Historical development of Atomic Model

Events

Democritus

400 B.C

atomic theory posited that all matter is made up small indestructible units he called atoms.

Isaac Newton

1704

theorised a mechanical universe with small, solid masses in motion.

John Dalton

1803

proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.

Michael Faraday

1832

developed the two laws of electrochemistry.

J.Plucker

1859

built one of the first cathode-ray tubes.

Dmitri Mendeleev

1869

created the periodic table

James Clerk Maxwell

1873

proposed the theory of electromagnetism and made the connection between light and electromagnetic waves.

G.J. Stoney

1874

theorised that electricity was comprised of negative particles he called electrons.

Sir William Crookes

1879

experiments with cathode-ray tubes led him to confirm the work of earlier scientists by definitively demonstrating that cathode-rays have a negative charge.

E. Goldstein

1886

discovered canal rays, which have a positive charge equal to an electron.

Wilhelm Roentgen

1895

discovered x-rays.

Henri Becquerel

1896

discovered radiation by studying the effects of x-rays on photographic film

J.J. Thomson

1897

determined the charge to mass ratio of electrons.

Rutherford

1898

discovered alpha, beta, and gamma rays in radiation

Marie Sklodowska Curie

1898

discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium.

Frederick Soddy

1900

came up with the term "isotope" to explain the unintentional breakdown of radioactive elements.

Max Planck

1900

proposed the idea of quantization to explain how a hot, glowing object emitted light.

Hantaro Nagaoka

1903

proposed an atomic model called the Saturnian Model to describe the structure of an atom.

Richard Abegg

1904

found that inert gases have a “stable electron configuration

Hans Geiger

1906

invented a device that could detect alpha particles.

H.G.J. Moseley

1914

discovered that the number of protons in an element determines its atomic number.

Francis William Aston

1919

used a mass spectrograph to identify 212 isotopes.

Niels Bohr

1922

proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.

Louis de Broglie

1923

proposed that electrons have a wave/particle duality.

Cockcroft / Walton

1929

created the first nuclear reaction, producing alpha particles

Paul Dirac

1930

proposed the existence of anti-particles.

James Chadwick

1932

discovered neutrons, particles whose mass was close to that of a proton.

Lise Meitner, Hahn, Strassman

1938

discovered nuclear fission.

Glenn Seaborg

1941 - 51

discovered eight transuranium elements.

Enrico Fermi

1942

created the first man-made nuclear reactor.