Rutherford's Atomic Model
In 1910, Ernest Rutherford, a new zelander physics, wanted to prove the atomic model proposed by Sir Joseph Thomson. The experiment he made to do this consisted in passing an alpha particles ray (positively charged particles) through a extremely thin piece of gold paper. This is shown, in a very simple way, in Image 4. The results got from this experiment, take to Rutherford to postulate a new atomic model, which appear in Image 5. The main conclusions that were obtained from the experiment were:
- Atom has a lot of space inside it, which could explain why ost of the particles went through the gold paper with no deviation from their path.
- Atom has a dense center, which gives the mass of the atom. This center, called nucleus, is positively charged, too. This could explain why the alpha particles suffered deviation from their path when they approach to a nucleus.
- Due to the atom is a electrically neutral particle, the electrons must be around the nucleus, going round it in orbits like planets do around the Sun. The number of electrons is equal (but with opposite sign) to the charge present in the nucleus.
Well, now, why the raisin cake model was invalid to explains these results? The answer is: The Thomson's model considered the atom as a compact sphere, which has the electrons set into it. If this model would have been the right one, the alpha particles should have bounced against the gold paper, because it's the same when two balls hit each other. But, the most part of the particle went through te paper, so it means that the Thomson's atomic model was wrong.
Image 4: Gold paper experiment
Image 4: Gold paper experiment
Eugen Goldstein, in 1886,discovered that it was possible to see rays running from the cathode to the anode (in a cathode ray tube), if some holes were made on the latest, everything occuring while a electric current is applied. He discovered that these rays (which he called channel rays) were positively charged and their mass was dependent of the gas inside the tube. These charges were named protons. But, these particles have the same sign between them, so they should repel each other, but they are putting together in the nucleus, so Rutherford thought that another particle must exist, which could act as a "glue" between protons and could get the nucleus's stability.
When the 30's started, James Chadwick, a Rutherford's student, discovered the prescence of a non-charged particle, which had roughly the same mass as a proton. Thos unknown particle was called neutron, corroborating the Rutherford's theory about the existance of that particle.