Dalton (unit)

Jean Perrin 1926

Johann Josef Loschmidt portrait plaque

Silicon-unit-cell-labelled-3D-balls

Dalton (unit) is a unit of mass used to express the mass of atoms, molecules, and other particles. It is equivalent to the unified atomic mass unit (u) and is denoted as Da. The Dalton is named after John Dalton, a British chemist and physicist who is known for formulating the atomic theory and for his research in the chemistry of atmospheric gases. The use of the Dalton as a unit of mass helps in simplifying the representation of molecular masses, which are often very small and expressed in terms of grams per mole at the macroscopic scale.

Definition

One Dalton is defined as 1/12th of the mass of a free neutral atom of carbon-12 (12C), at rest and in its ground state. This definition ties the Dalton directly to the kilogram, as the carbon-12 atom has a mass of exactly 12 Da, making it a convenient standard for expressing atomic and molecular masses. The exact value of one Dalton is approximately 1.660539040 × 10^-27 kilograms.

Usage

The Dalton is widely used in chemistry, biochemistry, and physics to express the masses of atoms and molecules. In biochemistry, for example, the sizes of proteins and other large biomolecules are often stated in kilodaltons (kDa), where 1 kDa equals 1000 Da. This unit provides a clear and concise way to communicate very small masses that would otherwise require cumbersome scientific notation if expressed in grams.

Advantages

One of the main advantages of using the Dalton is its direct relation to the atomic mass unit, making it ideal for use in the sciences where atomic and molecular masses are frequently discussed. It simplifies calculations and communication about particle masses, as it allows scientists to easily compare the masses of different molecules and atoms without converting into grams or other units of mass.

History

The concept of the atomic mass unit was developed in the early 19th century, with John Dalton's atomic theory. Dalton's work laid the foundation for modern chemistry by demonstrating that matter is composed of atoms of different weights, which combine in simple ratios to form compounds. The unit named in his honor, the Dalton, was later adopted to provide a standard measurement for atomic and molecular masses, facilitating greater precision and uniformity in scientific research.

See Also

• Atomic mass unit
• Molecular mass
• John Dalton
• Atomic theory
• Biochemistry
• Chemistry

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