-
450
Democritus (460 B.C.)
Democritus suggested that matter was made of hard, small particles that couldn't be separated. He called these particles atomos, or atoms. He also said that atoms entirely fill up the space they are in. However, Democritus offered no factual evidence to support this claim, and it was not believed by many. Only 2000 years in the future would be the beginning of the modern atomic theory. -
450
Aristotle (350 B.C.)
Aristotle belived in the four elements of air, earth, water, and fire. He thought that regardless of the number of times you break something in half, you would always have a smaller piece, and there was no end. Despite having no evidence, his opinion was accepted for the next 2000 years. -
John Dalton
John Dalton was the man responsible for the atomic theory, which stated that matter is made of small, undividable particles called atoms. He also said that all atoms in the same element are exactly the same but are unalike from atoms of different elements. He used laws that were already made to support his findings, such as The Law of Conervation of Mass. He also conducted experiments using different chemicals and found that matter consists of "lumpy particles" which are atoms. -
Thomson (1897, 1904)
in 1897, he discovered electrons. In 1904, he said that atoms have a large body with a positive charge with negative parts spread throughout. He conducted experiments with cathode ray tubes that showed 'cathode rays' were always identical regardless of the nature the electrodes or gas use, and the 'canal rays' were different when different gases were used. His model was called "Plum Pudding." -
Rutherford
Rutherford's work spanned from 1911 when he tried bombarding atoms with alpha rays (so he could look inside atoms) to 1919 when he discovered protons. In 1911 He performed the "Gold Foil Experiment." Between those times, in 1912, he discovered the atomic nucleus. The way he discovered protons was interesting. He extracted the nucleus of Hydrogen out of atoms of six elements; boron, fluorine, sodium, aluminum, phosphorus, and nitrogen. -
Bohr
Bohr suggested that electrons move around the nucleus in set orbits, such as the planets around the sun. He also stated that an electron can move to a higher orbit (excited electrons) and those excited electrons can fall back to their original orbit. In order to support he discoveries, he used various tests. The Lyman Series went with excited electrons regressing to the lowest energy level. The Balmer Series went with excited electrons moving from higher energy levels to the 1st excited level. -
Heisenberg and Schrodinger (1925-1926)
Schrodinger's idea was: "Why not go all the way with particle waves and try to form a model of the atom on that basis?" Hersenberg's theory was called Matrix Mechanics which explained the behavior of atoms. The two theories were seemingly completely different, yet both worked. In their experiments, Shrodinger used the famous Two-Slit Experiment; and Heinsenberg used mathematical quantites he called matrices. -
Bibliographies Cont.
"HISTORICAL OUTLINE of the Atomic Theory and the Structure of the Atom." HISTORICAL OUTLINE of the Atomic Theory and the Structure of the Atom. N.p., n.d. Web. 25 Feb. 2014.http://cstlcsm.semo.edu/mcgowan/ch181/atomhist.htm.
"History of Atoms." History of Atoms. N.p., n.d. Web. 24 Feb. 2014. http://nobeliefs.com/atom.htm. -
Bibliographies
"Atom History." Atom History. N.p., n.d. Web. 26 Feb. 2014. http://molaire1.perso.sfr.fr/e_histoire.html.
"A Brief History of Modern Atomic Theory." Chemistry Tutorial : History of Atomic Theory. N.p., n.d. Web. 26 Feb. 2014. http://ausetute.com.au/atomichist.html.
"Chemistry Project : The History Of The Atom." Chemistry Project : The History Of The Atom. N.p., n.d. Web. 26 Feb. 2014. http://hi.fi.tripod.com/timeline/.
