-
450
Democritus (460 BC)
Democritus developed the idea of atoms. He thought at some point you couldn't get any smaller. Another thing was that differentatoms make different shapes, like hooks for iron and spikes for salt
His method to this was that when you keep cutting something in half you will eventually hit a point that you can't cut anymore.
He didn't know what the atom actually looked like.
Walker, Jim. "History of Atoms." History of Atoms. N.p., Sept. 1988. Web. 27 Feb. 2014. http://www.nobeliefs.com/atom.htm. -
450
Aristotle (about 2500 years ago)
Aristotle believed the idea of atoms was worhtless. He thought there were no atoms. He believed different things are made up of different things: Earth, water, air, and fire.
To prove this he used scientic facts.
He didn't know what it looked like because he didn't think there was an atom.
. -
John Dalton
Dalton believed that matter is composed of tiny invisible particles called atoms. He also believed that all atoms of one element are identical but are different from the atoms of other elements. He also said chemical reactions consitst of rearranging atoms in simple whole number ratios. He used evidence from the Law of Mass Conservation by Lavoisier in 1789, the Law of Constant Composition by Praust in 1799, and the Law of Multiple Proportions by Dalton himself. -
Dalton, continued
Dalton believed that atoms looked like indivisible balls of matter. -
J.J. Thompson's Plum Pudding Model
Thompson suggested that, unlike Dalton's model, atoms are divisable and consist of a sphere of positively charged embedded with tiny negatively charged particles, which made the atom neutral. When experimenting with cathode tubes, Thompson observed that positive charges were different when different gases were used and that negative charges were identical regardless of gas or electrode. He thought that an atom resembled plum pudding. -
Ernest Rutherford
Earnest Rutherford discovered that instead of the positve charge being spread out with electrons embedded randomly (as in the Plum Pudding Model), the positive charge is focused in hte center of an atom. In essence he discovered the nucleus of the atom, which were made of protons. He believed that electrons orbited the nucleus. Later, he discovered that the nucleus consisted positvely charged protons and neutral neutrons. -
Rutherford continued
Rutherford discovery is supported by the Gold Foil experiment which he conducted on 1909. He was actually trying to prove the Plum Pudding model. He shot alpha particles (now understood to be Helium atoms), which had a +2 charge,at a sheet of gold foil. The foil was surrounded by a detector. If the Plum Pudding model was correct, then the alpha particles should have shot through the foil with minimal deflection. This however, was not the case. Some of the particles were deflected. -
Bohr
Bohr discovered that the electrons moved around a fixed nucleus. He thought that an electron could absorb energy; another thing he believed was that an excited electron can fall back to its original orbit by emmiting energy as radiation. The other thing he believed was that electrons only exist in certain energy levels.
The method that Bohr used to make his discovery was that when an excited electron falls back to the lowest energy level known as the ground state. -
Bohr (continued)
Bohr thought that an atom had a nucleus and electrons orbitted around the nucleus on certain paths. -
Heisenburg and Schrodinger
The combined efforts of Werner Heisenberg and
Erwin Rudolf Josef Alexander Schrödinger contributed the quantum physics as well as the Principle of Indeterminancy. The Principle of Interdeminance states that you cannot know the position and velocity of an electron at the same time. Quantum physics states that an electron is a particle yet it is also a wave. They exist in several energy levels surrounding the nucleus of an atom in an electron cloud. From them we have the most current atom model -
All citations
History of the Atom Timeline. Dir. Tyler Dewitt. Perf. Tyler DeWitt. YouTube, 2012. YouTube.
Walker, Jim. "History of Atoms." History of Atoms. N.p., Sept. 1988. Web. 27 Feb. 2014.http://www.nobeliefs.com/atom.htm.
"A Brief History of Modern Atomic Theory." Chemistry Tutorial : History of Atomic Theory. Ausetute, n.d. Web. 27 Feb. 2014. <http://www.ausetute.com.au/atomichist.ht
"Atomic Structure Timeline." Atomic Structure Timeline. N.p., 2004. Web. 27 Feb. 2014. http://atomictimeline.net/. -
All citations (continued)
"University of Colorado Boulder." University of Colorado Boulder. N.p., n.d. Web. 27 Feb. 2014. http://www.colorado.edu/. All sources were used for each person
