Talk:Relative atomic mass

Uncertainty

The article uses the notation of putting the uncertainty in parentheses, without explaining this notation. I came to the article while reading the articles on some elements hoping to find such an explanation.

The article links to Measurement uncertainty with a link label of "uncertainty", but there's no explanation there, either (I had guessed the notation was to do with uncertainty). In fact, there's an explanation in Uncertainty#Measurements. Isidore (talk) 13:16, 8 May 2013 (UTC)

Fix in lede

The lede says that relative atomic mass is used as a synonym for standard atomic weight and that really isn't right, unless it's incorrectly used. Relative atomic weight is the same as atomic weight, but it's the "standard" part of "standard atomic weight" that makes the terms potentially different. The "standard" refers to the source, and here it is:[1]

Standard atomic weights are:

"Recommended values of relative atomic masses of the elements revised biennially by the IUPAC Commission on Atomic Weights and Isotopic Abundances and applicable to elements in any normal sample with a high level of confidence. A normal sample is any reasonably possible source of the element or its compounds in commerce for industry and science and has not been subject to significant modification of isotopic composition within a geologically brief period."

Values for relative atomic masses from deep rocks, meteorites, or geologically old stuff, won't be "standard". "Standard" means it's what you can expect from stuff on your chemical shelf, but the isotopic composition from an odd source can always fool you, and be out of standard rage. So the lede needs to be fixed.

All this is not helped by the fact that people often loosely use "atomic weight" to mean "standard atomic weight" (what you see on periodic tables and in WP articles on elements), and also that (probably for brevity's sake) the term "standard atomic relative mass" isn't used much, even though that's what this refers to, if you insist on using relative atomic mass. Add to that, that the term "relative atomic mass" is a lousy one, since it actually refers to an idea something like "isotope-weighted mean elemental atomic mass (on the C-12 scale)".

The section differentiating these terms needed some fixing and I found it residing in the atomic mass article, where it really didn't belong. I've improved it and moved it here. I'll fix up the lede to agree with it, and that will be a start on both these articles to get them at least minimally error-free. SBHarris 02:55, 9 May 2013 (UTC)

Historical section

What garbage. What is historical about the current IUPAC recommendation?? Nothing. This section either needs complete rewrite or removal. Where is the discussion of the O-16 scale??????? And the standardization?> This is really embarrassing! If you have nothing to say, say nothing.72.172.1.250 (talk) 14:02, 28 August 2013 (UTC)

We moved the O-16 stuff (pre-1961) to the article on unified atomic mass unit, where it belonged. The "unified" part of unified atomic mass unit is what differentiates C-12 based standardization from O-16 standardization, which was the basis of the (old) amu. Now, we have just the u, aka dalton, based on C-12). SBHarris 00:20, 10 October 2014 (UTC)

Confusion in the Table

The second paragraph points out that relative atomic mass is "technically different" from standard atomic weight. The third paragraph states that the table includes standard atomic weights, but the table's heading states that the numbers are relative atomic masses. Either the third paragraph, the table's heading, or the statement contrasting relative atomic masses and standard atomic weights needs to be corrected. HankW512 (talk) 16:44, 10 March 2014 (UTC)

The table you speak of no longer appears to be part of the article. Indeed relative atomic mass is "technically different" from standard atomic weight. It is merely atomic weight. SBHarris 03:58, 7 September 2017 (UTC)

Goldbook

Wouldn't it be better to use the goldbook template instead of the current links? For example: IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "mixing ratio". doi:10.1351/goldbook.M03948 --RolfSander (talk) 07:07, 8 April 2014 (UTC)

Good non-terrestial examples

We need examples of A_r that are not naturally terrestial (i.e., are not used by CIAAW).

• [2]

Potassium isotopic evidence for a high-energy giant impact origin of the Moon

Kun Wang & Stein B. Jacobsen Nature 538, 487–490 (27 October 2016) doi:10.1038/nature19341 Published online 12 September 2016

Shows figure 1 for ⁴¹K abundance:significant diff between moon, Earth and chondrites.

-DePiep (talk) 13:53, 9 March 2017 (UTC)

Also a section added for argon, which differs greatly in atomic weight between Earth and the Sun (and most of the universe.) SBHarris 03:50, 7 September 2017 (UTC)

The awful problem that chemists use "standard atomic weight" yet refer to it as "atomic weight."

See my note above from 2013. The lede definition keeps drifting. Standard atomic weights aren't atomic weights, even thought it's a very common error.

It isn't a lot of help when the usual term for a thing is wrong by reason of slang. What is seen in interval notation on periodic tables is the STANDARD atomic weight. That is the value of atomic weight you expect from many samples on Earth, and hence the interval! The atomic weight of a SINGLE sample in a lab can be determined far more accurately with a mass spectrograph, even though usually more than one isotope is being evaluated, and their weighted sum used. That atomic weight can differentiate between samples, using stable isotope ratios. For example, it is differences in atomic weights of carbon from natural testosterone vs. artificial testosterone (which has a carbon atomic weight that looks like a plant) that allows doping commissions to tell if testosterone is taken artificially. Yet all these values are within the "standard atomic weight" for carbon seen on the average periodic table. That is why the two terms are different.

The term "relative atomic mass" is the same as "atomic weight". It is NOT the same as "standard atomic weight." That latter term would need to be "standard relative atomic mass" which is so long it is rarely seen. This is one reason that "atomic weight" continues to hang on. SBHarris 03:30, 7 September 2017 (UTC)

• I find your today's edits not all an improvement. not this strong -DePiep (talk) 07:14, 20 September 2017 (UTC).
• "The lede definition keeps drifting" — FYI, in March 2017 standard atomic weight at last got its own article, so this article text should change. Your 2013 post you refer to is not applicable to this article relative atomic mass any more. And btw, the 'lede definition' as you call it should be taken from article body text, not as a stand alone statement. The lede now is way too lonng (mostly because you keep mentioning and explaining the atomic weight issue, without adding info, and because you re-added standard atomic weight definition which should be out or very short). -DePiep (talk) 14:50, 7 September 2017 (UTC)
• You say: Standard atomic weights aren't atomic weights - I beg to differ. A standard atomic weight is a physical quantity, correctly expressed as a relative atomic mass (A_r). It's just a more specific one (A_{r, standard}, I wrote elsewhere). Just as one can use "speed" (physical quantity) more specific defining some "average speed". -DePiep (talk) 15:06, 7 September 2017 (UTC)

  Sbharris: Actually, you made a big improvement: stating that 'atomic weight' is 'relative atomic mass'. So I did [3]. Now the sources (especially CIAAW 2016) are much clearer to understand (and correct).

From here on, we could refine on which fact should be in which article (and should not be in). Also, which of these should end up in a lede. As we know, for the average reader the standard atomic weight is most relevant, while atomic weight is just a more general measurement (I say coming from WT:ELEMENTS). Also the "don't confuse with"-list could be improved. (I'm not that enthousiastic about the 'scientists are doing it wrong'-note you made). -DePiep (talk) 07:14, 20 September 2017 (UTC)

References