# Question about the definition of an isotopes

My answer was as follows : atoms of the same element with differrnt relative atomic masses.

However in the mark scheme the answer was simply : atoms of the same element with different masses.

Was there something wrong with my answer?

Why does it matter?

Usually the term "relative atomic mass" for an element is a weighted average of the atomic masses of the various isotopes of an element, with the weighting determined by their abundance. So, since the atomic masses of various isotopes enter into this determination, your first answer is not too good.

• İ still don't understand. :( Sep 9 '18 at 20:08
• en.wikipedia.org/wiki/Relative_atomic_mass#Current_definition
– Karl
Sep 9 '18 at 20:25
• the term "relative atomic mass" already implies a mixture of isotopes, so you can't use that term for the atomic mass of a single isotope Sep 9 '18 at 20:26
• So the relative atomic mass is not the mass the mass of a single isotope then ? Sep 9 '18 at 21:21
• yes $\phantom{}$ Sep 9 '18 at 21:25

You would only use “relative atomic mass” to describe the mass number you see on the periodic table, which is essentially the average mass of all the isotopes of that element, proportional to their abundances.

Isotopes are atoms of an element which have the same number of protons but differing numbers of neutrons, and therefore, different masses.