Are atomic mass and atomic weight the same thing?

Jan 15, 2016

No, they are not the same thing.

Explanation:

An atomic weight (or relative atomic mass) is the ratio of the average mass of all the isotopes of an element to $\frac{1}{12}$ of the mass of an atom of $\text{^12"C}$.

Hence an atomic weight has no dimensions.

Atomic mass is the mass of a neutral atom of a specific isotope.

The SI unit for atomic mass is the unified atomic mass unit (u), which is defined as $\frac{1}{12}$ of the mass of an atom of $\text{^12"C}$.

Thus, the atomic weight of $\text{C}$ is 12.011, but the atomic mass of $\text{^12"C}$ is 12 u.