Question: how many chlorine atoms are needed?
Answer: The mass in grams of 6.022 x 1023 atoms of an element is called the molar mass of that element. For elements, the molar mass is an amount in grams that is numerically equal to the atomic weight of the element. Cl2 is a molecule that is made up of two chlorine atoms. Chlorine has an atomic weight of 35.45.