To determine the number of atoms present in a given mass of a substance, you need to use Avogadro's number and the molar mass of the substance. Avogadro's number, approximately 6.022 × 10^23, represents the number of particles (atoms, molecules, ions) in one mole of a substance.
The molar mass of helium (He) is approximately 4 grams per mole (g/mol). So, to find the number of atoms in 64 amu (atomic mass units) of helium, you can follow these steps:
Convert the given mass from amu to grams. Since 1 amu is approximately equal to 1.66 x 10^-24 grams, you can calculate:
64 amu * (1.66 x 10^-24 g/amu) = 1.0624 x 10^-22 grams
Calculate the number of moles using the molar mass of helium:
Moles = Mass / Molar mass = 1.0624 x 10^-22 g / 4 g/mol = 2.656 x 10^-23 mol
Finally, use Avogadro's number to determine the number of atoms:
Number of atoms = Moles * Avogadro's number = 2.656 x 10^-23 mol * (6.022 x 10^23 atoms/mol) = 1.5996 atoms (approximately)
Therefore, there are approximately 1.6 atoms present in 64 amu of helium. Please note that since atoms are indivisible units, you cannot have a fraction of an atom.