Talk:Atomic weight

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Describe the new page here.

Can someone go through the Atomic Weight and Molarity pages and explain what is the parenthetical number that follows the listed atomic weights? Thanks! —Preceding unsigned comment added by (talk) 18:12, 2 January 2010 (UTC)

I think a typo has crept in - atomic weight is about the mass of an atom (not just the nucleus) and the reference is scale is that which an atom (not nucleus) of Carbon-12 is 12 units.

You should also make it clear that the 'average' is a weighted average over naturally occuring isotopes.

Perhaps I should have been bolder and simply editted the page but it is my first time here.

Kenneth Evans 3 February 2002

Atomic mass[edit]

I propose that this definition be moved to be primarily "Relative Atomic Mass" with "Atomic mass" and "Atomic weight" as redirects to that. It is the more correct term, and therefore should have the title really. At the moment statements like "atomic the mass" do not even make a great deal of sense, and really are contradictory.

Any strong disagreement? Thought the change was major enough to ask views first...

I can not see any reason why not, while I can see many reasons why. I say go ahead with it.
I proposed it on the changes page and people disagreed saying that it should reflect current usage, and that RAM was not current usage (it is current everywhere I've been, and among physicists is certainly standard, but possibly not among chemists, they are known to be terminologically lazy I'm told). Hence I've not changed it yet.

This page is a mess! I basically agree with the above posts. Why are we still insisting on the archaic term atomic weight? Totally inconsistent to use weight with units of grams. I've been teaching chemistry for 20 years and only refer to atomic weight in a historical context. Current usage is atomic mass. I have revived the atomic mass page - still needs work. Comments? -Vsmith 02:24, 3 Nov 2004 (UTC)

  • Atomic weight should now be a redirect... which I'll go do now. Eric119 02:31, 6 Dec 2004 (UTC)

Atomic weight is entirely inappropriate, and I fully support the move. Weight is mass*acceleration, but this article talks about masses. This must be changed. Adacus12 (talk) 08:04, 19 June 2010 (UTC)

You are replying to a rather old discussion thread - the article has likely changed a bit in 5.5 yrs. Historical context and IUPAC seem to be of importance here. Although I agree with your concerns about weight/mass, it seems others don't -- and please keep the article usage consistent with the title. If you want a rename or move of the article - then seek consensus for that here first. Vsmith (talk) 11:14, 19 June 2010 (UTC)

May I point out that atomic weight is a dimensionless unit (i.e. it is not measured in grams), it is molar mass that is somewhat like that, however in reality, that should be molar density, as it is mass per unit unit amount, or g/mol. It is not the mass, nor the weight that is used as a unit, so if you object to atomic weight, you should also object to atomic mass, or relative atomic mass. If you were to put a carbon 12 atom in any gravitational field, it will have an atomic weight of 12. Having it called mass is no better. Weight is proportional to mass (in the same gravitational field). As it is just a measure relative to carbon 12, weight is just as accurate as mass. Furthermore, as it is a weighted mean, it makes more sense for weight to be used. Black.jeff (talk) 08:29, 24 August 2011 (UTC)


Shouldn't atomic mass units be mentioned since that is what 1/12 of C-12 is? —Preceding unsigned comment added by (talk) 08:42, 16 April 2010 (UTC)

Depends! Atomic weight in chemistry has always been a dimensionless quantity, because it is measured as a ratio of masses. Physics tends to be more interested in the masses of individual nuclides, and there it makes very little difference if you quote the result as a mass in amu or as a dimensionless relative mass. So to say that the atomic weight of chlorine is 35.5 u is wrong (there is no chlorine atom which has a mass of 35.5 u), but to say that the atomic masses of the two stable isotopes of chlorine are approximately 35 u and 37 u is correct. Physchim62 (talk) 10:28, 16 April 2010 (UTC)


E.g. think that molar mass of water comes from mass of the hydrogen and the mass of oxygen. So kg/mol + kg/mol = kg/mol (1+ 1+ 16 or 0,001 + 0,001 +0,016 -> 0,018 kg/mol) Ooops. These quantities must be additive! The original meaning of atomic mass is forgotten? A agree that the title of the artice will be Relative atomic mass. The mass is not weight (after 1903 CGPM) ZJ (talk) 20:15, 15 October 2010 (UTC)