. List the rules for writing the formula for an ionic compound.

When writing the formula for an ionic compound, there are several key rules to follow: 1. **Identify the Ions**: Determine the cation (positively charged ion) and the anion (negatively charged ion) that will combine to form the ionic compound. 2. **Charge Balance**: The total positive charge from the cations must balance the total negative charge from the anions. This means that the sum of the charges must equal zero. 3. **Use of Subscripts**: If the charges of the cation and anion are not equal, use subscripts to indicate the number of each ion needed to achieve charge balance. The subscript is written as a small number to the right of the chemical symbol. 4. **Simplify Ratios**: If the ratio of cations to anions can be simplified, do so. For example, if you have two cations and three anions, the formula would be written as \( \text{A}_2\text{B}_3 \). 5. **No Need for Charges in the Formula**: When writing the formula, do not include the charges of the ions. The formula should only reflect the ratio of the ions. 6. **Order of Ions**: The cation is always written first, followed by the anion. For example, in sodium chloride, the formula is written as \( \text{NaCl} \). 7. **Polyatomic Ions**: If the compound contains polyatomic ions (ions made up of more than one atom), treat the polyatomic ion as a single unit. Use parentheses if more than one of the polyatomic ion is needed. For example, in calcium nitrate, the formula is \( \text{Ca(NO}_3\text{)}_2 \). 8. **Naming Conventions**: When naming the compound, the cation retains its elemental name, while the anion's name is modified (usually by adding "-ide" for simple anions, or using the name of the polyatomic ion). By following these rules, you can accurately write the formula for any ionic compound.