Final answer:
To find the number of moles in 3.9x10²⁰ magnesium atoms, divide the number of atoms by Avogadro's number resulting in approximately 6.47x10⁻⁴ moles.
Step-by-step explanation:
To calculate the number of moles of magnesium in 3.9x1020 atoms, we can use Avogadro's number, which is 6.022x1023 atoms per mole. The calculation is as follows:
Number of moles = Number of atoms ÷ Avogadro's number
Number of moles = 3.9x1020 atoms ÷ 6.022x1023 atoms/mol
Number of moles = 0.647x10-3 moles, or 6.47x10-4 moles of magnesium
This calculation shows how to convert atoms to moles and is essential in stoichiometry, particularly when dealing with chemical reactions, such as combining magnesium with oxygen to form magnesium oxide (MgO).