Ionic compound formation chart displaying cations and anions.

This image shows a blank ionic compound formation table. The task is to fill in each cell with the correct chemical formula of the ionic compound formed by combining the cation (row) and anion (column).

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## 🔑 Key Principle: Charge Balance

Ionic compounds must be electrically neutral. That means:

> Total positive charge = Total negative charge

To do this, we use the criss-cross method:
- Take the absolute value of the cation’s charge → becomes the subscript of the anion.
- Take the absolute value of the anion’s charge → becomes the subscript of the cation.
- Simplify subscripts if possible (reduce to lowest whole numbers).
- Omit “1” as a subscript.

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## 🧪 Step-by-step Solution

We’ll go row by row, column by column.

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✔ Row 1: Na⁺ (Sodium ion, +1)

| Anion | Formula | Explanation |
|---------------|---------------|-----------|
| SO₄²⁻ | Na₂SO₄ | 2×(+1) + (-2) = 0 |
| NO₃⁻ | NaNO₃ | (+1) + (-1) = 0 |
| PO₄³⁻ | Na₃PO₄ | 3×(+1) + (-3) = 0 |
| CO₃²⁻ | Na₂CO₃ | 2×(+1) + (-2) = 0 |
| SO₃²⁻ | Na₂SO₃ | 2×(+1) + (-2) = 0 |
| NO₂⁻ | NaNO₂ | (+1) + (-1) = 0 |

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✔ Row 2: Mg²⁺ (Magnesium ion, +2)

| Anion | Formula | Explanation |
|---------------|---------------|-----------|
| SO₄²⁻ | MgSO₄ | (+2) + (-2) = 0 |
| NO₃⁻ | Mg(NO₃)₂ | (+2) + 2×(-1) = 0 → parentheses needed for polyatomic |
| PO₄³⁻ | Mg₃(PO₄)₂ | 3×(+2) + 2×(-3) = 6 - 6 = 0 |
| CO₃²⁻ | MgCO₃ | (+2) + (-2) = 0 |
| SO₃²⁻ | MgSO₃ | (+2) + (-2) = 0 |
| NO₂⁻ | Mg(NO₂)₂ | (+2) + 2×(-1) = 0 |

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✔ Row 3: Co³⁺ (Cobalt(III) ion, +3)

| Anion | Formula | Explanation |
|---------------|---------------|-----------|
| SO₄²⁻ | Co₂(SO₄)₃ | 2×(+3) + 3×(-2) = 6 - 6 = 0 |
| NO₃⁻ | Co(NO₃)₃ | (+3) + 3×(-1) = 0 |
| PO₄³⁻ | CoPO₄ | (+3) + (-3) = 0 |
| CO₃²⁻ | Co₂(CO₃)₃ | 2×(+3) + 3×(-2) = 6 - 6 = 0 |
| SO₃²⁻ | Co₂(SO₃)₃ | 2×(+3) + 3×(-2) = 6 - 6 = 0 |
| NO₂⁻ | Co(NO₂)₃ | (+3) + 3×(-1) = 0 |

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✔ Row 4: NH₄⁺ (Ammonium ion, +1)

| Anion | Formula | Explanation |
|---------------|---------------|-----------|
| SO₄²⁻ | (NH₄)₂SO₄ | 2×(+1) + (-2) = 0 |
| NO₃⁻ | NH₄NO₃ | (+1) + (-1) = 0 |
| PO₄³⁻ | (NH₄)₃PO₄ | 3×(+1) + (-3) = 0 |
| CO₃²⁻ | (NH₄)₂CO₃ | 2×(+1) + (-2) = 0 |
| SO₃²⁻ | (NH₄)₂SO₃ | 2×(+1) + (-2) = 0 |
| NO₂⁻ | NH₄NO₂ | (+1) + (-1) = 0 |

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✔ Row 5: K⁺ (Potassium ion, +1)

Same as Na⁺ — both are +1 alkali metals.

| Anion | Formula |
|---------------|---------------|
| SO₄²⁻ | K₂SO₄ |
| NO₃⁻ | KNO₃ |
| PO₄³⁻ | K₃PO₄ |
| CO₃²⁻ | K₂CO₃ |
| SO₃²⁻ | K₂SO₃ |
| NO₂⁻ | KNO₂ |

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✔ Row 6: Cu²⁺ (Copper(II) ion, +2)

Same as Mg²⁺ — both are +2 ions.

| Anion | Formula |
|---------------|---------------|
| SO₄²⁻ | CuSO₄ |
| NO₃⁻ | Cu(NO₃)₂ |
| PO₄³⁻ | Cu₃(PO₄)₂ |
| CO₃²⁻ | CuCO₃ |
| SO₃²⁻ | CuSO₃ |
| NO₂⁻ | Cu(NO₂)₂ |

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✔ Row 7: Al³⁺ (Aluminum ion, +3)

Same as Co³⁺ — both are +3 ions.

| Anion | Formula |
|---------------|---------------|
| SO₄²⁻ | Al₂(SO₄)₃ |
| NO₃⁻ | Al(NO₃)₃ |
| PO₄³⁻ | AlPO₄ |
| CO₃²⁻ | Al₂(CO₃)₃ |
| SO₃²⁻ | Al₂(SO₃)₃ |
| NO₂⁻ | Al(NO₂)₃ |

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✔ Row 8: Ba²⁺ (Barium ion, +2)

Same as Mg²⁺ and Cu²⁺ — all +2.

| Anion | Formula |
|---------------|---------------|
| SO₄²⁻ | BaSO₄ |
| NO₃⁻ | Ba(NO₃)₂ |
| PO₄³⁻ | Ba₃(PO₄)₂ |
| CO₃²⁻ | BaCO₃ |
| SO₃²⁻ | BaSO₃ |
| NO₂⁻ | Ba(NO₂)₂ |

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## ✔ Final Answer Table:

Here's the completed table:

| Cation \ Anion | SO₄²⁻ | NO₃⁻ | PO₄³⁻ | CO₃²⁻ | SO₃²⁻ | NO₂⁻ |
|----------------|---------------|----------------|----------------|---------------|---------------|----------------|
| Na⁺ | Na₂SO₄ | NaNO₃ | Na₃PO₄ | Na₂CO₃ | Na₂SO₃ | NaNO₂ |
| Mg²⁺ | MgSO₄ | Mg(NO₃)₂ | Mg₃(PO₄)₂ | MgCO₃ | MgSO₃ | Mg(NO₂)₂ |
| Co³⁺ | Co₂(SO₄)₃ | Co(NO₃)₃ | CoPO₄ | Co₂(CO₃)₃ | Co₂(SO₃)₃ | Co(NO₂)₃ |
| NH₄⁺ | (NH₄)₂SO₄ | NH₄NO₃ | (NH₄)₃PO₄ | (NH₄)₂CO₃ | (NH₄)₂SO₃ | NH₄NO₂ |
| K⁺ | K₂SO₄ | KNO₃ | K₃PO₄ | K₂CO₃ | K₂SO₃ | KNO₂ |
| Cu²⁺ | CuSO₄ | Cu(NO₃)₂ | Cu₃(PO₄)₂ | CuCO₃ | CuSO₃ | Cu(NO₂)₂ |
| Al³⁺ | Al₂(SO₄)₃ | Al(NO₃)₃ | AlPO₄ | Al₂(CO₃)₃ | Al₂(SO₃)₃ | Al(NO₂)₃ |
| Ba²⁺ | BaSO₄ | Ba(NO₃)₂ | Ba₃(PO₄)₂ | BaCO₃ | BaSO₃ | Ba(NO₂)₂ |

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## 💡 Notes:

- Parentheses are used around polyatomic ions when their subscript is >1 (e.g., (NO₃)₂, not NO₃₂).
- Subscripts are reduced to simplest whole numbers (e.g., Mg₂SO₄₂ → MgSO₄).
- All formulas reflect neutral compounds.

Let me know if you’d like the names of these compounds too!