daltons

Daltons, or daltons, refer to a non-SI unit of mass used to express atomic and molecular masses. The unit is named after the 19th-century English chemist John Dalton, who helped develop atomic theory. In scientific writing the symbol Da is standard, and the term is also encountered as “unified atomic mass unit” (u) in older literature.

Definition and equivalence: One dalton is defined as 1/12 of the mass of a carbon-12 atom, making it about 1.66053906660 × 10^-27 kilograms. It is also conveniently expressed as 1 gram per mole (1 g/mol). Consequently, a single atom or molecule with a mass of 1 Da weighs about 1.6605 × 10^-27 kg, and molecular masses are often quoted in Da or kilodaltons (kDa) for larger biomolecules.

Usage: The dalton is widely used to describe atomic, ionic, and molecular masses in chemistry, biochemistry, and molecular biology. In practice, many biomolecules are expressed in kilodaltons (kDa), for example a protein with a mass of 50 kDa. Small molecules such as glucose have masses on the order of a few hundred Da, while larger complexes can reach millions of Da. The unit provides a convenient scale for comparing masses without carrying large kilogram values.

Notes on notation: In formal contexts, Da is used for both singular and plural references (e.g., “2 Da”). When written in full, the plural form can be “daltons.” The dalton is synonymous with the unified atomic mass unit (u) and is related to the molar mass used in chemical calculations.