Define atomic weight and mass, indicate the units as Atomic Mass Units (Dalton's). Calculate the atomic mass of a molecule of water by looking up the atomic mass of each atom in the molecule, using the correct formula for the molecule and adding up the total atomic mass units based on the isotopes. From the molecular formula, define a gram molecular formula. Elicit that this number represents one Mole of a substance. Describe that one mole of a substance contains 6.02 x 10^23 molecules of a substance and he figure is called Avogadro's number. Stress that this number represents one mole of any substance, atoms molecules or particles. Have Ben calculate the atomic mass of iodine solid, a diatomic molecule and indicate it as One Gram Molecular Weight. Determine the number of iodine particles in one mole of iodine vapor.