The Atom - pt. 3

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   16      atom      atom      electrons      elements      isotopes      isotopes      mass      mass      mass      neutron      neutron      neutron      neutrons      neutrons      neutrons      neutrons      nucleus      number      particle      protons      protons      protons   

The third important which is located in the nucleus is called the . It has a mass nearly equal to that of the proton - 1,840 times that of the electron. The has no electrical charge. You can see that the is one of the main factors in determining the of an atom. In any atom the atomic is equal to the number of plus the number of neutrons. For example, the oxygen contains 8 neutrons and 8 , so its atomic mass equals . Some have atoms with different numbers of in the . The chlorine atom, for example, has an atomic of 17 - there are 17 in the nucleus. The chlorine always contains the same number of protons. However, the number of in the chlorine atom is not always the same. Some chlorine atoms contain 18 neutrons, some contain 20 . Atoms with different numbers of are called . Most elements have isotopes, some of them having as many as 24. Since atoms of have the same number of protons and , they react the same chemically, even though their is different.