we know that atoms are extremely tiny but just how tiny are they how many atoms exist within macroscopic objects it's not as difficult as one might think to calculate these numbers with a pretty reasonable degree of certainty we just need to know the mass of a substance as well as its molar mass perhaps you're at a birthday party and you notice a helium balloon and all of a sudden you find yourself consumed with the desire to know how many helium atoms are in the balloon let's say you find out that there's about 0.3 Gams of helium in one balloon that will be enough information to figure this out first we need to convert this mass of helium into a number of moles of helium atoms so let's take our 0.3 G and multiply by 1 mole of helium over 4 G of helium which is the molar mass of helium that gives us 0.078 moles of helium atoms in the balloon we know that a mole of any substance has a number of particles equal to avagadro's number which is 6.022 * 10 23rd that's what makes the mole so useful it applies to any substance so if we multiply the number of moles of helium by avagadro's number we get around 4.7 * 10^ 22 helium atoms that's almost 50 billion trillion so it's more than just a handful of atoms in there let's say someone else had a balloon filled with Xenon another noble gas and they knew that they had 3 2 * 10^ 21 Xenon atoms in the balloon what mass will this be and is it more or less than the mass in the helium balloon well if we divide this number by avagadro's number we get 0.0053 moles of xenon Xenon is 131.35 G of Xenon so even though there are far fewer Xenon atoms in the balloon it still has more than twice the mass of gas as helium and now we can convert between mass and number of particles for an element