Now with the atomic weight information we can consider matching up atoms on a mass-to-mass basis. Let's take hydrogen chloride, HCl. One hydrogen atom is attached to one chlorine atom, but they have different masses. A hydrogen atom has a mass of 1.008 AMU and a chlorine atom has a mass of 35.453 AMU. Practically speaking, one AMU is far too small a mass for us to weigh in the lab. We could weigh 1.008 grams of hydrogen and 35.453 grams of chlorine, and they would match up exactly right. There would be the same number of hydrogen atoms as chlorine atoms. They could join together to make HCl with no hydrogen or chlorine left over. If we take one gram of a material for every AMU of mass in the atoms of just one of them, we will have a mol (or mole) of that material. One mol of any material, therefore, has the same number of particles of the material named, this number being Avogadro's number, 6.022 E 23.