Chemistry

What was Shown by Rutherfords Gold Foil Experiment



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Nobel Laureate Ernest Rutherford is known for being one of the first men to have split the atom.  This father of modern nuclear physics also discovered protons, theorized about the existence of neutrons, and revised science’s view on the structure of the atom.  All these things he accomplished with creativity and a piece of gold foil.

Ancient Views on the Atom

Around 400 B.C., Democritus of Abdera stated that all matter is made up of units that move around in a void. Democritus believed that these units are indivisible and unchangeable. These units he called atomos, which meant uncuttable in Greek.  It is also an idea with which Aristotle disagreed. Aristotle’s view, which prevailed through the Renaissance, was that all matter was made up of four basic elements ( fire, air, earth and water.)

Post Democritus

Centuries past before any new thoughts, regarding atoms and the make up of matter, took place.  But, in the 1700s, the law of Conservation of Mass was first presented by Antoine Lavoisier.  He revealed that relative to chemical reactions, the mass of the combined agents was the same as the mass of the result.  A contemporary of Lavoisier, Joseph Louis Proust divined the Law of Definite Proportions.  Under this law, Proust found proportions of the masses of elements composing a substance will always remain equal.

Teacher John Dalton was intrigued by the work of Lavoiser and Proust.   He often experimented with known elements oxygen, cooper, and carbon.  While working through chemical reactions, he confirmed Lavoisier and Proust’s findings.   Dalton’s experiments lead him to conclude several other things which were that all elements are made of up atoms, which are invisible particles that cannot be divided.  He also believed that atoms had relative mass and combined with other atoms to form compounds.

Dalton’s theory was revolutionary and did away with the old Aristotelian idea of four elements.   Dalton envisioned that the atom was like a blob of plum pudding. However, Dalton’s work did not explain some of the properties or reactions of atoms.  It would be almost another 100 years before the true nature of the atom would be revealed by Ernest Rutherford.

Subatomic World Revealed

In 1897, Sir. Joseph John Thomson studying cathode rays found the negatively charged particle found in atoms.  By the end of the 19th century, a capable chemist and physicist by the name of Ernest Rutherford had began work trying to decipher the phenomenon of radioactivity.  In 1909, working with Hans Geiger and Ernest Marsden, a special experiment was devised- the Gold Foil Experiment.

The Gold Foil Experiment

Sometimes referred to as the Rutherford or the Geiger Marsden Experiment,  this experiment was designed to explore the nature of the atom and the reaction of alpha particles.

As the experiment was set up, a beam of  alpha particles would be generated and beamed onto a thin sheet of gold foil.  The foil, surrounded by a sheet of zinc sulfide would light up as the alpha particles hit it.  Rutherford had used a similar experiment, using a vacuum  tube and photographic plate,  in  1906, and he observed that alpha particles seemed to scatter.

In 1909, the gold foil experiment was initiated.  Contained in a vacuum, Geiger and Marsden sent a beam of alpha particles on the thin piece of gold foil.  The scientists noticed that the particles passed easily in most cases, but in some cases the particles were deflected.  This deflection was rather unexpected and was contrary to the plum pudding view of the atom.

Rutherford’s Conclusions

From this experiment, Rutherford concluded that that majority of the mass of the atom must rest in a nucleus, which was positively charged.  He also gleaned that the atom has a positive charged particle, which he called a proton and it might have neutral particles in the core as well.  His views brought about a new atomic model called the planetary model.

While Rutherford’s theory did not wholly explain certain phenomena, he was on the right track.  His observations however did not explain the nature of electron orbits or reveal the neutron, although his observations postulated on the existence of an additional particle in the core of the atom.

Ernest Rutherford clearly was a giant in the field of physics.  He learned from the works of other innovators such as John Dalton and J.J. Thomson, and mentored many more, such as Nobel Laureates Niels Bohr and James Chadwick.  His innovative approach to science lead him to unravel a mystery that took men 2000 thousand years to solve, the structure of the atom.

There are a number of resources regarding Ernest Rutherford and his famous gold foil experiments.  You can find them at the local library or bookstore.  The web also provides several useful resources. Check out the following for more information:

 http://www.britannica.com/EBchecked/topic-art/41549/18080/The-Rutherford-gold-foil-experiment-In-1911-physicist-Ernest-Rutherford

http://www.ehow.com/about_4569065_rutherfords-gold-foil-experiment.html


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