dalton

This term is used exclusively within the specialized registers of chemistry, physics, and molecular biology. It provides a convenient scale for discussing the mass of single atoms or molecules without resorting to the extremely small values of kilograms or grams.

As a standard unit of measurement for atomic mass, it is treated as an uncountable entity in the context of the unit's definition, though it is used as a countable noun when specifying a quantity of mass (e.g., 18 daltons).