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