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400 BCE
Democritus
He came up with the idea that all matter consisted of tiny, indivisible particles. -
John Dalton
Proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Dmitri Mendeleev
Created the first Periodic Table. The Periodic Law states that when elements are arranged according to their atomic number, elements with similar properties will appear at regular intervals. -
Eugene Goldstein
He discovered protons with the experiments he did with cathode rays which would knock electrons of atoms and attract them to a positively charged electrode. -
J.J. Thomson
Discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. He also studied positively charged particles in neon gas. -
Max Planck
He originated the quantum theory of energy and contributed to the understanding of atomic and subatomic processes. -
Robert Millikan
His oil drop experiment helped to quantify the charge of an electron, which contributed to our understanding of the structure of the atom and atomic theory. -
Ernest Rutherford
He demonstrated that the atom has a tiny and heavy nucleus, and designed an experiment to use the alpha particles from a radioactive element to uncover the idea of atomic structure. -
Niels Bohr
He created a model that shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. -
Werner Heisenberg
Provided research and application to the uncertainty principle and theory of quantum mechanics, -
Erwin Schrödinger
Used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. -
James Chadwick
Discovered the Neutron in atoms.
