Mole Day runs from 6:02 AM to 6:02 PM October 23. A mole is 6.02 x 10^23 (Avogadro's number) of objects. The mole is useful because it allows a chemist to count by weighing. For example, one mole of hydrogen atoms (H) and one mole of chlorine (Cl) atoms each contain 6.02 x 10^23 particles. They will react to form hydrogen chloride (HCl). H + Cl --> HCl. The atomic weights of H and Cl are 1 and 35.45 respectively. Therefore 1 g (gram) H and 35.45 g Cl will react to form 36.45 g HCl. You could also use pounds, tons, etc. Google Mole Day for more information.