This unit is called the mole, and the number of molecules in one mole is equal to 6.02x10^23. The atomic weights listed on the periodic table are given in grams per mole. To find the weight of a fluorine atom in grams, take the atomic weight of fluorine (18.99 grams per mole) and divide it by 6.02x10^23. Learn more about Atoms & Molecules Sources: