atomimassayksiköinä

Atomimassayksiköinä, often abbreviated as amu, is a unit of mass used to express the mass of atoms and molecules. It is defined as one-twelfth of the mass of an unbound neutral atom of carbon-12 in its ground state. The symbol for the atomic mass unit is u. This unit is particularly useful in chemistry and physics for expressing the masses of subatomic particles and the masses of isotopes. It is also known as the unified atomic mass unit.

The value of one atomic mass unit is approximately 1.66053906660 × 10^-27 kilograms. This precise value is derived from experimental measurements and is fundamental to many calculations in nuclear physics and chemistry. The concept of the atomic mass unit arose from the need for a consistent and convenient scale for atomic masses, rather than using absolute mass values which are extremely small. The carbon-12 standard was adopted in 1961. Before this, there were slightly different scales based on oxygen.