-
430 BCE
Democritus
Democritus claimed that atoms were uniform, solid, hard, indestructible, and that they moved in infinite numbers through space. He believed that differences in atomic shape and size determined the properties of matter. -
John Dalton
John Dalton suggested that all matter is made of tiny indivisible particles called atoms. He came to his conclusions through experimentation. He created Dalton's Atomic Theory, of which 3/4 rules remain true today. -
Dmitri Mendeleev
Dmitri Mendeleev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, which led him to the creation of the periodic table of elements. -
Eugene Goldstein
Eugene Goldstein discovered positive particles by experimenting with a tube filled with hydrogen gas. He found the positive particle had a charge equal and opposite to the electron. The positive particle was named the proton. -
J.J Thomson
J.J experimented with cathode ray tubes, which showed every atom has negatively charged subatomic particles (electrons). His model, depicting electrons embedded in a positively charged "soup" was nicknamed the "Plum Pudding Model." -
Max Planck
Max Planck introduced the theory of “quanta”, that is, that radiation consists of quanta with specific energies determined by a new fundamental constant, thereafter called Planck’s constant. This was the first proposition of quantum theory. -
Robert Millikan
Robert Millikan determined the magnitude of the electron's charge. Small electrically charged drops of oil were suspended between two metal plates where they were subjected to the downward force of gravity and the upward attraction of an electrical field. -
Ernest Rutherford
The experiments using the scattering of particles on thin gold foil led Ernest Rutherford to create this model. It shows a central, positively charged nucleus containing most of the mass, surrounded by a cloud of negatively charged particles. -
Niels Bohr
Niels Bohr proposed a structured model of an atom. In this model, the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. -
Werner Heisenberg
Heisenberg developed the uncertainty principle and his theory of quantum mechanics. This theory and the applications of it which resulted in the discovery of allotropic forms of hydrogen. -
Erwin Schrödinger
Erwin Schrödinger used the wave-particle duality of the electron to develop and solve a complex mathematical equation that accurately described the behavior of the electron in a hydrogen atom. -
James Chadwick
James Chadwick is best known for his discovery of the neutron. The neutron is a neutrally charged particle, which occupies the nucleus along with protons.
