Talk:Atomic mass unit
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[edit] Dalton as a size unit
In biology, the Dalton is often used in this way: "Only proteins smaller than [...]KDa can pass through this channel/pore." Since it is a unit of mass, isn't this strange? Are mass and size correlated in proteins? Since proteins can fold in many different ways, I would think that some proteins of a certain mass would and others would not fit through a channel/pore. Anyone?
Why did they choose the AMU convention of 1/12 of C12 rather than the origional standard with 1/16 016?
- Probably in large part because that was only the convention of chemists, not physicists who used 1/16 of the naturally occuring mixture of oxygen (or maybe it was vice versa). That's where the first word in the officially recognized name of this unit comes from: unified atomic mass unit, with the symbol u, is the only way this is recognized as "acceptable for use with SI". Gene Nygaard 21:01, 23 September 2005 (UTC)
How come only biological sciences use the Dalton unit? In chemistry there is rarely a unit. The header in a table of molecular weights would be labelled 'mw' or 'molecular weight' with no unit. Just a guess, but it may be because, when talking about large molecular weights, 'kilo (no unit)' sounds kind of stupid.
How do you change Atonic mass into pounds?
- via Kilograms.
I removed the following paragraph; I think it's overly simplistic and illustrates a principle of college algebra rather than of atomic masses. It is certainly not relevant to the amu unit. It also uses the term "relative atomic mass" in a strange way and. AxelBoldt 16:44, 9 Oct 2004 (UTC)
[edit] Using Mass Spectrum Data to Calculate Relative Atomic Mass
A simple calculation may be used to calculate the relative atomic mass of the sample. This is demonstrated in the following example.
| Ion | Relative Mass | Percentage Abundance |
| 11C+ | 11 | 70% |
| 13C+ | 13 | 30% |
Therefore, the relative atomic mass of the Carbon sample is:
- (70/100 x 11) + (30/100 x 13) = 7.7 + 3.9 = 11.6
[this is not the true atomic mass of carbon, it is merely illustrative]
[edit] amu to kg
the number on the page for u didn't agree exactly with the CODATA value referenced at the bottom. CODATA is state of the art, I have changed it to the CODATA value.
[edit] Nucleus or Atom?
Is it 1/12 of a C12 nucleus or atom? I can't remember my high school physics, and some sites say it's "nucleus" and a few say it's "atom".
It's both, the mass of the atom is the mass of the nucleus, since the mass of the electron is negligible. Mchmike 03:19, 19 October 2006 (UTC)
no its not negligible. the electrons weigh something. In order to be accurate, the 1/12 must be defined as something, and the pure number 1/12 is infinitely percise, hence it must be 1/12 of either the nucleus or atom. 65.185.93.86 (talk) 21:31, 22 May 2008 (UTC)
No. It is definitely the atom. The mass of the electron is about 1/2000 of the mass of a nucleon, much larger than the accuracy to which nuclear masses can be determined. It is negligible for some purposes, but not for all.
[edit] atomic mass unit or Dalton' mass
I read in two college texts that the absolute mass of the atomic mass unit is 1.66054E-24 grams. Wouldn't that make kilograms .00166054E-27? RAW 18:54, 24 April 2007 (UTC)
- 0.00166054E-27=1.66054E-30. You are shifting by 6 decimal places instead of three. The article is correct 1.66054E-27kg==1.66054E-24g--Nick Y. 20:06, 24 April 2007 (UTC)
[edit] Dalton vs g/mol
Perhaps this article could be edited to more obviously show the relation between Daltons and the molecular mass in g/mol? Roddyboy 03:28, 15 May 2007 (UTC)
- The relation which you are addressing is a very impractical but very simple relation that I would advise you to be uninterested in. It is somewhat addressed in the example just to demonstrate the definition. Perhaps you mean the relationship between the molecular mass in daltons and the molar mass in g/mol? I have added language to make this more clear without going into detail since it is really should not be a part of this article. This relationship is really very, very complicated and depends on multiple molecular masses and statistical distributions of isotopes and averaging across different locations around the globe etc.--Nick Y. 18:57, 15 May 2007 (UTC)
- Cool thanks for that. Yeah I meant the molar mass in g.mol-1 vs. the molecular mass in Daltons. It's a very clear explanation now :-) Roddyboy 03:18, 16 May 2007 (UTC)
