... the foil almost undeflected. However Geiger and Marsden found that, although most of them did this, some bounced back. Picture This gave a new picture of the atom with a small positively charged nucleus containing almost all the mass, surrounded by empty space through which the alpha particle had passed. Occasionally an alpha particle had passed so close to the nucleus that it was repelled backwards. The electrons must be found surrounding the nucleus to balance out the positive charge. The Proton Rutherford went on to prove that protons are the positive particles found in the nucleus of all atoms, and that their positive charge is the same magnitude as the negative charge on the electron. The number of protons is the proton number, which is, of course a fundamental property of the element. The Neutron This was discovered in 1932 and was found to be in the nucleus having the same mass as ...

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