Question

Guys please help tomorrow is my exam,, describe briefly and no google answers because I have already checked there..

Describe how the scattering of α-particles by thin metal foils provides evidence for the nuclear atom.

I will sure mark you the brainliest..

Answer 1

The experimental evidence behind the discovery involved the scattering of a particle beam after passing through a thin gold foil obstruction. The particles used for the experiment - alpha particles - are positive, dense, and can be emitted by a radioactive source.

Let us first recapitulate the background of the Rutherford experiments.

• The discovery of radioactivity, together with Thomson's proof of the independent existence of electron, provided a starting point for theories of atomic structure.
• The fact that atoms of a radioactive element are transformed into atoms of another element, by emitting positively and negativly charged particles led to the view that atoms are made of positive and negative charges.
• If this view is correct, the total negative charges in the atom must be an integral multiple of the electronic charge and since the atom is electrically neutral, under normal conditions, the positive and negative charges must be numerically equal.

• The emmision of electrons by atoms widely different conditions was a convincing evidence that electrons exist as such inside atoms.
• No particular assumptions could be made about the nature of the positive charges because the properties of the positive particles from radioactive substances and gas discharge tubes did not have the uniformity shown by the properties of the negative charges.
• Two questions arose. How many electrons are there in an atom? How are these electrons and positive charges arranged in an atom. X-ray studies revealed that the number of electrons per atom is of the of the order of the atomic weight. Further it was known that mass of an electron is about one two thousandth of the mass of a hydrogen atom , which has an atomic weight close to unity. From this it was logical to assume that practically the entire mass of the atom is associated with the positive charge.
• On this basis Thomson proposed a simple model. He assumed that the atom consisted of a sphere of positive charge of electricity of uniform density throughout which was distributed an equal and opposite charge in the form of electrons. Atom on this model was like a plum pudding with electrons distributed as currants in a dough of positive charge. The diameter of the sphere was taken as 10^-8 cm, the magnitude found for the atomic size.
• With this model we could calculate how atoms should behave under certain conditions and experiments done and results compared with predictions.
• One of the predictions was what would be mean deflection by a beam of alpha particles in passing through a thin gold foil and how the number of deflected particle would vary with angle of deflection.
• It was to test this prediction that scattering of alpha particles by thin gold foils was undertaken.
• At that time only natural radioactive sources were available, which gave alpha particles and beta particles.
• Alpha particles can be easily collimated to study scattering.

It was a fortunate coincidence that alpha particles scattering was studied as these interact much more than beta particles and would undergo Interactions which beta particles would not have.

Hope this may help you and be the brainliest

Happy learning !!

Answer 2

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A beam of a-particles was passed through the foil and some of the alpha particles (are positive) came out from different directions/ repelled. This meant that the positive charge in atoms was highly concentrated at one point for it to scatter the alpha particles. This shows that the atom had a positive nucleus with electrons outside the nucleus.