Subsequently, Rutherford established that the nucleus of the hydrogen atom was a positively chargedparticle, for which he coined the name proton in 1920. He also suggested that the nuclei of elements otherthan hydrogen must contain electrically neutral particles with approximately the same mass as the proton.The neutron, however, was not discovered until 1932, when James Chadwick (1891–1974, a student ofRutherford; Nobel Prize in Physics, 1935) discovered it. As a result of Rutherford’s work, it became clearthat an α particle contains two protons and neutrons, and is therefore the nucleus of a helium atom.The historical development of the different models of the atom’s structure is summarized in Figure 1.22.Rutherford’s model of the atom is essentially the same as the modern model, except that it is now knownthat electrons are not uniformly distributed throughout an atom’s volume. Instead, they are distributedaccording to a set of principles described in Chapter 6, "The Structure of Atoms." Figure 1.23shows howthe model of the atom has evolved over time from the indivisible unit of Dalton to the modern viewtaught today.