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Word Count: 467
The nucleus has more than 100 protons and more than 150 neutons the nucleus is a very small part of an atom Both the atom and the necleus can be thought of as spheres Then both volumes of the atom can be compared with the volume of the nucleus alone because the volume of a sphere is proportional to the cube of its radius The space outside the nucleus is occupied only by electrons The observation has led to the empty space concept of matter Ernest Rutherford a British physicist performed an experiment that strongly suggested that the positive charge of an atom located in a very small nucleus Rutherforths experiment made use of polonium a radioactive element that gives of positvely charged particles These particles are called alpha particles A steam of these particles was allowed to strike a thin sheet gold or copper Behind the metal foil was a fluorescent screen This diagram showes what Ernest Ruthefold and his colleges observed Most of the alpha particles passed through the metal foil with very little interference Each time one of the alpha particles hit the flourescent screen a flash of light was given offFew particles did not pass though the foil Rutherford found that a very few alpha particles was deflected by more than 90 Because of these experiments he made a nuclear model of the atom which described the atom with its nucleus and an atoms lack of energy charge An atom is electrically neutal because it has negatively charged particlesor electronsthat balance the positive charge of the nucleus The electrons are present in the empty space surrounding the nucleus The atomis number is the number of positive charges in the nucleus of an atom Each proton carries one positve charge The atomic number represents the number of protons in the nucleus of an atom The atomic number never changes The mass of an
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