1. Convert milligrams to grams:

* There are 1000 milligrams (mg) in 1 gram (g).

* 500.00 mg = 500.00 mg * (1 g / 1000 mg) = 0.50000 g

2. Calculate the molar mass of calcium:

* The molar mass of calcium (Ca) is 40.08 g/mol (found on the periodic table).

3. Use the molar mass to convert grams to moles:

* moles of Ca = (mass of Ca in grams) / (molar mass of Ca)

* moles of Ca = (0.50000 g) / (40.08 g/mol) = 0.01248 mol

Therefore, there are approximately 0.01248 moles of calcium atoms in 500.00 mg of calcium.