> Even for this SI overhaul, we didn't really even need to redefine the mole, except for the fact that it was previously defined in terms of the old kg. This was just "fixing a glitch".
I came to complain about the article calling the mole a "base unit of the SI", and this seems like an appropriate thread.
Why is the mole a defined unit at all? As far as I understand things, "one mole" is the same thing as Avogadro's number -- neither can be a unit, because they're both dimensionless constants (well, they're both one and the same dimensionless constant). Applying actual units, "one mole of water molecules" is the same thing as "Avogadro's number of water molecules". Avogadro's number, and therefore the mole, is the conversion factor between atomic mass units and grams. Similarly, 3 is the conversion factor between feet and yards, but nobody thinks 3 is a fundamental base unit of the imperial system. The foot is a base unit of the imperial system, measuring length, the yard is a non-base unit also measuring length, and 3 is a number with no special relationship to the system at all. It would be total nonsense to say that yards are defined by reference to 3. How is Avogadro's number different?
Wouldn't "fixing the glitch" be abandoning the idea of calling the mole a unit in the first place?
I'm pretty sure the mole is not defined as 6 * 10^23 mol^{-1}.
There is a concept of "the Avogadro constant", which is defined to have units of mol^{-1} (at least, according to a cited statement on wikipedia), but that is not a coherent concept -- since mol is dimensionless, mol^{-1} is also dimensionless.
> Since its adoption into the International System of Units in 1971, numerous criticisms of the concept of the mole as a unit like the metre or the second have arisen:
> the number of molecules, etc. in a given amount of material is a fixed dimensionless quantity
> the mole is not a true metric (i.e. measuring) unit
> One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.
amu and g are both units of mass, so 1 amu = 1 g/mol is an explicit statement that mol is dimensionless.
Calling mol a unit won't accomplish anything except corrupting your dimensional analysis. mol is not analogous to the SI units meter, second, ampere, gram, kelvin, etc. -- it is analogous to the SI prefixes kilo-, mega-, milli-, micro-, nano-, etc.
I came to complain about the article calling the mole a "base unit of the SI", and this seems like an appropriate thread.
Why is the mole a defined unit at all? As far as I understand things, "one mole" is the same thing as Avogadro's number -- neither can be a unit, because they're both dimensionless constants (well, they're both one and the same dimensionless constant). Applying actual units, "one mole of water molecules" is the same thing as "Avogadro's number of water molecules". Avogadro's number, and therefore the mole, is the conversion factor between atomic mass units and grams. Similarly, 3 is the conversion factor between feet and yards, but nobody thinks 3 is a fundamental base unit of the imperial system. The foot is a base unit of the imperial system, measuring length, the yard is a non-base unit also measuring length, and 3 is a number with no special relationship to the system at all. It would be total nonsense to say that yards are defined by reference to 3. How is Avogadro's number different?
Wouldn't "fixing the glitch" be abandoning the idea of calling the mole a unit in the first place?