THE ATOM! ERNEST RUTHERFORD BY Saxon de Araujo

Assignment 4 Ernest Rutherford Ernest Rutherford conducted a famous experiment called the gold foil experiment. He took a thin sheet of gold foil. He used special equipment to shoot alpha particles (Positively charged particles) at the gold foil. Most particles passed straight through the foil like the foil was not there. Some particles went straight back or were deflected (went in another direction) as if they had hit something. 1. How did he know that atom was mostly empty space? 2. What happened to the alpha particles as they hit the gold foil? 3. How did he know that the nucleus was positively charged? 4. Describe Rutherford's gold foil experiment and how the results changed the model of the atom. Ernest Rutherford Ernest Rutherford conducted a famous experiment called the gold foil experiment. He took a thin sheet of gold foil. He used special equipment to shoot alpha particles (Positively charged particles) at the gold foil. Most particles passed straight through the foil like the foil was not there. Some particles went straight back or were deflected (went in another direction) as if they had hit something. 1. How did he know that atom was mostly empty space? 2. What happened to the alpha particles as they hit the gold foil? 3. How did he know that the nucleus was positively charged? 4. Describe Rutherford's gold foil experiment and how the results changed the model of the atom.

He figured out that the atom is mostly empty space because they passed through the gold foil sheet. He knew that it wasn’t all empty space because some of them bounced back. HOW DID ERNEST RUTHERFORD KNOW THAT THE ATOM WAS MOSTLY EMPTY SPACE?

What happened to the alpha particles as they hit the gold foil? Although many of the alpha particles did pass through as expected, many others were deflected at small angles while others were reflected back to the alpha source. A very small percentage of particles were deflected through angles much larger than 90 degrees. According to Rutherford: It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15- inch shell at a piece of tissue paper and it came back and hit you.

Describe Ernest Rutherford's gold foil experiment and how the results changed the model of the atom. Rutherford's experiment consisted of a beam of alpha particles, generated by the radioactive decay of radium, directed normally onto a sheet of very thin gold foil in an evacuated chamber. A zinc sulfide screen at the focus of a microscope was used as a detector; the screen and microscope could be swiveled around the foil to observe particles deflected at any given angle. Under the prevailing plum pudding model, the alpha particles should all have been deflected by, at most, a few degrees; measuring the pattern of scattered particles was expected to provide information about the distribution of charge within the atom. According to Rutherford: “On consideration, I realized that this scattering backward must be the result of a single collision,….It was then that I had the idea of an atom with a minute massive centre, carrying a charge.”

How did he know that the nucleus was positively charged? The fact that some of the alpha particles were deflected or reflected meant that the atom had a concentrated centre of positive charge and of relatively large mass. The alpha particles had either hit the positive centre directly or passed by it close enough to be affected by its positive charge. Since many other particles passed through the gold foil, the positive centre would have to be a relatively small size compared to the rest of the atom - meaning that the atom is mostly open space. Because most of the positive particles continued on their original path unmoved, Rutherford concluded that most of the remainder of the atom was a region of very low density. A great deal of charge was also associated with the central region of high density. Rutherford hypothesized that these two properties resided in the same physical structure and termed his discovery "the central charge", a region later named the nucleus.

Thus the current view of the nuclear atom - a structure with a positively charged centre (nucleus) of high density and negatively charged electron particles moving around the nucleus at relatively large distances compared to the nuclear radius - was created. Rutherford was able to say from the experiment that the nuclear charge was positive and used the following language for pictorial purposes: "For concreteness, consider the passage of a high speed Alpha particle through an atom having a positive central charge Ne, and surrounded by a compensating charge of N electrons."

Ernest Rutherford facts Ernest Rutherford was a New Zealand chemist who helped pioneer nuclear physics. He won a Nobel Prize in chemistry, made numerous contributions to science and worked closely with a number of his students who went on to make their own significant discoveries. Ernest Rutherford lived from the 30th of August 1871 to the 19th of October Rutherford studied at Canterbury College, University of New Zealand before moving to England in 1895 for post graduate study at Cavendish Laboratory, University of Cambridge. Rutherford worked on radioactivity, coining the terms ‘alpha’ and ‘beta’ to describe the two different types of radiation emitted by uranium and thorium.

He also observed that radioactive material took the same amount of time for half of it to decay, known as its “half life”. In 1907, Rutherford, Hans Geiger and Ernest Marsden carried out the Geiger-Marsden experiment, an attempt to examine the structure of the atom. The surprising results of this experiment demonstrated the existence of the atomic nucleus and became an integral part of the Rutherford model of the atom. The Rutherford model of the atom was simplified in a well known symbol showing electrons circling around the nucleus like planets orbiting the sun. This symbol became popular and has been used by various organizations around the world as a symbol for atoms and atomic energy in general. In 1908, Rutherford was awarded the Nobel Prize in Chemistry for his work on the transmutation of elements and the chemistry of radioactive material. The element 'rutherfordium' was named in Rutherford’s honor.

“If you can't explain your physics to a barmaid it is probably not very good physics.” “All science is either physics or stamp collecting.” “Radioactivity is shown to be accompanied by chemical changes in which new types of matter are being continually produced..... The conclusion is drawn that these chemical changes must be sub- atomic in character.” Famous Ernest Rutherford quotes include:

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