How did the discovery of atoms explain the observation that the mass of the products always equals the mass of the reactants in a reaction?

Okay well gravitational energy is matter forced by gravity making energy though the kinetic energy then the electric energy produces electricity from the kinetic energy and the kinetic energy gets its energy from the gravitational energy. was that the answer you wanted or something else?  

Is there an image with it

Answer ozone (o3) is made of three atoms of oxygen, it is a molecule;