NUCLEAR & PARTICLE PHYSICS
THE NUCLEUS
23. PERIODIC PROPERTIES
Atomic number Z(the number of protons) and mass number A (the number of
nucleons). The number of neutrons is N=A-Z. All nuclei having same A and
Z are said to be the same nuclide; nuclides with identical Z are called
isotopes. The symbol for a nucleus of Z protons and A-Z neutrons is , where
the X is the chemical symbol of the element. (The Z is really redundant
here, because the element's symbol tells you how many protons it has. Nevertheless,
sometimes it's hard to remember the Z for Rubidium, or Platinum, or what-have-you,
so I will include it.)
Examples: Carbon has 6 protons and therefore 6 electrons. The energy levels
of the electrons determine its chemical behavior, not its nucleus. The
number of neutrons can vary: 98.89% of carbon has 6 neutrons (is or C-12)
but 1.11% has 7 neutrons (i.e. ). For Uranium the percentages are 99.27%
, 0.72% , and 0.0057% .
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