Law of Definite Proportions

• For a given compound, the elements always combine in the same proportion.
• For example
• A sodium chloride molecule (NaCl) is always a 1:1 ratio of one sodium atom to one chlorine atom.
• A 100.0 g sample of NaCl contains 39.3 g Na and 60.7 g Cl.

Mass Cl = 60.7 g = 1.54

Mass Na 39.3 g

• A 58.44.0 g sample of NaCl contains 22.99 g Na and 35.44 g Cl.

Mass Cl = 35.44 g = 1.54

Mass Na 22.99 g