Final answer:
Atomic masses are measured in atomic mass units (amu), which are based on a value of exactly one-twelfth the mass of a carbon-12 atom.
Step-by-step explanation:
Atomic masses are measured in atomic mass units (amu) or simply u, which is a relative unit based on a value of exactly one-twelfth the mass of an atom of carbon-12 (12C). The atomic mass unit is extremely useful for comparing the masses of different atoms and molecules because their absolute masses are very small and not practical for comparison using grams. For example, the mass of helium-4 is 4.0026 amu, and the mass of sulfur-32 is 31.972 amu. The atomic mass of an element is calculated as a weighted average of the masses of all its naturally occurring isotopes.
Furthermore, 1 amu is equivalent to 1.660539 × 10-24 grams. This scale allows an easy comparison of masses between different atoms and subatomic particles, with protons and neutrons having an approximate mass of 1 amu each, facilitating the calculation of atomic masses. For precise measurements, such as the exact mass of uranium-238 being 238.050788 u, scientific references provide more exact values.