Atomic Structure Timeline

Isaac Newton

1704

Proposed a mechanical universe with small solid masses in motion.

Atomic Structure

Period: 1704 to 1950

John Dalton

1803

proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.

Michael Faraday

1832

studied the effect of electricity on solutions. Came up with and developed the laws of electrolysis, splitting molecules with electricity. was not a proponent of atomism.

J. Plucker

1859

built the cathode ray tube

Lothar Meyer

1864

classified into 6 families by their valance.

Dmitri Mendeleev

1869

arranged the elements into 7 groups. Discovered the periodic law, properties of elements "were periodic functions of their atomic weights."

Sir Williams Crookes

1879

Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.

E. Goldsrtien

1886

Used CRT to study "canal rays"

G.J. Stoney

1894

Proposed electrons

Wilhelm Roentgen

1895

Using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays".

Henri Becquerel

1896

Discovered some chemicals spontaneously decompose and give off very pentrating rays when studying the effect of x-rays on photogenic film.

J.J. Thompson

1897

-Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram. Hear Thompson talk about the size of an atom. Examine Thompson's 3 experiments to verify atoms had parts.
-Studied "canal rays" and found they were associated with the proton H + .

Marie Sklodowska Curie

1898

Studied uranium and thorium and called their decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

Rutherford

1898

Studies radiation from uranium and named them alpha and beta. Estimated atom site and concluded mass was concentrated in the nucleus.

Soddy

1900

Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay.

Max Planck

1900

used idea of quanta to explain hot glowing matter

Nagoka

1903

Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.

Abegg

1904

Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity.

Alber Einstein

1905

E = mc2

Hans Geiger

1906

Developed an electrical device, Geiger Müller tube, to "click" when hit with alpha particles

R.A. Millikan

1909

Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron.

Ernest Rutherford

1911

Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.

H.G.J. Moseley

1914

Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

Aston

1919

Discovered the existence of isotopes through the use of a mass spectrograph.

Niels Bohr

1922

Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.

de Broglie

1923

Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein.

Heisenberg

1927

Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle.

Cockcroft/ Walton

1929

Schrodinger

1930

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

Paul Dirac

1930

Proposed anti-particles . Anderson discovered the anti-electron (positron) in 1932 and Segre/Chamberlain detected the anti-proton in 1955.

James Chadwick

1932

Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.

Lise Meitner, Hahn, Strassman

1938

Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

Enrico Fermi

1942

Conducted the first controlled chain reaction releasing energy from the atoms nucleus.

Glenn Seaborg

1951

Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.

James Clark Maxwell

1973

Proposed electric and magnetic fields filled the void.