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8.2   FROM THE UNIVERSE TO THE ATOM

        THE NUCLEUS

P82 004

In January 1913, J. J. Thomson reported the discovery of two types of neon atoms with relative masses 20 and 22.

 (A)

What name is given to these two types of atoms?

(B)

The average relative atomic mass of neon is 20.2. Calculate the proportions of the two types of atoms in a sample of neon.

 

 

 

View solution below only after you have completed answering the question. The solution is not in a form that you would answer in an examination. The answers are often in more detail to help improve your appreciation and understanding of the physics.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Solution

(A)

The two types of atoms are called isotopes.

Atomic number for neon is Z = 10.  The two isotopes are  20Ne10  (10 protons and 10 neutrons) and  22Ne10  (10 protons and 12 neutrons).

(B)

Let N1 be the percentage of the abundance of the atoms with relative mass equal to 20 and N2 be the percentage for atoms with relative mass 22. Then

             

            

             

           

               

 

             20Ne10  (90%)   and   22Ne10   (10%)