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What is a relative atomic mass of an element?

Answer Text:
Introduction to relative atomic masses and isotopes:
- The masses of individual atoms of elements are very negligible and thus quite difficult to weigh.
- On average the mass of an atom is approximately #10^-22#g which cannot be determined by an
ordinary laboratory balance.
- For this reason the mass of atom has been expressed relative to that of a chosen standard element
hence the term relative atomic mass.
- The initial reference element was hydrogen which was later replaced with oxygen.
- Later the oxygen scale was found unsuitable;
Reason:
Oxygen exists I several isotopes and thus led to problems when deciding the mass of an oxygen atom.
- For this reason oxygen was replaced with carbon as the reference atom and to date relative atomic
masses of elements are based on an atom of carbon-12 (note that carbon is isotopic and exists as
Carbon -12 or carbon-14).
Definition:
Relative atomic mass (R.A.M) of an element refers to the average mass of an atom of the element compared with a twelfth (1/12) of an atom of carbon-12.