Atomic Theory

Democritus

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Democritus was born about 460 BCE.He was one of the first to discover atoms that are present in the atmosphere.These are about atoms that come in different forms.The scientific community knew that he was one of the first to realise atoms.

Isaac Newton

Jan 1, 1704

Proposed a mechanical universe with small solid masses in motion.

John Dalton

Jan 1, 1803

English chemist who stated the Atomic Theory whichstated that all matter was composed of small indivisibleparticles called atoms.

Micheal Faraday

Oct 19, 1832

Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday himself was not a proponent of atomism

J. Plucker

Oct 19, 1859

Built one of the first gas discharge tubes

Dmitri Mendeleeff

Oct 19, 1869

Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights".

G.J Stoney

Oct 19, 1879

Proposed that electricity was made of discrete negative particles he called "electrons".

J.J Thompson

Feb 18, 1898

First to measure the electron. Developed theplum-pudding model of the atom. Describes the atom as aslightly positive sphere with small electrons inside.

Soddy

Oct 19, 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.

Ernest Rutherford

Feb 9, 1911

Inferred a small, dense, positively-charged nucleus as theresult of the alpha particle scattering gold foil experiment.

H.G.J Mosely

Oct 19, 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"

Francis William Aston

Oct 20, 1919

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

De Brogile

Oct 20, 1923

Discovered that electrons had a dual nature-similar to both particles and waves.

Enrico Fermi

Oct 20, 1942

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

Neils Bohr

Feb 9, 1949

A Danish physicist who stated that electrons could onlyorbit the nucleus in succesively larger orbits around thenucleus. The outer orbits could hold more electrons.