1) The mole is the amount of substance that contains as many elementary entities as there are atoms in 12 grams of carbon-12. It allows chemists to convert between the number of particles and mass. 2) A formula mass is calculated by adding the atomic masses of each element in a compound's chemical formula. It represents the mass in grams of 1 mole of that substance. 3) Calculations using the mole concept and formula masses allow chemists to determine the masses of reactants and products involved in chemical reactions.