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Journey of Discovery of Atom

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Misra Ozel

on 8 December 2013

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Transcript of Journey of Discovery of Atom

Journey of Discovery of Atom
400 B.C
"by convention bitter, by convention sweet, but in reality atoms and void"
Democritus’ atomic theory posited that all matter is made up small indestructible units he called atoms.
He believed atoms were like billiard balls. Like Democritus.

All matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass, shape, size and other properties.

Two Chemical Laws

Conservation of Mass and Constant Proportions are explained on the base of Dalton’s theory.

Discovered that certain compounds dissolved in water contain charged particles. These charged particles conduct electricity. Coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis.
Faraday and Crook’s made several experiments and notice that there might be negatively charged particles in atom .

Stoney proposed that electricity was made of discrete negative particles he called "electrons ".

J. J. Thomson measured the ratio which is charge of electron =(1.76 / 108 coulombs/g) mass of electron.

He knew that the atom must have a positive component as well to balance the negatively charged particles, but he couldn’t find it.

He created the Plum Pudding Model of the atom which included electrons embedded in a positively charged cloud.

Studied radiations emitted from uranium and thorium and named them alpha and beta.
Ernest Rutherford and his friends (1911) made an experiment to test the J. J. Thomson’s atomic model.

Gold Foil Experiment: Rutherford shot alpha particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.

Thompson’s model could not be correct.
All of an atom’s positive charge, (as well as most of atom’s mass) is concentrated in a very small core at the atom’s center. Rutherford called this core
the nucleus.
Most of the volume of the atom is empty space.

Rutherford’s Conclusion
In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. He obtained more precise results in 1910 with his famous oil-drop experiment in which he replaced water with oil.Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron.

He first published his Law of Definite Proportions (or Law of Constant Composition) in 1794.
This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. For example, to make water there is a specific ratio of grams of hydrogen to grams of oxygen regardless of where your sample of water was found. All water has this particular proportion

Lavoisier was known for his experimentation skills. One of his favorite experiments being turing HgO into Hg+O. He used this experiment to help himself come up with the Law of Conservation. The law states that matter cannot be made or destroyed.
Chadwick discovered neutrons.They differed from alpha rays because they repelled considerable electrical forces that are in the nucleus of many heavy atoms. A neutron can then penetrate and split the nuclei of most elements.

Bohr studied the structure of an atom. He suggested that electrons didn't spiral into the nucleus, but orbit in different levels. This is called the bohr model, or the quantum model. The more energy an atom gives off, the closer it is to the nucleus, the more it absorbs, the farther away.
Modern Atomic

His contribution to the atomic theory was that he calculated the behavior of electrons, and subatomic particles that also make up an atom.
He contribute to Science in many ways he developed the wave mechanics approach to quantum theory , he also contributed to the Atomic theory originally more thought of by John Dalton.
De Broglie - 1926
His ideas were a basis for developing the wave mechanics theory.
atomictimeline. (2013, 11 19). Retrieved from atomictimeline: http://atomictimeline.net/index.php
barcodesinc. (2013, 11 15). Retrieved from barcodesinc: http://www.barcodesinc.com/articles/timeline-on-atomic-structure.htm
thehistoryofatom. (2013, 11 16). Retrieved from thehistoryofatom: http://the-history-of-the-atom.wikispaces.com/Louis+de+Broglie
timetoast. (2013, 11 19). Retrieved from timetoast: http://www.timetoast.com/timelines/60653
Chemistry Lesson Notes

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