Atomic Mass

Atoms — and the protons, neutrons, and electrons that compose them — are extremely small. For example, a carbon atom weighs less than 2 × 10⁻²³ g. When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu). The amu was originally defined based on hydrog...

The mass of a single atom is very small, so it is not practical to measure the mass in grams or kilograms. The mass of atoms and molecules are measured in units called Daltons, abbreviated Da, or atomic mass units, abbreviated amu, or sometimes just u.

The mass of an atom in amu is approximately equal to the sum of the number of protons ...