You're asked to write the
chemical formulas for the given ionic compounds, based on their names which include the oxidation state (Roman numerals) of the metal.
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🔑 Key Concept:
In ionic compounds, the
total positive charge must balance the total negative charge. The Roman numeral tells you the charge on the metal ion. You then combine it with the anion (non-metal ion), using subscripts to make the compound neutral.
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## Let’s solve each one:
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1. Iron(II) oxide
- Iron(II) → Fe²⁺
- Oxide → O²⁻
→ Charges: +2 and -2 → they cancel directly.
✔ Formula:
FeO
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2. Iron(III) oxide
- Iron(III) → Fe³⁺
- Oxide → O²⁻
→ Need to balance +3 and -2 → LCM is 6.
- 2 Fe³⁺ = +6
- 3 O²⁻ = -6
✔ Formula:
Fe₂O₃
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3. Lead(II) chloride
- Lead(II) → Pb²⁺
- Chloride → Cl⁻
→ Need 2 Cl⁻ to balance Pb²⁺.
✔ Formula:
PbCl₂
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4. Lead(IV) iodide
- Lead(IV) → Pb⁴⁺
- Iodide → I⁻
→ Need 4 I⁻ to balance Pb⁴⁺.
✔ Formula:
PbI₄
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5. Cobalt(II) chloride
- Cobalt(II) → Co²⁺
- Chloride → Cl⁻
→ Need 2 Cl⁻ to balance Co²⁺.
✔ Formula:
CoCl₂
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6. Cobalt(III) chloride
- Cobalt(III) → Co³⁺
- Chloride → Cl⁻
→ Need 3 Cl⁻ to balance Co³⁺.
✔ Formula:
CoCl₃
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##
✔ Final Answers:
| Compound | Chemical Formula |
|-----------------------|------------------|
| iron(II) oxide |
FeO |
| iron(III) oxide |
Fe₂O₃ |
| lead(II) chloride |
PbCl₂ |
| lead(IV) iodide |
PbI₄ |
| cobalt(II) chloride |
CoCl₂ |
| cobalt(III) chloride |
CoCl₃ |
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Let me know if you’d like to see how to name them from formulas too!
Parent Tip: Review the logic above to help your child master the concept of naming compounds practice worksheet.
