1. Find the molar mass of calcium chloride (CaCl₂):

* Calcium (Ca) has a molar mass of 40.08 g/mol.

* Chlorine (Cl) has a molar mass of 35.45 g/mol.

* CaCl₂ has a molar mass of 40.08 + (2 * 35.45) = 110.98 g/mol

2. Calculate the number of moles of CaCl₂:

* Moles = Mass / Molar mass

* Moles = 654.5 g / 110.98 g/mol

* Moles = 5.89 mol CaCl₂

3. Determine the number of moles of chloride ions:

* Since there are two chloride ions (Cl⁻) for every one molecule of CaCl₂, you have twice the number of moles of chloride ions: 5.89 mol CaCl₂ * 2 mol Cl⁻/mol CaCl₂ = 11.78 mol Cl⁻

4. Calculate the number of chloride atoms:

* Use Avogadro's number (6.022 x 10²³ atoms/mol) to convert moles of chloride ions to atoms: 11.78 mol Cl⁻ * 6.022 x 10²³ atoms/mol = 7.09 x 10²⁴ chloride atoms

Therefore, there are approximately 7.09 x 10²⁴ chloride atoms in 654.5 grams of calcium chloride.