History of the Atom

Democritus

460

created the first atomic theory; that all matter consists of invisible particles called atoms.

Antoine Laviosier

Apr 25, 1772

he began the conversation on what an atom was exactly.

John Dalton

Apr 25, 1803

helped in the development of the atomic theory and created the first published table of relative atomic weights.

Dmitri Melendeev

Apr 25, 1869

arranged elements into 7 groups with similar properties. he discovered that the properties of elements "were periodic functions of the their atomic weights". this became known as the Periodic Law.

Eugene Goldstein

Apr 25, 1886

observed rays he called "canal rays," which passed through the holes, or channels, in the cathode to strike the glass walls of the tube at the end near the cathode. he figured since the canal rays traveled in the opposite direction from the cathode rays, they must carry the opposite charge.

Max Planck

Apr 25, 1900

used the idea of quanta (discrete units of energy) to explain hot glowing matter.

JJ Thomson

Apr 25, 1906

created the “plum pudding” model of the atom; discovered the electron.

Ernest Rutherford

Apr 25, 1907

designed an experiment to use alpha particles admitted by a radioactive element as probes to the unseen world of atomic structure. the gold foil experiment atom had a tiny, heavy nucleus.

Robert Millikan

Apr 25, 1908

measured the charge on an electron with an apparatus.

Henry Moseley

Apr 25, 1913

a British chemist who studied under Rutherford and developed the application of X-ray spectra to study atomic structure.

Niels Bohr

Apr 25, 1922

developed the Bohr model of the atom; he proposed the theory that energy levels of electrons are discreet and the electrons orbit around the atomic nucleus but can jump from one energy level to another.

Erwin Schrodinger

Apr 25, 1926

viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.

James Chadwick

Apr 25, 1932

discovered the neutron in 1932. inspired the U.S. government to begin serious atomic bomb research efforts due to his discovery.

Robert Boyle

Apr 25, 2014

discussed the possibility of atoms existing. he stressed organization of atoms and is sometimes called the "Father of Chemistry" for his continuous work on materials.