Wilhelm Konrad Röntgen made an earth-shattering discovery for chemistry and atoms in 1895: He discovered x rays. Then, soon after, Henri Becquerel took the idea of x rays a step further and made another, equally earth-shattering discovery for chemistry and atoms: radioactivity. The Curies figured out which known elements were radioactive. Rutherford categorized radioactive rays into alpha, beta, and gamma. We explore what these rays are. We end up with the discovery of the neutron.