Element X has 17 protons, 17 electrons, atomic number 17, representing chlorine with electronic configuration 2, 8, 7 and seven valence electrons. Adding two neutrons raises mass number to 37, forming its isotope.
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In a neutral atom, protons equal electrons, so there are 31 protons. Subtracting 31 protons from the mass number 70 gives 39 neutrons present in the nucleus of atom X.
Rutherford concluded that the positive charge is not spread out but concentrated at the center in an extremely small, dense region called the nucleus, which also contains nearly all the mass of the atom.