Formula Writing Chemistry Example 1

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Example 1

easy
Write the chemical formula for aluminum chloride using the charges of the ions: Al3+\text{Al}^{3+} and Cl−\text{Cl}^-.

Solution

  1. 1
    Aluminum has a charge of +3+3 and chlorine has a charge of −1-1.
  2. 2
    To balance the charges, we need 3 chloride ions for every 1 aluminum ion: 3×(−1)=−33 \times (-1) = -3 balances +3+3.
  3. 3
    The formula is AlCl3\text{AlCl}_3. The subscript 3 on Cl indicates three chloride ions per formula unit.

Answer

AlCl3\text{AlCl}_3
When writing ionic compound formulas, the total positive charge must equal the total negative charge so the compound is electrically neutral. The crisscross method (using charge magnitudes as subscripts) is a quick shortcut.

About Formula Writing

The systematic process of combining element symbols and numerical subscripts to represent the exact composition of a chemical compound, ensuring that the total positive charge.

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More Formula Writing Examples

Example 2 medium

Write the chemical formula for calcium phosphate using the crisscross method. Calcium forms [formula

Example 3 medium

Write the correct chemical formulas for: (a) iron(III) sulfate, (b) ammonium carbonate.

Example 4 hard

A student writes the formula for magnesium nitride as [formula]. Explain why this is incorrect and d

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