
- Phosphorus has 3 bonds (6 electrons) and 1 lone pair (2 electrons), totaling 8 electrons (octet rule satisfied).
- Each iodine has 1 bond (2 electrons) and 3 lone pairs (6 electrons), totaling 8 electrons (octet rule satisfied).
- Lewis structure: P bonded to three I atoms, each I has three lone pairs, and P has one lone pair.
2. N₂
- Each nitrogen (N) has 5 valence electrons.
- Total valence electrons: 2(5) = 10.
- Two nitrogen atoms form a triple bond (6 electrons).
- Remaining electrons: 10 - 6 = 4.
- Each nitrogen has one lone pair (2 electrons).
- Each nitrogen has 3 bonds (6 electrons) and 1 lone pair (2 electrons), totaling 8 electrons (octet rule satisfied).
- Lewis structure: N≡N with one lone pair on each nitrogen.
3. H₂O
- Oxygen (O) has 6 valence electrons.
- Each hydrogen (H) has 1 valence electron.
- Total valence electrons: 6 + 2(1) = 8.
- Oxygen is the central atom, bonded to two hydrogen atoms.
- Each O-H bond uses 2 electrons, so 2 bonds use 4 electrons.
- Remaining electrons: 8 - 4 = 4.
- Distribute 2 lone pairs (4 electrons) to oxygen.
- Oxygen has 2 bonds (4 electrons) and 2 lone pairs (4 electrons), totaling 8 electrons (octet rule satisfied).
- Each hydrogen has 1 bond (2 electrons), satisfying the duet rule.
- Lewis structure: O bonded to two H atoms, with two lone pairs on oxygen.
Parent Tip: Review the logic above to help your child master the concept of octet rule worksheet.
