Parts of the periodic table

What do the numbers on the periodic table represent?
         Uper left numpber is the elements atomic number.  It is the number of protons.

         Upper right number is the elements atomic mass.

          Mg is the the chemical abbreviation for magnesium.

          The difference between Na and K elements.

          K is the name for Potassium.  It is in the period 4 on the periodic table.
          Na is the name for Sodium.  It is in the period 3 on the periodic table.
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