Ernest Rutherford: The Geiger-Marsden Experiment
Ernest Rutherford is the man behind the discovery of the central charge in a nucleus. This significant finding changed scientists view on atoms The discovery of the nucleus is one of, if not the most important to have ever been made. In this essay I will be discussing how previous assumptions of the atom's shape, curiosity and an accident led to Rutherford's discovery of the proton. Data and equations from his original journal will also be discussed to further prove the presence of a central charge.
Before the discovery of the nucleus, scientists accepted The Plum Pudding Model proposed by J. J Thomson. In this theory of the atom it was thought to have negative charged electrons surrounded by positively charged matter. Both the positive matter and negative electrons were in equal amounts leading to a neutral atom. It was named the Plum Pudding Model because it was visualised as a pudding, where the raisin symbolised the electrons and the pudding represented positive matter.
Ernest …show more content…
Rutherford was first interested in alpha particles and how they would scatter and effect matter when they hit a thin sheet of mica. What's interesting is that he did not set out to prove The Plum Pudding Model wrong .His original thought was that the alpha particles would all pass through the thin sheet . This can be seen in figure 2. However, to his surprise it did not happen. This is what got Rutherford to question the Plum Pudding Model. If it was correct then there would be no diversion of alpha particles. As a scientist he questioned everything and this was a great inquisition for the response changed how we think of atoms, the building blocks of life.
To answer his question, Rutherford constructed an experiment called The Gold Foil Experiment which is also known as the The Geiger-Marsden Experiment.
Rutherford did not conduct the experiment but supervised and explained the observations, it was done by Hans Geiger and Ernest Marsden. The gold foil experiment consisted of an apparatus that emitted alpha particles which we now know to be helium nuclei, a gold foil which was 0.00004cm thick and a detector which was a zinc sulphide screen that detected that alpha particles once it passed the gold foil. Alpha particles were used because they were positively charged, extremely dense and travelled at a high speed. To count the particles Geiger and Marsden would sit in the dark for thirty minutes to an hour so their eyes would adjust. Then they would count the alpha particles that were hitting the zinc sulphide screen using a microscope. They would switch turns every thirty minutes so they could be as precise and accurate as
possible.
The results of the investigation showed that most of the alpha particles went through, however 1 out of 20,000 alpha particles would turn at around 90 degree angle as seen in figure 1. Rutherford said it was “As if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you”(Rutherford,1911). It was unexpected because an alpha particle is positive and if the Plum Pudding Model was correct and atoms are surrounded by negatively charged corpuscles then it would be presumed that the alpha particles would have went straight through. The science behind the Plum Pudding Model was that, as the alpha particle approached the atom repulsion between the atom and the alpha particle would increase. This would happen because the alpha particles are positively charged and the atom was thought to be surrounded by a positive “pudding” . Also the electrons would be too small to have an effect. Once the alpha particle reached the cloud force of the atom, the force would decrease because the particle invaded the atom's energy space. This should have only caused a slight change in the alpha particles pathway and not a complete diversion. The only explanation for such great deflections to occur, even if it is only of a few alpha particles was that the region where the alpha particle was hitting the atom must have been small, positively charged and due to a single strong encounter. So it caused a deflection of the alpha particle with maximum force. Also Rutherford mentioned that the deflection was due to a central charge and not the other constituents of the atom. In his original work Rutherford said for such deflection to occur an atoms mass is concentrated in the centre and also said that this centre is almost 1000 times smaller than the atom as a whole.
Before the discovery of the nucleus, scientists accepted The Plum Pudding Model proposed by J. J Thomson. In this theory of the atom it was thought to have negative charged electrons surrounded by positively charged matter. Both the positive matter and negative electrons were in equal amounts leading to a neutral atom. It was named the Plum Pudding Model because it was visualised as a pudding, where the raisin symbolised the electrons and the pudding represented positive matter.
Ernest …show more content…
Rutherford was first interested in alpha particles and how they would scatter and effect matter when they hit a thin sheet of mica. What's interesting is that he did not set out to prove The Plum Pudding Model wrong .His original thought was that the alpha particles would all pass through the thin sheet . This can be seen in figure 2. However, to his surprise it did not happen. This is what got Rutherford to question the Plum Pudding Model. If it was correct then there would be no diversion of alpha particles. As a scientist he questioned everything and this was a great inquisition for the response changed how we think of atoms, the building blocks of life.
To answer his question, Rutherford constructed an experiment called The Gold Foil Experiment which is also known as the The Geiger-Marsden Experiment.
Rutherford did not conduct the experiment but supervised and explained the observations, it was done by Hans Geiger and Ernest Marsden. The gold foil experiment consisted of an apparatus that emitted alpha particles which we now know to be helium nuclei, a gold foil which was 0.00004cm thick and a detector which was a zinc sulphide screen that detected that alpha particles once it passed the gold foil. Alpha particles were used because they were positively charged, extremely dense and travelled at a high speed. To count the particles Geiger and Marsden would sit in the dark for thirty minutes to an hour so their eyes would adjust. Then they would count the alpha particles that were hitting the zinc sulphide screen using a microscope. They would switch turns every thirty minutes so they could be as precise and accurate as
possible.
The results of the investigation showed that most of the alpha particles went through, however 1 out of 20,000 alpha particles would turn at around 90 degree angle as seen in figure 1. Rutherford said it was “As if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you”(Rutherford,1911). It was unexpected because an alpha particle is positive and if the Plum Pudding Model was correct and atoms are surrounded by negatively charged corpuscles then it would be presumed that the alpha particles would have went straight through. The science behind the Plum Pudding Model was that, as the alpha particle approached the atom repulsion between the atom and the alpha particle would increase. This would happen because the alpha particles are positively charged and the atom was thought to be surrounded by a positive “pudding” . Also the electrons would be too small to have an effect. Once the alpha particle reached the cloud force of the atom, the force would decrease because the particle invaded the atom's energy space. This should have only caused a slight change in the alpha particles pathway and not a complete diversion. The only explanation for such great deflections to occur, even if it is only of a few alpha particles was that the region where the alpha particle was hitting the atom must have been small, positively charged and due to a single strong encounter. So it caused a deflection of the alpha particle with maximum force. Also Rutherford mentioned that the deflection was due to a central charge and not the other constituents of the atom. In his original work Rutherford said for such deflection to occur an atoms mass is concentrated in the centre and also said that this centre is almost 1000 times smaller than the atom as a whole.