The Atomic Theory

Aristotle

322

Aristotle did not believe in the atomic theory, and he taught different ways. He did believe that all materials were made of atoms, but atoms of the four elements; water, fire, earth, and air. He thought everything was a smaller combination of these elements, and most people believed him, causing Democritus' theory to be overlooked.
-Obvisouly, everything is not just made of combinations of water, fire, earth, and air. Citations &Picture: http://the-history-of-the-atom.wikispaces.com/Aristotle

Democritus

460

He formulated the basic science understanding of atoms that there is today, and was the first to describe atoms. Through observations, he made his theory that suggested atoms are soild, indestructible, invisible, and homogenous.
-Some problems with his theory were that atoms can actually be divided, and they are not invisible.
citations: http://the-history-of-the

atom.wikispaces.com/Democritus
Picture: same as above

John Dalton

Dec 8, 1803

-December 8th, 1803, John Dalton
-He stated that all matter was made of smaller particles called atoms. Also, Atoms of a single given element are identical in mass and properties. And he stated that compounds are made from a combo of atoms.
-A chemical reaction is because of the rearranging of atoms.
-Atoms actually can be divided, unlike what his theory said.
Citations:http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html
Picture: http://www.rsc.org/

J.J. Thompson

Dec 11, 1897

-In a series of experiments he discovered even smaller particles in the atom called electrons, also discovered isotopes, and also invented the mass spectrometer. He explains that it is difficult for charged ions to attract each other through insulating water molecules, so they dissociate.
-His plum-pudding model represented a sphere of positive matter in which electrons are positioned by electrostatic forces.
-It didn't explain why atoms undergo reactions.

Marie Curie

Dec 11, 1898

Maire Curie worked on radioactivity and reported evidence that supported the fact that there was a radioactive element in pitch blend ores. Then she discovered the radioactive elements Polonium and Radium. She also found that you can exactly measure the strength of uranium.
-There was nothing wrong with her theories, that were all correct and they still stand today.
Citations: http://www.aip.org/history/curie/resbr1.htm
Picture: same as above -Her theories do not have any problems, they

Ernest Rutherford

Jul 11, 1909

His atomic theory proposed that an atom has a centreal positive nucleus with negative electrons oribiting the nucleus. It suggested that most of the mass was in the nucleus, the rest was empty space. He discovered this through his gold-foil experiment in which he shot radioactive particles through metal foils and detecting them using screens. Most passed through the foils, but some rebounded, causing his conclusion.
Citations: http://www.rsc.org/chemsoc/timeline/pages/1911.html

Niels Bohr

Aug 3, 1922

His theory was an extension of Rutherfords; and through a theory of observations and experiments it stated that electrons travel in specific orbits around the nucleus, that more outer orbits can hold more elctrons than the inner orbits and that these orbits determine the properties of an element.
-A problem with it is makes poor predictions regarding the spectra of larger atoms,
Citations: http://www.timetoast.com/timelines/64984
Picture: http://the-history-of-the-atom.wikispaces.com/Niels+Bohr

Electron Cloud Model

Mar 19, 1925

Erwin Schrödinger created this model, and it represents where the electron has been and where it is going. The red dot in the middle is the nucleus, while the red dots on the outside represent a trace of an electron. The many traces of electrons moving form a "cloud". The likely locations of the electron predicted by aerwin fit in with Bohr's location of the electrons specified by him
Citations & Picture: http://www.regentsprep.org/regents/physics/phys05/catomodel/cloud.htm

James Chadwick

Mar 19, 1932

Was the first to discover the neutron, it is named so because of its lack of electrical charge, which was previously an unknown particle in the atom. He also established the atomic number, which is the number of protons in the nuclues.
-There was not many if no problems with Chadawick's atomic theory. His work was correct and still stands today.
Citations: http://jameschadwickatomictheory.weebly.com/
Picture: Same as above