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The History Of The Atom Time Line

By Laura Casto, Coleen Beck, Alexis Russel, Lindsey Scruggs, and Vera Cole in 5th Period Chemistry

laura castro

on 19 October 2014

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Transcript of The History Of The Atom Time Line

384-322 BC
460- 370 BC

Chemistry Timeline
Aristotle was a Greek philosopher and scientist who openly rejected Democritus' atomic theory, which conflicted with his own ideas about nature.
Believed that empty space did not and could not exist.
Believed that all matter was comprised of either earth, fire, water or air.
Because of his influence, people followed his lead and rejected the Atomic Theory.

John Dalton
John Dalton was an English chemist, meteorologist, physicist and school teacher.
Came up with, through experimentation, Dalton's Atomic theory, which consisted of the following six main ideas.
Matter is composed of extremely small particles called atoms.
Atoms are indivisible and indestructible.
Atoms a given element are identical in size, mass and chemical properties.
Atoms of a specific element are different from those of another element.
Different atoms combine in simple, whole number ratios to form compounds.
In a chemical reaction, atoms are separated, combined or rearranged.
Robert A. Millikan (1869 - 1953)
The oil drop apparatus was created in 1909
He used a microscope and an oil apparatus to develop and support his model.
The major discovery that led to the development of this model was x - rays and discovering the charge of an electron.
For the Oil Drop Experiment: Millikan put a charge on a tiny drop of oil, and measured how strong an applied electric field had to be in order to stop the oil drop from falling through the hole in the apparatus. Since he was able to work out the mass of the oil drop, he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have. By varying the charge on different drops he noticed that the charge was always a multiple of -1.6 x 10-19C, the charge of a single electron. This meant that it was electrons carrying this charge.
The significance of the experiment was the quantity of a charge carried by an electron was constant for all electrons. The ultimate result of the experiment was the size of the charge on an electron and that the charge carried by an electron was a constant for all electrons.
Ernest Rutherford
James Chadwick
Discovered and proved the existence of the neutron through a series of complex mathematical equations.
discovered the neutron in 1932
he assumed the mass of the neutron to be close to that of the electron
In 1909 Ernest Rutherford performed the Geiger-Marsden experiment measuring deflection of alpha particles being passed through gold foil.
he expected there to be little to no deflection due to the spacing of the electrons.
the result of the experiment showed that there was something of a high charge in the gold foil causing higher degrees of deflection than had been expected.
constructed a new model of the atom different than what was previously thought
Democritus was a Greek, pre-Socratic philosopher who believed that matter was composed of tiny, unbreakable particles he called 'atomos', which moved through empty space.
The word atomos translates literally to 'uncuttable'. The term 'atom' is derived from Democritus' term.
Said that there were different atoms have different sizes and shapes.
Believed that the shape, size and movement of atoms were what determined the properties of matter.
Said that atoms are solid, homogeneous and indestructible.
Was met with much criticism when he could not answer the question, "What holds the atoms together?"
Joseph John (JJ) Thomson
JJ Thomson tried to prove that cathode rays carried a negative charge in the 1890's.
In one experiment he placed metal plates, one positively charged the other negatively charged on the tube. The rays were deflected by the negative plate and were attracted to the positive plate.
Thomson concluded that charges were bound to the rays, but also that the rays consisted of negatively charged particles.
He discovered electrons and received a Noble Prize in 1906 for this discovery.
Plum Pudding Model- an atom structure consisting of lots of electrons floating around in a positively charged background that balances the negative charged electrons. a uniform, positively charged sphere containing electrons.
His model displayed a positively charged nucleus surrounded by negatively charged electrons.
Alpha particle
John Dalton. (2014). The Biography.com website. Retrieved 05:11, Oct 16, 2014, from http://www.biography.com/people/john-dalton-9265201.
Dan Milx Ph.D. Paul Walorski. How did the Atom obtain its name. Retrieved from http://www.physlink.com/education/askexperts/ae622.cfm
Dan Milx Ph.D. Paul Walorski. How did the Atom obtain its name. Retrieved from http://www.physlink.com/education/askexperts/ae622.cfm
"Ernest Rutherford - Biographical". Nobelprize.org. Nobel Media AB 2014. Web. 16 Oct 2014. <http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html>
"James Chadwick - Biographical". Nobelprize.org. Nobel Media AB 2014. Web. 16 Oct 2014. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html>
"Discovery of the Neutron." Discovery of the Neutron. N.p., n.d. Web. 15 Oct. 2014. <http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrondis.html>.
"Alpha Particles." EPA. Environmental Protection Agency, 26 July 2012. Web. 17 Oct. 2014. <http://www.epa.gov/radiation/understand/alpha.html#properties>.
The Editors of Encyclopædia Britannica. "alpha particle (physics)." Encyclopedia Britannica Online. Encyclopedia Britannica, 14 July 2014. Web. 17 Oct. 2014. <http://www.britannica.com/EBchecked/topic/17152/alpha-particle>.
Niels Bohr
Geiger-Marsden experiment
Ernest Rutherford
Niels Bohr was a Noble prize winning physicist whose atomic structures help shape research worldwide.
Atom Model created from experiment's results
J.J. Thompson's previous model of the atom with expected results
Bohr came up with the revolutionary theory of an revolutionary theory on atomic structures and radiation emission.
Bohr's model of the atom was described as a small , positively charged nucleus surrounded by electrons that travel in a circular orbits around the nucleus.
Bohr's model is something called the planetary model because the fact that the elecetrons are arrranged in circular orbits around the nucleus of the atom, this resembling how the planets orbit the sun.
Palermo, Elizabeth. "Niels Bohr: Biography & Atomic Theory." LiveScience. TechMedia Network, 14 May 2013. Web. 14 Oct. 2014.
the neutron consists of two negatively charged d-quarks and one positively charged u-quark that cancel each others charges out (as shown in photograph on left)
James Chadwick

"Niels Bohr." Famous Scientists.N.p., n .p. wed. 16 Oct. 2014.
"Niels Bohr-Biographical ." Niels Bohr - Biographical. N.p., n.p. wed. 14 Oct. 2014.

Neutron model
His reason of why electrons orbit around the nucleus was depending on the energy state of the atom.
Dingrando, Laurel, Thandi Buthelezi, Nicholas Hainen, Cheryl Wistrom, and Dinah Zike. "Chapter 4 : The Structure of the Atom." Chemistry: Matter and Change. New York, N.Y.: Glencoe/McGraw-Hill, 2008. 100-133. Print.
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