The Atomic Theory

By Keith McCabe

Democritus

Creator of the Atomic theory in

460 BC

DemocritusDemocritus was born in Abdera Greece, and lived past the age of 90.

During which time he developed many scientific theories, the most famous of which is the Atomic Theory, created in 460 BC. A theory based upon his teacher’s, Leucippus’, beliefs about matter, and states that the every object in the world are made up of little particles that he named atoma. These atomas, or atoms are infinite in number and imperceptible because they are too small to be seen by the human eye. Democritus went on to state that atoms move around empty space in objects and the combining of these different physically shaped atoms create the objects themselves. Atoms themselves were the only exemption from the last principle because Democritus believed them to be smallest form of matter and therefore solid. Lastly, the theory stated that atoms have always been and always will be, and no new atoms could every be made. In our time Democritus’ Atoma Theory is known as the beginning step in an important theory(even if most of it was wrong), however it wasn’t always seen in this light. It was once black listed by some of the centuries most influential philosophers, including Pluto, because it provided no merit to society.

John Dalton

Father of the atomic theory.

John DaltonThe Next Step in the history of the atom was John Dalton’s creation of a table

of elements and their atoms, represented by symbols, and his proposal of his Atomic Theory to the Royal Institution, both of which happened in 1803. Dalton’s proposed 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, and compounds are formed from atoms of the constituent elements. When theses ideas of atoms are combined they rationalized the laws of chemical combination that were unaccounted for. Although, he did make some mistakes in his theory including, the ideas that the simplest compound of two elements is binary, and formed from atoms of different elements in a 1:1 ratio. Another mistake in his theory was the inaccuracy of his atomic weighing system. For example, Dalton gave Carbon atoms a weight of 7 instead of 8. Dalton represented all of this data in a table of 21 elements and their atoms arranged by atomic mass and identified through 36 different symbols.

Dmitri Mendeleev

Creator of the Periodic Table

in 1869

Dmitri Mendeleev

Mendeleev as an independent scientist of chemistry created the Periodic Table in 1869. The table itself arranged elements by increasing atomic weight in vertical rows in way that the horizontal rows contain analogous elements, which was also arranged by increasing atomic weight. This easy to understand and well organized table made arriving at general conclusions and access to information quick and easy.

Eugene Goldstein

Discover of Protons in 1885

Eugene Goldstein

In 1885 Eugene Goldstein discovered that cathode-ray tubes filled with punctured cathodes produce a glow at the bottom of the tube near the cathode. Goldstein then rationalized that in addition to the cathode rays, (later discovered to be electrons) there must be another ray(which he names the canal ray) that travels from the positively charge conductor to the negatively charged conductor. This ray is later determined to be Protons.

Henri Becquerel

Henri Becquerel discovered natural Radioactivity in

1896.

Henri Becquerel In 1896 Henri Becquerel discovered Natural Radioactivity. The events leading

up this discovery are best described here, “Following a discussion with Henri Poincaré on the radiation which had recently been discovered by Röntgen (X-rays) and which was accompanied by a type of phosphorescence in the vacuum tube, Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer, caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903, the other half being given to Pierre and Marie Curie for their study of the Becquerel radiation.”http://www.nobelprize.org/nobel_prizes/physics/laureates/1903/becquerel-bio.html

J.J. Thomson

The man who discovered electrons in 1897

J.J. Thomson

During 1897 J.J. Thomson was investigating electricity with experiments inside of empty glass tubes in hope of solving the Cathode Rays mystery. His experiments ultimately lead to the discovery that Cathode rays are streams of negative particles smaller than atoms themselves! Now known as Electrons.

Ernest Rutherford

Discover of the Nucleus in 1907

Ernest Rutherford

Ernest Rutherford was the man who discovered the Nucleus of the atom by conducted his famed gold foil experiment. An experiment, in which, he shot a laser through gold foil and discovered that a small amount of light didn’t make it through, but instead bounced back. Thus, proving the existence of a nucleus for the first time, a fact that lead him to create a new model of the atom called the Billiard Ball Model.

Millikan

Proved Electrons have a negative charge in 1910.

Millikan

Millikan successfully proved that electrons have a negative charge in 1910. He did this using the falling-drop method of experimentation.

Frederick Soddy

Named Isotopes in 1913

Frederick Soddy

Frederick Soddy realized that many elements appeared to occupy the same space on the periodic table, which was very problematic. In order to fix this Soddy proposed the idea of isotopes, in which, atoms with the same protons, but a different number of neutrons were the same element, and merely what he then termed isotopes of each other.

Neils Bohr

Created the most widely accepted model of an atom in 1913.

Neils Bohr

One of the most monumental steps in the Atomic Theory was in 1913 when Neils Bohr created the Bohr model on an atom. The model depicted the nucleus as the center of an atom, with protons inside of it, and several layers of electrons which gravitated around the nucleus. After the discovery of Neutrons by Chadwick in 1932, Neutrons were add to the Bohr model and It became the model that is still used to teach the Atomic Theory in school today.

Heisenberg

Creator of Quantum mechanics 1925.

Heisenberg Heinsenberg created a new form of quantum mechanics to be used with atoms in1925. “Heisenberg set himself the task of finding the new quantummechanics upon returning to Göttingen from Copenhagen in April 1925. Inspired byBohr and his assistant, H.A. Kramers, in Copenhagen, Pauli in Hamburg, and Born inGöttingen, Heisenberg's intensive struggle over the following months to achieve hisgoal has been well documented by historians. Since the electron orbits in atoms couldnot be observed, Heisenberg tried to develop a quantum mechanics without them. Herelied instead on what can be observed, namely the light emitted and absorbed by theatoms. By July 1925 Heisenberg had an answer, but the mathematics was so unfamiliarthat he was not sure if it made any sense. Heisenberg handed a paper on thederivation to his mentor, Max Born, before leaving on a month-long lecture trip toHolland and England and a camping trip to Scandinavia with his youth-movementgroup. After puzzling over the derivation, Born finally recognized that the unfamiliarmathematics was related to the mathematics of arrays of numbers known as[matrices.] Born sent Heisenberg's paper off for publication. It was the breakthroughto quantum mechanics.”http://www.aip.org/history/heisenberg/p07.htm

Chadwick

Discovered Neutrons in 1932

Chadwick

Chadwick discovered neutrons, a previously unaccounted for particle in the nucleus of the atom. This Neutrons were discovered to have no charge and could therefore coulomb barrier and split the heaviest of atoms. A fact crucial to later studies of Nuclear reactions.

Photo Citations(In order of appearance in PowerPoint)

• wp-blogs.moundsparkacademy.org• http://www.livius.org/de-dh/democritus/democritus.html• probertencyclopaedia.com• http://www.chemistry.co.nz/mendeleev.htm• http://reich-chemistry.wikispaces.com/422-003+Big+Time+Line+Project+ANDREW+

M.+AND+KEVIN+D.+BIG+TIME+LINE

• http://www.accessexcellence.org/AE/AEC/CC/historical_background.php• http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html• http://www.juliantrubin.com/bigten/millikanoildrop.html• http://sosscienceclub.wordpress.com/• http://www.splung.com/content/sid/5/page/matter• http://

www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html• http://en.wikipedia.org/wiki/James_Chadwick