Chemical Naming WITH Answer KEY (at bottom) - Chemical Formula ... - Free Printable

You're looking at a Chemical Formula Writing Worksheet that teaches how to combine cations (positive ions) and anions (negative ions) to form neutral ionic compounds.

The goal is to write the correct chemical formula for each combination so that the total positive charge equals the total negative charge — making the compound electrically neutral.

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## ✔ How to Solve These Problems: The Criss-Cross Method

1. Identify the charges of the cation and anion.
- For example: Sodium (Na⁺) and Chloride (Cl⁻)
2. Criss-cross the charges (ignore the + and – signs) to become subscripts.
- Na⁺ and Cl⁻ → Na₁Cl₁ → just NaCl
3. Simplify subscripts if possible (e.g., Mg²⁺ and O²⁻ → Mg₂O₂ → simplify to MgO).
4. Polyatomic ions or multivalent metals: Pay attention to Roman numerals (like Iron(II) = Fe²⁺, Iron(III) = Fe³⁺).

> 💡 Important Note: The worksheet already provides the answers in red — it’s likely meant as a practice sheet with answer key included.

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## 🧪 Let’s Break Down a Few Examples

Example 1: Magnesium (Mg²⁺) + Chloride (Cl⁻)

- Charge: +2 and -1
- Criss-cross: Mg₁Cl₂ → MgCl₂

Example 2: Iron(III) (Fe³⁺) + Oxide (O²⁻)

- Charge: +3 and -2
- Criss-cross: Fe₂O₃ → Fe₂O₃

Example 3: Silver (Ag⁺) + Sulfide (S²⁻)

- Charge: +1 and -2
- Criss-cross: Ag₂S → Ag₂S

> ⚠️ The note says “The combining power of silver is 1 and zinc is 2” — this means:
> - Silver (Ag) always has a +1 charge (monovalent)
> - Zinc (Zn) always has a +2 charge (divalent)

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## 🔍 Set 1 Highlights

| Cation | Anion | Formula | Why? |
|-------------|----------|-------------|-------------------------------------------|
| Sodium (Na⁺)| Oxide (O²⁻) | Na₂O | 2×(+1) + 1×(-2) = 0 |
| Calcium (Ca²⁺)| Nitride (N³⁻) | Ca₃N₂ | 3×(+2) + 2×(-3) = 0 |
| Aluminum (Al³⁺)| Sulfide (S²⁻) | Al₂S₃ | 2×(+3) + 3×(-2) = 0 |

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## 🔍 Set 2 Highlights

| Cation | Anion | Formula | Why? |
|---------------|-------------|-------------|--------------------------------------------|
| Lithium (Li⁺) | Phosphide (P³⁻) | Li₃P | 3×(+1) + 1×(-3) = 0 |
| Lead(IV) (Pb⁴⁺) | Bromide (Br⁻) | PbBr₄ | 1×(+4) + 4×(-1) = 0 |
| Copper(I) (Cu⁺) | Oxide (O²⁻) | Cu₂O | 2×(+1) + 1×(-2) = 0 |
| Nickel(II) (Ni²⁺) | Phosphide (P³⁻) | Ni₃P₂ | 3×(+2) + 2×(-3) = 0 |

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## 📌 Key Concepts Reinforced:

- Ionic compounds are neutral → total positive charge = total negative charge.
- Subscripts indicate number of atoms.
- Roman numerals tell you the charge of transition metals (e.g., Iron(II) = Fe²⁺, Iron(III) = Fe³⁺).
- Some elements have fixed charges (Group 1 = +1, Group 2 = +2, Al = +3, Zn = +2, Ag = +1).

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## ✔ Final Answer:

✔ All formulas in the worksheet are correctly written using the criss-cross method to ensure charge neutrality.

If you were asked to *fill in* the blanks, you would use the steps above. Since the worksheet already shows the answers in red, it serves as a self-checking tool or answer key.

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## 🎯 Tip for Learning:

Practice writing formulas without looking at the answers first. Then check your work. This reinforces understanding of ionic bonding and valence charges.

Let me know if you’d like to practice generating formulas from scratch — I can give you blank versions or quiz you!