the number equal to the number of carbon atoms in exactly 12 grams of pure ¹²C: Avogadro's number. One mole represents 6.022 × 10²³ units. The mass of 1 mole of an element is equal to its atomic mass in grams. the number of atoms in exactly 12 g of pure ¹²C, equal to 6.022 × 10²³ atoms.