The small unit of mass used to label the weight of atoms is the atomic mass unit (amu).

Here's why it's important:

* Atoms are incredibly tiny: Their masses are too small to express in grams or kilograms.

* Relative comparison: The amu allows us to easily compare the masses of different atoms. One amu is defined as 1/12th the mass of a carbon-12 atom.

* Convenient scale: Most atoms have atomic masses close to whole numbers, making it easy to work with.

For example, a hydrogen atom has an atomic mass of approximately 1 amu, while an oxygen atom has an atomic mass of approximately 16 amu.