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manogyana25
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According to JJ Thomson's atomic model, Rutherford expected deflections of alpha particles through small angles. I'm unable to understand why he had expected "small angles". Can someone please explain.
Yes, it was understood that alpha particles were in fact helium nuclei. Rutherford himself had done experiments which proved such:jfizzix said:Before the Rutherford experiments, it was very popular to believe that an atom consisted of dot-like electrons suspended in a spread out positively charged cloud like a plum pudding (this being known as the plum pudding model of the atom).
If that were the case, then the alpha particles would mostly pass through or get deflected by small angles, because the only hard objects to scatter off of would be the tiny (and relatively light) electrons, which were much lighter than the alpha particles.
Since some of the alpha particles were actually deflected at large angles, the model of the atom was revised to be a small positively charged nucleus surrounded by orbiting negatively charged electrons.
Interesting side question:
At the time that those experiments were done, did scientists understand alpha particles to be charged nuclei of helium, or were they just thought of as different particles all their own?
Also:
Where'd the plum pudding model come from in the first place?
manogyana25 said:According to JJ Thomson's atomic model, Rutherford expected deflections of alpha particles through small angles. I'm unable to understand why he had expected "small angles". Can someone please explain.
Nugatory said:One of Rutherford's contemporaries (I do not remember who) remarked that the large angles were like firing a naval gun at a sheet of paper and having the shell sometimes bounce back instead of going through; that's not something that you'd expect. (My favorite image is to consider how surprised we'd be to find that a one-ton elephant is actually an elephant-sized cloud of elephant-colored weightless vapor surrounding a one-ton mosquito).
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. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre, carrying a charge.
SteamKing said:It was Rutherford himself who made this quote, in a lecture delivered at Cambridge U:
manogyana25 said:According to JJ Thomson's atomic model, Rutherford expected deflections of alpha particles through small angles. I'm unable to understand why he had expected "small angles". Can someone please explain.
Rutherford's Alpha particles experiment was a groundbreaking experiment conducted by scientist Ernest Rutherford in 1909. It involved directing a beam of alpha particles at a thin gold foil and observing their behavior.
Rutherford's experiment showed that most of the alpha particles passed straight through the gold foil, but a small percentage were deflected at large angles and a few even bounced straight back. This led to the discovery of the atomic nucleus and the concept of the atom having a small, dense, positively charged center.
Rutherford's experiment was important because it provided evidence for the existence of the atomic nucleus and helped to disprove the previously accepted "plum pudding" model of the atom. It also laid the foundation for further research and understanding of atomic structure.
Alpha particles are a type of radiation that consist of two protons and two neutrons, making them positively charged. They were chosen for the experiment because of their high energy and ability to penetrate materials, allowing for the observation of their behavior as they passed through the gold foil.
Rutherford's experiment revolutionized our understanding of the atom by showing that it consisted of a small, dense, positively charged nucleus surrounded by mostly empty space. This helped to explain the behavior of alpha particles and other subatomic particles and paved the way for further discoveries in the field of atomic physics.