# =What particular isotope is the basis for defining the atomic mass unit and the mole?

The ""^12C isotope..........
$\text{Avogadro's number}$, $6.022 \times {10}^{23}$ individual ""^12C atoms have a mass of $12.0 \cdot g$ precisely. Given that we know the relative atomic masses of the other elements with respect to carbon, we can define the atomic masses of every other element.
The $\text{mole}$ is thus the link between the macro world of grams, and kilograms, and litres, to the micro world of atoms, and molecules. This idea of chemical equivalence is very important, and if you learn anything in chemistry, learn this principle at the very least.