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Rutherford's Gold Foil Experiment
Rutherford started his scientific career with much success in local schools leading to a scholarship to Nelson College. After achieving more academic honors at Nelson College, Rutherford moved on to Cambridge University's Cavendish laboratory. There he was lead by his mentor J.J. Thomson convinced him to study radiation. By 1889 Rutherford was ready to earn a living and sought a job. With Thomson's recommendation McGill University in Montreal accepted him as a professor of chemistry. Upon performing many experiments and finding new discoveries at McGill university, Rutherford was rewarded the nobel prize for chemistry. In 1907 he succeded Arthur Schuster at the University of Manchester. He began persuing alpha particles in 1908. With the help of Geiger he found the number of alpha particles emitted per second by a gram of radium. He was also able to confirm that alpha particles cause a faint but discrete flash when striking luminescent zinc sulfide screen. These great accomplishments are all overshadowed by Rutherford's famous Gold Foil experiment which revolutionized the atomic model.
This experiment was Rutherford's most notable achievement. It not only disproved Thomson's atomic model but also paved the way for such discoveries as the atomic bomb and nuclear power. The atomic model he concluded after the findings of his Gold Foil experiment have yet to be disproven. The following paragraphs will explain the significance of the Gold Foil Experiment as well as how the experiment contradicted Thomson's atomis model.
Rutherford began his experiment with the philosophy of trying "any dam fool experiment" on the chance it might work.1 With this in mind he set out to disprove the current atomic model. In 1909 he and his partner, Geiger, decided Ernest Marsden, a student of the University of Manchester, was ready for a real research project.2 This experiment's apparatus consisted of Polonium in a lead box emitting alpha particles towards a gold foil. The foil was surrounded by a luminescent zinc sulfide screen to detect where the alpha particles went after contacting the gold atoms. Because of Thomson's atomic model this experiment did not seem worthwhile for it predicted all the alpha particles would go straight through the foil. Despite however unlikely it may have seemed for the alpha particles to bounce off the gold atoms, they did. Leaving Rutherford to say, "It was almost as incredible as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you." Soon he came up with a new atomic model based on the results of this experiment. Nevertheless his findings and the new atomic model was mainly ignored by the scientific community at the time.
In spite of the views of other scientists, Rutherford's 1911 atomic model was backed by scientific proof of his Gold Foil Experiment. When he approched the experiment he respected and agreed with J.J. Thomson's, his friend and mentor, atomic theory. This theory proposed that the electrons where evenly distributed throughout an atom. Since an alpha paritcle is 8,000 times as heavy as an electron, one electron could not deflect an alpha particle at an obtuse angle. Applying Thomson's model, a passing particle could not hit more than one elctron at a time; therefore, all of the alpha particles should have passed straight through the gold foil. This was not the case - a notable few alpha particles reflected of the gold atoms back towards the polonium. Hence the mass of an atom must be condessed in consentrated core. Otherwise the mass of the alpha particles would be greated than any part of an atom they hit. As Rutherford put it:
"The alpha projectile changed course in a
single encounter with a target atom. But
for this to occur, the forces of electrical
repulsion had to be concentrated in a region
of 10-13cm whereas the atom was known to
measure 10-8cm."
He went on to say that this meant most of the atom was empty space with a small dense core. Rutherford pondered for much time before anouncing in 1911 that he had made a new atomic model-this one with a condensed core (which he named the "nucleus") and electrons orbitting this core. As stated earlier, this new atomic model was not opposed but originally ignored by most of the scientific community.
Rutherford's experiment shows how scientists must never just accept the current theroies and models but rather they must constently be put to new tests and experiments. Rutherford was truly one of the most successful scientists of his time and yet his most renowned experiment was done expecting no profound results. Currently, chemists are still realizing the uses for atomic energy thanks to early findings from scientists such as Rutherford.