Rutherford's model of an atom :. Ernest Rutherford was interested in knowing how the electrons are arranged within an atom. Rutherford designed an experiment for this.
From the data he also calculated that the radius of the nucleus is about 10 5 times less than the radius of the atom. On the basis of his experiment, Rutherford put forward the model of an atom, which had the following features:. Rutherford's alpha particle scattering experiment shows the presence of nucleus in the atom. It also gives the following important information about the nucleus of an atom:. Rutherford found that a small percentage of alpha particles were deflected at large angles, which could be explained by an atom with a very small, dense, positively-charged nucleus at its center bottom.
Surprisingly, while most of the alpha particles were indeed undeflected, a very small percentage about 1 in particles bounced off the gold foil at very large angles. Some were even redirected back toward the source. No prior knowledge had prepared them for this discovery. Rutherford needed to come up with an entirely new model of the atom in order to explain his results.
Because the vast majority of the alpha particles had passed through the gold, he reasoned that most of the atom was empty space. In contrast, the particles that were highly deflected must have experienced a tremendously powerful force within the atom. The nucleus is the tiny, dense, central core of the atom and is composed of protons and neutrons.
In the nuclear atom, the protons and neutrons, which comprise nearly all of the mass of the atom, are located in the nucleus at the center of the atom. The electrons are distributed around the nucleus and occupy most of the volume of the atom. It is worth emphasizing just how small the nucleus is compared to the rest of the atom. If we could blow up an atom to be the size of a large professional football stadium, the nucleus would be about the size of a marble.
However, it did not completely address the nature of the electrons and the way in which they occupied the vast space around the nucleus. It was not until some years later that a full understanding of the electron was achieved. But can discovery be the same for a realm hidden from sight? One cannot see an atom in that sense. So this hints that perhaps the story of the discovery of the nucleus was more complicated. The story as it unfolded in Rutherford's lab at the University in Manchester revolved around real people.
It involved frustrations and triumphs. It involved hard work and perplexity and inspiration. Rutherford arrived in Manchester in the summer of , months before the university's term began. He had been named Langworthy Professor of Physics, successor to Arthur Schuster — , who retired at age 56 to recruit Rutherford. Schuster had built a modern physics building, hired Hans Geiger, Ph. Rutherford entered the center of the physics world. Researchers came to him by the dozen. I found Rutherford's place very busy, hard working.
But a very dirty place. Namely, Manchester is very foggy, foggy and smoky. And of course everywhere you see smoke there, everywhere the smoke. You have to build it yourself of cocoa boxes, gold leaf and sulfur isolation.
And you charge the electroscope by sealing wax which you rubbed on your trousers. So it was a very primitive technique. But of course also a microscope to read the electroscope. Now the microscope was fixed and then you were not supposed to touch it.
And of course you were not supposed to clean it. So years went on without apparatus being cleaned. But apart from the shortcomings it was a very fine lab, nice rooms, and lots of people working there—able people I remember Moseley very well, with whom I was on very friendly terms.
I will tell you later about his work. And Charles Darwin was there. He was lecturing in theoretical physics. And Russell, who later came to Oxford. An Italian, Rossi, did spectroscopic work. He showed that ionium and sodium have the same spectrum. And then Geiger was there. He was an assistant. And also an assistant named Makower, who died since. Geiger and Makower published a book together. And also a chap Robinson, who worked on beta rays.
Gray, a New Zealand man. Marsden who came from Australia. Fajans who came from Germany. And Boltwood was there for a while. He came from Yale. Rutherford invited him in hope that Boltwood, a great chemist, would purify ionium, but he failed as many others. Rutherford arrived with many research questions in mind. He was not done with the puzzles of the decay families of thorium, radium, etc. Boltwood and Hahn both worked with Rutherford in Manchester, Boltwood in — and Hahn in — That is, he was leaving radio-chemistry to others and turning to physics.
Rutherford's early team at Manchester included Geiger and William Kay — , junior laboratory assistant since Rutherford promoted Kay to laboratory steward in , to manage lab equipment and to aid him in his research. In , Kay thought back to his youth with Rutherford in an interview. The language is quaint, but the description is as close to Rutherford's approach as we get.
The questioner was Samuel Devons — , who was one of Rutherford's last students in the s. We used to, I used to set up nearly all his apparatus. You know, when he did his work, you know, oftener than not, he used to tell me and we did a rough experiment, re It gives you And then we would do a rough experiment, and get one or two curves you see, and then straight away button it on to somebody else to do the real work, and that's how he did his They observed these through a microscope and counted the scintillations at different angles of dispersion.
The instrument, which evolved into the "Geiger counter," had a partially evacuated metal cylinder with a wire down its center. They applied a voltage between the cylinder and the wire high enough almost to spark.
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