Lewis Structures Practice Worksheet - Free Printable

1) PBr₃:
- Phosphorus (P) has 5 valence electrons. Each bromine (Br) has 7 valence electrons.
- Total valence electrons = 5 + 3×7 = 26.
- P is central atom, bonded to three Br atoms with single bonds (using 6 electrons).
- Remaining 20 electrons are placed as lone pairs: 3 lone pairs on each Br (18 electrons) and 1 lone pair on P (2 electrons).
- Structure: P with three single bonds to Br, each Br has three lone pairs, P has one lone pair.

2) N₃H₂ (likely meant to be N₂H₂, diazene; assuming N₂H₂):
- Two nitrogen atoms (each 5 valence e⁻) and two hydrogen atoms (each 1 valence e⁻).
- Total valence electrons = 2×5 + 2×1 = 12.
- Structure: H–N=N–H, with a double bond between nitrogens.
- Each N has one lone pair. Each H has no lone pairs.
- (Note: If truly N₃H₂, it’s an unusual species; standard is N₂H₂ for hydrazine analogs.)

3) CH₃OH:
- Carbon (4), oxygen (6), four hydrogens (4×1) → total valence electrons = 4+6+4 = 14.
- C bonded to three H and one O; O bonded to C and one H.
- Bonds: C–H (three), C–O, O–H → 5 single bonds = 10 electrons used.
- Remaining 4 electrons go as two lone pairs on oxygen.
- Structure: Tetrahedral carbon, oxygen with two lone pairs and two single bonds.

4) NO₂⁻:
- Nitrogen (5), two oxygens (2×6), plus one extra electron from charge → total = 5+12+1=18.
- Resonance structures: N central, double bond to one O, single bond to other O (with negative charge).
- Lone pairs: Double-bonded O has two lone pairs; single-bonded O has three lone pairs and negative charge; N has one lone pair.
- Average bond order 1.5; actual structure is resonance hybrid.

5) C₂H₄:
- Two carbons (2×4), four hydrogens (4×1) → total valence electrons = 8+4=12.
- Double bond between two carbons; each carbon bonded to two hydrogens.
- All atoms have full octets (carbons via double bond and two single bonds; hydrogens via single bonds).
- Structure: H₂C=CH₂, planar, with each C having three regions of electron density.