Question

Why are relative atomic masses on the periodic tables not whole numbers?

Answer 1

The sum of the number of protons and neutrons in an atom is called the mass number. Atomic mass is never an integer number for several reasons: The atomic mass reported on a periodic table is the weighted average of all the naturally occurring isotopes. Being an average it would be most unlikely to be a whole number.

Step-by-step explanation:

Answer 2

They are averages.

Step-by-step explanation:

atomic numbers on periodic tables are derived from the average value of all the isotopes of the element. So being averages they are sometimes not integers.