Lewis Structure Worksheet #1 featuring hand-drawn Lewis structures for molecules in Groups A, B, and C, including CH₄, NH₃, H₂O, SiF₄, NCl₃, PO₄³⁻, ClO₃⁻, ClO₄⁻, SO₃²⁻, H₂CO, HCN, CO, and CO₂.

The image you've uploaded is a Lewis Structure Worksheet #1 for a chemistry class (Chem 50), completed by a student named Naomi Rosario. The worksheet asks students to draw Lewis structures for various molecules and polyatomic ions, and the student has already drawn the structures.

Let’s go through each molecule/ionic species, verify the correctness of the Lewis structures, explain the reasoning, and point out any potential issues or corrections if needed.

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🔍 General Rules for Drawing Lewis Structures:

1. Count total valence electrons.
2. Place the least electronegative atom in the center (except H).
3. Connect atoms with single bonds (each bond = 2 electrons).
4. Distribute remaining electrons as lone pairs.
5. Ensure all atoms satisfy the octet rule (H only needs 2 electrons).
6. Use double/triple bonds if needed to satisfy octets.
7. For ions, add/remove electrons based on charge.

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## ✔ Group A

| Molecule | Valence e⁻ | Student's Structure | Evaluation |
|--------|------------|---------------------|----------|
| CH₄ (Methane) | 8e⁻ (C:4, H×4:4) |  | ✔ Correct. Carbon bonded to 4 H atoms; no lone pairs. Octet satisfied. |
| NH₃ (Ammonia) | 8e⁻ (N:5, H×3:3) |  | ✔ Correct. Nitrogen has 3 single bonds and one lone pair. Octet complete. |
| H₂O (Water) | 8e⁻ (O:6, H×2:2) |  | ✔ Correct. Oxygen has two bonds and two lone pairs. Octet satisfied. |
| SiF₄ (Silicon tetrafluoride) | 32e⁻ (Si:4, F×4:28) |  | ✔ Correct. Si bonded to four F atoms; each F has 3 lone pairs. All atoms have octets. |
| NCl₃ (Nitrogen trichloride) | 26e⁻ (N:5, Cl×3:21) |  | ✔ Correct. N bonded to three Cl atoms, one lone pair on N. Each Cl has 3 lone pairs. |

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## ✔ Group B

| Ion | Valence e⁻ | Student's Structure | Evaluation |
|------|------------|---------------------|----------|
| PO₄³⁻ (Phosphate) | 32e⁻ (P:5, O×4:24, +3 from charge) |  | ⚠️ Incorrect — Missing formal charges and double bond. Should have one P=O double bond and three P–O⁻ single bonds. The structure shown shows all single bonds, which gives incorrect formal charges. <br> Correct: One double bond to O, three single bonds to O⁻, and lone pairs accordingly. |
| ClO₃⁻ (Chlorite ion) | 26e⁻ (Cl:7, O×3:18, +1 from charge) |  | ⚠️ Incomplete — This structure shows only single bonds, but it should have one Cl=O double bond and two Cl–O⁻ bonds. Also, formal charges not indicated. |
| ClO₄⁻ (Perchlorate) | 32e⁻ (Cl:7, O×4:24, +1 from charge) |  | ⚠️ Incorrect — Should have one Cl=O double bond and three Cl–O⁻ single bonds, or resonance forms. As drawn, all single bonds imply high formal charge on Cl. |
| SO₃²⁻ (Sulfite ion) | 26e⁻ (S:6, O×3:18, +2 from charge) |  | ⚠️ Incorrect — Should have one S=O double bond, two S–O⁻ single bonds, and a lone pair on S. The drawing shows all single bonds, which is invalid. |

> 💡 Note: For polyatomic ions like PO₄³⁻, ClO₃⁻, ClO₄⁻, SO₃²⁻, resonance structures are important. These often involve double bonds to minimize formal charges.

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## ✔ Group C

| Molecule | Valence e⁻ | Student's Structure | Evaluation |
|--------|------------|---------------------|----------|
| H₂CO (Formaldehyde) | 12e⁻ (C:4, O:6, H×2:2) |  | ✔ Correct. Carbon double bonded to O, single bonded to two H atoms. No lone pairs on C. O has two lone pairs. Octets satisfied. |
| HCN (Hydrogen cyanide) | 10e⁻ (H:1, C:4, N:5) |  | ✔ Correct. Triple bond between C and N, single bond to H. Lone pair on N. Octet on C and N. |
| CO (Carbon monoxide) | 10e⁻ (C:4, O:6) |  | ✔ Correct. Triple bond between C and O, plus one lone pair on each atom. Note: This gives formal charges: C: -1, O: +1, but it’s the most stable structure due to triple bond. |
| CO₂ (Carbon dioxide) | 16e⁻ (C:4, O×2:12) |  | ✔ Correct. Double bonds between C and each O. Each O has two lone pairs. C has no lone pairs. Octets satisfied. |

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❗ Summary of Corrections Needed

| Molecule/Ion | Issue | Correction |
|-------------|------|-----------|
| PO₄³⁻ | All single bonds, missing double bond | Add one P=O double bond, three P–O⁻ single bonds; show formal charges |
| ClO₃⁻ | All single bonds, missing double bond | Add one Cl=O double bond, two Cl–O⁻ bonds |
| ClO₄⁻ | All single bonds | Add one Cl=O double bond, three Cl–O⁻ bonds |
| SO₃²⁻ | All single bonds | Add one S=O double bond, two S–O⁻ bonds, lone pair on S |

> 🔄 Resonance: These ions have multiple resonance structures. For example, PO₄³⁻ has four resonance forms, each with the double bond on a different oxygen.

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✔ Final Assessment

- Group A: All correct ✔
- Group B: All structures are incomplete or incorrect due to missing double bonds and formal charges ✘
- Group C: All correct ✔

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✔ Recommended Fixes for Group B:

#### PO₄³⁻:
```
O⁻
|
O=P=O
|
O⁻
```
(One double bond, three single bonds to O⁻, and lone pairs on O atoms)

#### ClO₃⁻:
```
O⁻
|
O=Cl
|
O⁻
```
(One double bond, two single bonds to O⁻)

#### ClO₄⁻:
```
O⁻
|
O=Cl=O
|
O⁻
```
(One double bond, three single bonds to O⁻)

#### SO₃²⁻:
```
O⁻
|
O=S=O
|
O⁻
```
(One double bond, two single bonds to O⁻, lone pair on S)

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📝 Conclusion

Naomi Rosario did an excellent job on Groups A and C, correctly drawing simple covalent molecules.

However, Group B contains errors because she didn't include double bonds or formal charges, which are essential for accurate Lewis structures of polyatomic ions.

✔ Recommendation: Review how to assign formal charges and use double bonds to minimize them in polyatomic ions.

Let me know if you'd like a corrected version of the entire worksheet!