In particular, reaction rates are very slightly affected by atomic mass.

As any artificial element, a standard atomic mass cannot be given.

The atomic masses of these isotopes range from 112 to 151.

Each atom in the sample has a "particular" atomic mass.

For other similar sounding terms, such as relative atomic mass, see the article on that subject.

However, because oxygen-17 and oxygen-18 are also present in natural oxygen this led to 2 different tables of atomic mass.

In so doing he corrected Berzelius's value for the atomic mass.

The same argument could be made against "relative atomic mass" used in this sense.

For example, the atomic mass of copper is about 63.55.

Thus, you can imagine that the average atomic mass of N is skewed very close to 14.