Atomic Timeline

Events

Democritus

400 B.C.

He hypothesized that all matter (plus space and time) is composed of tiny indestructible units, called atoms.

No experiments were done, only based his theories on previous on other philosophers findings.

John Dalton

1803

John Dalton, in the early 1800's, who determined that each chemical element is composed of a unique type of atom, and that the atoms differed by their masses.
Dalton did gas / pressure experiments of different elements, particularly Hydrogen.

Michael Faraday

1832

Responsible for discovering the laws of electrolysis and for popularizing terminology such as anode, cathode, electrode, and ion.
Faraday did electrical experiments. In 1832, he proved that the electricity induced by a magnet, voltaic electricity produced by a battery and static electricity were all the same. He also did significant work in electrochemistry, stating the First and Second Laws of Electrolysis.

J. Plucker

1859

Plucker interpreted the effect of the magnetic field as evidence that whatever produced this glow is electrically charged. The rays given off by the cathode can be deflected by a magnetic field in a direction which suggests that these cathode rays are negatively charged.
Plucker experiment with the cathode ray or tubes used to focus a beam of electrons deflected by electric or magnetic fields to create the image on a television.

Lothar Meyer

1864

Meyer worked on the classification of the elements. He worked on recalculating a number of atomic weights and made use of the periodic table for predicting and studying related elements' chemical properties.
Meyer listed the elements in increasing weight order with elements with the same valence in a given column. Similar to Mendeleev who became his partner with Robert Bunsen.

Dmitri Mendeleev

1869

Dmirtri Mendeleev a Russian chemist sought out to was arranging the elements based on atomic mass into a periodic table.
Using his periodic table, Mendeleev predicted the existence and properties of new chemical elements. When these elements were discovered, his place in the history of science was assured.

G.J. Stoney

1874

Stoney suggested electricity was made of negative particles. He called these electrons.
Stoney calculated the magnitude of the atom using the kinetic theory of gas. From his work the term "electron" was coined.

Sir William Crookes

1879

Sir William Crookes was a british chemist and physicist known for his discovery of the element thallium and his studies on the cathode rays which has been fundamental in the development of atomic physics.
Crookes invented what is known as the Crookes tube which is an electrical discharge tube with a partial vacuum where the the rays of electrons were discovered.

Albert Einstein

1905

Albert Einstein became famous for the theory of relativity, which laid the basis for the release of atomic energy.

Ernest Rutherford

1911

Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure.

Niels Bohr

1922

Niels Bohr model of the atom is very small, positively charged nucleus which contains proton and neutron surrounded by negatively charged electrons. This negatively charged electrons travel in circular orbits around the nucleolus.Niels Bohr atomic model was an improved model from an earlier cubic model, the plum-pudding model, the saturation model, and the Rutherford model.

James Chadwick

1932

James Chadwick played a vital role in the atomic theory, as he discovered the Neutron in atoms. Neutrons are located in the center of an atom, in the nucleus along with the protons.