Non-SI unit accepted for use with SI
|Name||Symbol||Quantity||Value in SI units|
|dalton||Da||mass||1.660 539 040 (20) × 10−27 kg
1.660 539 040 (20) yg
The dalton, symbol Da, or unified atomic mass unit, is a non-SI unit of mass accepted for use with the SI.
One dalton is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest.
In SI units, one dalton is 1.660 539 040 (20) × 10−27 kg, or approximately 1.66 yoctograms.
The dalton is used as a unit of mass for quantities on an atomic or molecular scale. One dalton is approximately the mass of one nucleon (either a single proton or neutron), and is approximately equivalent to 1 g mol-1.
Examples of atomic and molecular masses
|Name||Symbol/formula||Mass in Da||Mass in SI units|
|carbon dioxide||CO2||44.01||73.08 yg|
|human haemoglobin||≈ 64 000||≈ 106 000 yg|
Prior to 2019, the mole was defined in terms of the kilogram and the dalton, and was equal to
“the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12”.
The numerical value of the mole is now defined exactly, and the value of the dalton in SI units must be obtained experimentally.