Gram atomic mass -- what exactly is it?

[Hamiltonian]

TL;DR

Is gram atomic mass, atomic mass(of an element) represented in grams, or the mass of one mole of an element

It is stated that the gram atomic mass of an element is its atomic mass represented in grams. The gram atomic mass of sodium is said to be 23g (isn't this number way to big to represent the mass of an atom?!) but if its the mass of one mole of sodium it makes sense(but won't that be molar mass). I searched it up and I kept seeing both definitions used interchangeably so I am not too sure which is correct.

 

[Borek]

Yes, there is a lot of lousy wording, but units are selected in such a way that exactly the same number depicts mass of one mole of element expressed in grams and mass of one atom of that element expressed in a.m.u.

(actually for most elements there is no such thing as a well defined 'atom of the element', as they are mixtures of isotopes)

 

[Hamiltonian]

Yes, there is a lot of lousy wording, but units are selected in such a way that exactly the same number depicts mass of one mole of element expressed in grams and mass of one atom of that element expressed in a.m.u.

(actually for most elements there is no such thing as a well defined 'atom of the element', as they are mixtures of isotopes)

so the magnitude of the atomic mass unit of an element is always equal to the mass of one mole of that element in grams?

 

[Borek]

Yes, that's why a.m.u. has such a random value, it is just 1g/N_A.

 

[Hamiltonian]

Yes, that's why a.m.u. has such a random value, it is just 1g/N_A.

Isn't the a.m.u of an element given relative to the C-12 isotope which is assigned 12 a.m.u hence the value of $1a.m.u = 1.66*10^{-27}$Kg

 

[Borek]

Actually it is a bit like asking what was first - an egg, or a hen? Both approaches are equivalent and both produce the same result - molar mass in grams and atomic mass in amu are the same number. The definition was chosen as the primary just for clarity, not because it is more fundamental than the other approach.

 

[mjc123]

"Gram-atom" is an old-fashioned term for what we call a mole. It is equal to the relative atomic mass in grams (relative to H = 1 in the old days, I suppose) - not the mass of one atom. So 1 gram-atom of sodium is 23 g - the same as 1 mole. So the gram atomic mass is the same thing as the molar mass.