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Atomic Structure

What is Relative Atomic Mass?

Relative Atomic Mass can be written as RAM or A_r.

In a naturally occurring sample of Chlorine,
75% of the atoms will have a mass number of 35,
25% will have a mass number of 37.
The average mass number for the sample will be

[(75 x 35)  +  (25 x 37)] ÷100
= 35·5

The average mass number is called
the Relative Atomic Mass (RAM).
In this way, the relative atomic mass of any element can
be calculated, given the percentage of each isotope.

The mass number of any one atom will be a whole number.
The relative atomic mass is the average mass number
for all of the isotopes of that element.
The RAM is written in green
above each element in the periodic table.

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