The structure of atoms developed throughout time since 410 BCE to now. “Leucippus of Miletus (ca. 435 BCE) and Democritus of Abdera (ca. 410 BCE) developed the atomic hypothesis.” Their Theory was that the world is made up of atoms moving around in empty space, also in continuous motion and constantly colliding into each other. The ancient Greek philosophers were the first people to have the theory of atoms and no one continued their theory until early 1803 which was where John Dalton modernised the ancient Greek idea.
John Dalton’s theory was proposed giving a lecture at the Royal Institutions in 1803. The theory stated that “All matter is composed of atoms, Atoms cannot be made or destroyed, All atoms of the same element are identical, Different elements have different types of atoms, Chemical reactions occur when atoms are rearranged, Compounds are formed from atoms of the constituent elements.” Dalton’s theory provided other scientists to continue on with Dalton’s theory, which lead them into new areas of experiments.
In the late 1800’s JJ Thompson, the Physicist discovered the sub atomic particle known as the electron. JJ Thompson made a model known as the “Plum Pudding” where you can see the pudding as positive charged and the plums as negatively charged electrons. This theory was invalid due to what is known as the Rutherford gold foil experiment, which is designed to probe an atom.
Rutherford’s gold foil experiment displayed that the atom is mostly empty space, the nucleus is positively charged and the nucleus carries most of the atoms mass. “This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated with zinc sulfide (a scintillator).”
Neils Bohr in 1913 said when modelling the atom that electrons are in orbits around the nucleus various energy levels. For example, how the planets orbit around the sun.This led to possible calculations of possible energy levels for the orbitals. He also said that the emission of light occurs when an electron enters into an orbital which has lower energy levels.
References http://sciencenetlinks.com/lessons/history-atom-ancient-greeks/ http://www.rsc.org/chemsoc/timeline/pages/0450.html http://www.rsc.org/chemsoc/timeline/pages/1897.html http://www.universetoday.com/38326/plum-pudding-model/ http://www.rsc.org/chemsoc/timeline/pages/1911.html http://www.rsc.org/chemsoc/timeline/pages/1913.html http://www.rsc.org/chemsoc/timeline/pages/1926.html http://www.dummies.com/how-to/content/atomic-structure-the-bohr-model.html
References: http://sciencenetlinks.com/lessons/history-atom-ancient-greeks/ http://www.rsc.org/chemsoc/timeline/pages/0450.html http://www.rsc.org/chemsoc/timeline/pages/1897.html http://www.universetoday.com/38326/plum-pudding-model/ http://www.rsc.org/chemsoc/timeline/pages/1911.html http://www.rsc.org/chemsoc/timeline/pages/1913.html http://www.rsc.org/chemsoc/timeline/pages/1926.html http://www.dummies.com/how-to/content/atomic-structure-the-bohr-model.html
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