Atomic Theory Scientists

Democritus

460

460 BC Greece He developed the idea of atoms. He thought that at some point, a substance wouldn’t be able to be split in half anymore and he called these basic matter particles ‘atoms’. Without this idea of atoms, none of the discoveries of atoms or elements would have been made since they didn’t have a base to work on. http://www.nobeliefs.com/atom.htm

Isaac Newton

Jan 1, 1704

1704 England The book “Opticks” was released. It included context about atoms and forces between atoms. All change is caused by collisions of atoms. This showed that atoms could move and cause things to move as well. www.phys.virginia.edu/classes/252/atoms.html http://www.spaceandmotion.com/Physics-Sir-Isaac-Newton.htm

John Dalton

Jan 1, 1803

1803 England He started using symbols to represent the atoms of different elements. The logbook entry called Observations on the Ultimate Particles of Bodies and their Combinations had the first use of symbols to represent the elements in modern chemistry. Soon, he had a table of elements arranged by atomic mass. We can easily determine an element by the symbol and we know that they have different atomic masses. http://www.wired.com/science/discoveries/news/2008/09/dayintech_0903

George Johnstone Stoney

Jan 1, 1894

1894 Ireland He wrote a letter titled Of the “Electron”, or Atom of Electricity to the editors of the Philosophical magazine. He calls a definite quantity of electricity E¬r which is later developed to be an ‘electron’. Also, he estimates the mass of an electron. We know the mass on an electron and that it is a definite quantity of electricity. www.chemteam.info/Chem-History/Stoney-1894.html http://particleadventure.org/other/history/sciencet.html

Joseph John Thomson

Jan 1, 1897

1897 England He discovered that atoms contained electrons through his explorations on the properties of cathode rays. He concluded that the rays were composed of very light, negatively charged particles. We now know that an atom contains electrons and we know the structure of an electron cloud and how many electrons each shell of the cloud can hold. http://en.wikipedia.org/wiki/J._J._Thomson

Max Planck

Jan 1, 1900

1900 Germany He developed the Quantum theory. He attempted to draw conclusions from the heat radiation to the radiating atom. The discovery of quanta changed the idea of physics, because it showed that established ideas about the nature of radiation and energy were wrong. www.spaceandmotion.com/quantum-theory-max-planck-quotes.htm http://www.thebigview.com/spacetime/quantumtheory.html

Hantaro Nagaoka

Jan 1, 1903

1903 Japan He was the first scientist to present a Saturnian model of an atom. The model displayed a nucleus containing positive electric charge and electrons ‘orbiting’ it. It gave us an idea of what an atom looked like, making it easier to understand the structure of it. http://www.japanese-greatest.com/technology/atomic-model.html

Robert Andrews Millikan

Jan 1, 1909

1909 United States of America He worked on an oil-drop experiment which they used to measure the charge on an electron. The experiment was conducted by using charged oil droplets and suspending it between two metal plates. Since the electric field was known, the charge on the oil drops could be determined when the drops are held at a stable position. We are able to measure the charge of a single electron as a result of his experiment. http://en.wikipedia.org/wiki/Robert_Andrews_Millikan http

Ernest Rutherford

Jan 1, 1911

1911 England He made up the Rutherford model, stating that a very small positively charged nucleus was orbited by electrons. It supported Nagaoka’s model of the atom. http://en.wikipedia.org/wiki/Ernest_Rutherford

Henry Gwyn Jefferys Moseley

Jan 1, 1914

1914 England He found a relationship between and element’s X-ray length and its atomic number. Before he discovered this, the atomic numbers were just sequential numbers based on the element’s atomic weight. It showed that there was a gap between atomic numbers 43 and 61 in the table. It shows that the atomic numbers of the elements aren’t just numbers based on the element’s weight but has connection with the element’s X-ray length. http://www.lycos.com/info/henry-moseley--elements.html http

Niels Henrik David Bohr

Jan 1, 1922

1922 Denmark He was awarded the Nobel Prize in physics for his in the investigation of the atom’s structure and the radiation that is sent out from them. We have more knowledge about the atom’s structure and about the radiation that is emitted from it. http://en.wikipedia.org/wiki/Niels_Bohr

James Chadwick

Jan 1, 1932

1932 England He proved that neutrons existed. Due to the existence of neutrons, we are able to break up Uranium 235 and create atomic bombs. http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html http://www.atomicarchive.com/Bios/Chadwick.shtml