Practice Problem 1

Determine the number of protons, neutrons, and electrons in a 210Pb2+ ion.


The atomic number of lead is 82, which means this ion contains 82 protons.  Since it has a charge of +2 , this ion must contain 80 electrons.  Because neutrons and protons both have a mass of about 1 amu, the difference between the mass number (210) and the atomic number (82) is equal to the number of neutrons in the nucleus of the atom.   The ion therefore contains 128 neutrons.

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