In 1911, ernest rutherford and his assistants geiger and marsden conducted an experiment in which they scattered alpha particles (nuclei of helium atoms) from thin sheets of gold. an alpha particle, having charge +2e and mass 6.64 ✕ 10−27 kg, is a product of certain radioactive decays. the results of the experiment led rutherford to the idea that most of an atom's mass is in a very small nucleus, with electrons in orbit around it. assume an alpha particle, initially very far from a stationary gold nucleus, is fired with a velocity of 2.70 107 m/s directly toward the nucleus (charge +79e). what is the smallest distance between the alpha particle and the nucleus before the alpha particle reverses direction? assume the gold nucleus remains stationary.

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -

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