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Lewis Structure Worksheet

General chemistryGrades 10–12 · GCSE / A-level / IB · AP Chemistry · Intro college chemistry5 items · answer key included

This Lewis structure worksheet takes students through 17 molecules and ions step by step: count the total valence electrons, decide how many bonding pairs and lone pairs sit on the central atom, draw the Lewis dot structure, then work out formal charges and resonance. It starts with simple octet molecules (H2O, NH3, CO2, HCN), moves to polyatomic ions such as nitrate, carbonate and sulfate, and finishes with expanded octets (PCl5, SF6, XeF4) and an incomplete octet (BF3). Short resonance and formal charge questions follow, and the full answer key makes it easy to use as drawing Lewis structures practice, homework or a printable PDF quiz.

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Lewis Structure Worksheet

Name Class Date

Part A — Simple molecules and ions

Complete each row. 'Bonding pairs' means shared electron pairs around the central atom (a double bond counts as 2). Draw the full Lewis structure, including all lone pairs.

1.
SpeciesTotal valence electronsBonding pairs (central atom)Lone pairs (central atom)Draw the Lewis structureFormal charges / resonance notes
H₂O822H–O–H; O has 2 lone pairsAll formal charges 0
NH₃831N bonded to 3 H; 1 lone pair on NAll formal charges 0
CH₄840C bonded to 4 HAll formal charges 0
CO₂1640O=C=O; 2 lone pairs on each OAll formal charges 0
HCN1040H–C≡N; 1 lone pair on NAll formal charges 0
N₂103 (each N)1 (each N):N≡N:All formal charges 0
H₂CO1240H₂C=O; 2 lone pairs on OAll formal charges 0
BF₃2430B bonded to 3 F; 3 lone pairs on each FIncomplete octet on B (6 electrons); all formal charges 0
NH₄⁺840[N bonded to 4 H]⁺ in bracketsN +1; H 0

Part B — Resonance, formal charge and expanded octets

Complete each row. Show formal charges on the structure and state how many resonance structures there are.

2.
SpeciesTotal valence electronsBonding pairs (central atom)Lone pairs (central atom)Draw the Lewis structureFormal charges / resonance notes
O₃1831O=O–O; central O has 1 lone pairCentral O +1, single-bonded O −1; 2 resonance structures
SO₂1831O=S–O; S has 1 lone pairOctet form: S +1, single-bonded O −1; 2 resonance structures (expanded form O=S=O has all charges 0)
NO₃⁻2440N with one N=O and two N–O; in brackets with 1− chargeN +1, each single-bonded O −1; 3 equivalent resonance structures
CO₃²⁻2440C with one C=O and two C–O; in brackets with 2− chargeEach single-bonded O −1, C 0; 3 equivalent resonance structures
SO₄²⁻324 (octet form)0S with 4 S–O single bonds; in brackets with 2− chargeOctet form: S +2, each O −1. Form with two S=O minimises formal charge (S 0, two O −1; 6 resonance forms)
PCl₅4050P bonded to 5 Cl; 3 lone pairs on each ClExpanded octet (10 electrons on P); all formal charges 0
SF₆4860S bonded to 6 F; 3 lone pairs on each FExpanded octet (12 electrons on S); all formal charges 0
XeF₄3642Xe bonded to 4 F; 2 lone pairs on XeExpanded octet (12 electrons on Xe); all formal charges 0

Part C — Resonance questions

Answer each question in the space provided.

3.
Draw both resonance structures of ozone, O3. Both O–O bonds in ozone are 128 pm long. Explain why, and give the O–O bond order.
O=O+–O− ↔ −O–O+=O. The real molecule is a resonance hybrid, so the π electrons are delocalised over both bonds; each O–O bond has a bond order of 1.5, so both are the same length (between an O–O single and an O=O double bond).
4.
Draw the three resonance structures of the carbonate ion, CO32−. What is the C–O bond order, and what is the average formal charge on each oxygen?
In each structure one O is double-bonded (formal charge 0) and two are single-bonded (formal charge −1); the double bond rotates among the three oxygens. C–O bond order = 4 bonds ÷ 3 = 4/3 (≈1.33); average formal charge on each O = −2 ÷ 3 = −2/3.
5.
For the thiocyanate ion, SCN− (16 valence electrons), calculate the formal charges in the structures [S=C=N]− and [S≡C–N]−. Which structure contributes more?
[S=C=N]−: S 0, C 0, N −1. [S≡C–N]−: S +1, C 0, N −2. The first structure contributes more: its formal charges are smaller and the negative charge sits on N, the most electronegative atom.

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Answer key: Lewis Structure Worksheet

Part A — Simple molecules and ions

1.
SpeciesTotal valence electronsBonding pairs (central atom)Lone pairs (central atom)Draw the Lewis structureFormal charges / resonance notes
H₂O822H–O–H; O has 2 lone pairsAll formal charges 0
NH₃831N bonded to 3 H; 1 lone pair on NAll formal charges 0
CH₄840C bonded to 4 HAll formal charges 0
CO₂1640O=C=O; 2 lone pairs on each OAll formal charges 0
HCN1040H–C≡N; 1 lone pair on NAll formal charges 0
N₂103 (each N)1 (each N):N≡N:All formal charges 0
H₂CO1240H₂C=O; 2 lone pairs on OAll formal charges 0
BF₃2430B bonded to 3 F; 3 lone pairs on each FIncomplete octet on B (6 electrons); all formal charges 0
NH₄⁺840[N bonded to 4 H]⁺ in bracketsN +1; H 0

Part B — Resonance, formal charge and expanded octets

2.
SpeciesTotal valence electronsBonding pairs (central atom)Lone pairs (central atom)Draw the Lewis structureFormal charges / resonance notes
O₃1831O=O–O; central O has 1 lone pairCentral O +1, single-bonded O −1; 2 resonance structures
SO₂1831O=S–O; S has 1 lone pairOctet form: S +1, single-bonded O −1; 2 resonance structures (expanded form O=S=O has all charges 0)
NO₃⁻2440N with one N=O and two N–O; in brackets with 1− chargeN +1, each single-bonded O −1; 3 equivalent resonance structures
CO₃²⁻2440C with one C=O and two C–O; in brackets with 2− chargeEach single-bonded O −1, C 0; 3 equivalent resonance structures
SO₄²⁻324 (octet form)0S with 4 S–O single bonds; in brackets with 2− chargeOctet form: S +2, each O −1. Form with two S=O minimises formal charge (S 0, two O −1; 6 resonance forms)
PCl₅4050P bonded to 5 Cl; 3 lone pairs on each ClExpanded octet (10 electrons on P); all formal charges 0
SF₆4860S bonded to 6 F; 3 lone pairs on each FExpanded octet (12 electrons on S); all formal charges 0
XeF₄3642Xe bonded to 4 F; 2 lone pairs on XeExpanded octet (12 electrons on Xe); all formal charges 0

Part C — Resonance questions

3.
O=O+–O− ↔ −O–O+=O. The real molecule is a resonance hybrid, so the π electrons are delocalised over both bonds; each O–O bond has a bond order of 1.5, so both are the same length (between an O–O single and an O=O double bond).
4.
In each structure one O is double-bonded (formal charge 0) and two are single-bonded (formal charge −1); the double bond rotates among the three oxygens. C–O bond order = 4 bonds ÷ 3 = 4/3 (≈1.33); average formal charge on each O = −2 ÷ 3 = −2/3.
5.
[S=C=N]−: S 0, C 0, N −1. [S≡C–N]−: S +1, C 0, N −2. The first structure contributes more: its formal charges are smaller and the negative charge sits on N, the most electronegative atom.

How to use this worksheet

  1. Model one row (e.g. CO₂) on the board before students start: valence electron total → skeleton → complete octets → move lone pairs into multiple bonds if needed.
  2. 'Bonding pairs' counts shared electron pairs around the central atom, so a double bond counts as 2 and a triple bond as 3.
  3. For ions, remind students to add electrons for negative charges, subtract for positive charges, and draw the final structure in square brackets with the charge.
  4. Follow up with the VSEPR molecular geometry worksheet — the lone-pair counts here feed straight into shape prediction.
  5. Set the title, student lines and answer option on the left, then press Download PDF and choose “Save as PDF” (or print directly). Your choices are remembered on this device.

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Frequently asked questions

How do you draw a Lewis structure step by step?

Add up the valence electrons of all atoms (adjusting for charge), put the least electronegative atom in the centre, join atoms with single bonds, complete the octets of outer atoms with lone pairs, place any remaining electrons on the central atom, and convert lone pairs into double or triple bonds if the central atom still lacks an octet.

How do you calculate formal charge?

Formal charge = valence electrons − lone-pair (non-bonding) electrons − ½ × bonding electrons. The best Lewis structure has formal charges as close to zero as possible, with any negative charge on the most electronegative atom.

What are resonance structures?

Resonance structures are two or more valid Lewis structures that differ only in where electrons are placed. The real molecule is a hybrid of them, so in nitrate or carbonate all three C–O or N–O bonds are identical with a bond order of 4/3.

Which atoms can have an expanded octet?

Elements in period 3 and below (such as P, S, Cl and Xe) can hold more than eight electrons around them, as in PCl5 (10), SF6 (12) and XeF4 (12). Period 2 elements such as C, N, O and F never exceed an octet.

Is there an answer key for this Lewis structure worksheet?

Yes. The answer key lists the valence electron total, bonding and lone pairs on the central atom, a description of each structure, the formal charges and the number of resonance forms.

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