Editing Dalton (unit) (section)

=== 2019 revision of the SI ===
The definition of the dalton was not affected by the [[2019 revision of the SI]],<ref name=cipm106/><ref name=cgpm26/><ref name=bipm9th/> that is, 1&nbsp;Da in the SI is still {{sfrac|1|12}} of the mass of a carbon-12 atom, a quantity that must be determined experimentally in terms of SI units. However, the definition of a mole was changed to be the amount of substance consisting of exactly {{physconst|NA|unit=no|ref=no}} entities and the definition of the kilogram was changed as well. As a consequence, the [[molar mass constant]] remains close to but no longer exactly 1&nbsp;g/mol, meaning that the mass in grams of one mole of any substance remains nearly but no longer exactly numerically equal to its average molecular mass in daltons,<ref name=lehm2016/> although the relative standard uncertainty of {{val|4.5|e=-10}} at the time of the redefinition is insignificant for all practical purposes.<ref name="bipm9th" />  One entity, symbol ent, is the smallest amount of any substance (retaining its chemical properties). One mole is an aggregate of an Avogadro number of entities, 1 mol = ''N''<sub>0</sub> ent. This means that the appropriate atomic-scale unit for molar mass is dalton per entity, Da/ent = ''M''<sub>u</sub>, very nearly equal to 1 g/mol. For Da/ent to be exactly equal to g/mol, the dalton would need to be redefined exactly in terms of the (fixed-''h'') kilogram. Then, in addition to the identity g = (g/Da) Da, we would have the parallel relationship mol = (g/Da) ent = ''N''<sub>0</sub> ent, conforming to the original mole concept—that the Avogadro number is the gram-to-dalton mass unit ratio.