Atomic History

Aristotle 200

300

Aristotle thought that there was a limit to the quantity of time matter could be divided. As his experiment he used the four elements: air, fire, earth, and water.

Democritus 100

400

Democirtus thought that all matter consists of small particles, which couldn’t be separated. He called these atoms. He also had the idea that there were different types of atoms with specific sets of properties.

John Dalton Sept 6, 1766- July 27, 1844

Oct 30, 1803

John Dalton pictured atoms as small, indestructible particles without any inner structure. Dalton had several theories for different things:
*He believed all the elements are made up of tiny indivisible particles, known as atoms.
*Atoms of the same element are identical to their weight/
*Atoms of different elements are different from each other and can be identified by their relative weights.

J.J. Thomson Dec 18, 1856- Aug 30, 1940

Oct 30, 1897

J.J. Thomson is credited for discovery of the electron and of isotopes. The discovery of the electron led to his “plum-pudding” model. He pictured the model with electrons on a positive electric charge.

Hantaro Nagaoka Aug 15, 1865-Dec 11, 1950.

Oct 30, 1904

Hantaro Nagoaka suggested that an atom has a central nucleus. Also, that the electrons move in orbits resembling the rings around Saturn. In addition, Hantaro created the Saturnian model.

Ernest Marsden 19 Feb 1889-15 Dec. 1970

Oct 31, 1909

Ernest Marsden is known for helping Ernest Rutherford, and the discovery of a new and enhanced atom. Marsden was one of Rutherford’s students and chose Marsden to assist him with research on an experiment: the gold foil experiment.

Robert Milikan March 22, 1868- Dec 19, 1953

Nov 1, 1910

One of Milikan’s earlier successes was the accurate determination of the charge carried by an electron using the elegant “falling-drop method”. He also proved or discovered that this number was a constant for all electrons, as a result representing the atomic structure of electricity.

Ernest Rutherford Aug 30, 1871- Oct 19, 1937.

Oct 30, 1911

Ernest Rutherford said that an atom has a positively charged nucleus and is very dense. Also, electrons move fast, and in random motion. How Rutherford discovered this is with the gold foil experiment.

Niels Bohr Oct 7, 1885- Nov 18, 1962

Oct 30, 1913

Niels Bohr adapted onto Ernest Rutherford’s nuclear structure. Bohr’s model focused on the electrons, which move in spherical orbits at fixed distances from the nucleus. Additionally, he introduced the idea that an electron could drop from a higher-energy orbit to a lower one when an electron loses energy or vice versa.

Henry Moseley Nov 23, 1887- Aug 10, 1915

Nov 2, 1913

Used x-ray diffraction to show that each element has its own atomic number.

Louis de Broglie 1892-1987.

Oct 30, 1924

Louis de Broglie proposed that there are moving particles like electrons have some properties of waves.

Erwin Schrodinger Aug 12, 1887-Jan 4, 1961

Oct 30, 1926

Erwin Schrodinger developed mathematical equations to describe motion of electrons in atoms. Schrodinger created the electron cloud model.

James Chadwick Oct 20, 1891- July 24, 1974

Oct 30, 1932

James Chadwick is the discoverer of the neutron, which have no charge. Atmoic nuclei contain neutrons and positively charged protons.

From 100A.D. to 1935A.D.

Period: Oct 30, 2000 to Oct 30, 1935