Tuesday, October 5, 2010

Gold Foil Experiment

Rutherford's Gold Foil Experiment
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The gold foil experiment (aka Geiger-Marsden experiment) was created by Hans Geiger and Earnest Marsden under Ernest Rutherford in 1911 to explain the structure of an atom. The researchers used the laboratory at the University of Manchester to prove the plum pudding model. However, their surprising results disproved the theory and led to the creation of the Rutherford model.(4) 
Ernest Rutherford(8)
Ernest Rutherford is called the "father of nuclear physics." He won the Nobel Prize in chemistry in 1908 for working with radioactive substances but is most famous for revising the model of the atom. His gold foil experiment disproved the plum pudding model proposed by J.J. Thomson, Rutherford's former professor.(7)
above: plum pudding model
below: gold foil experiment
The plum pudding model was created in 1904 by J.J. Thomson, a physicits who discovered the electron with a cathode ray tube in 1897. He believed that the negatively charged electrons were embedded in a sphere or cloud positively charged matter.(5)
The Experiment
Rutherford's experiment(9)
Rutherford, Geiger, and Marsden shot alpha particles (positively charged particles) at a gold foil surrounded by fluorescent screen. According to Thomson's plum pudding model, positive and negative charges were distributed evenly within the atom. Because of this model, Rutherford and his colleagues believed that most of the alpha particles would pass through the gold foil. To their surprise, a small percent of of the particles were deflected at various angles.(6) 
The Results
alpha particles(6)
Because the alpha particles were impacted at very high velocities and large angles, it had to be hitting an extremely dense center. Rutherford concluded that the dense center held most of the atom's mass and consisted of protons and neutrons while the electrons orbited the nucleus. This explained why most of the alpha particles passed the empty space that the electrons circled and a small percent of particles reflected when they hit the nucleus.
Rutherford's model
The Rutherford Model
Rutherford created a new model of the atom with the positively charged nucleus, containing protons and neutrons, as the center and negatively charged electrons orbiting the nucleus.(6) He believed that the centripetal force of the revolving electrons was generated by from the electrostatic force of attraction between the nucleus and electrons.(10)
Flaws in Rutherford's Theory
1) Because of the electromagnetic waves theory, the electrons orbiting the nucleus could not have centripetal force without becoming unstable.
2) Despite what Rutherford believed, the atoms could not radiate a constant spectrum of electromagnetic waves.
The Importance
From their experiment, Rutherford and his colleagues discovered the nucleus of an atom. The results of the gold foil experiment replaced the plum pudding model with a more accurate model of an atom. The Rutherford model gives a representation of how protons, neutrons, and electrons are arranged in an atom. 

Works Cited