Talk:Dalton (unit)

Dalton as a size unit

Can someone please explain the units and use of parentheses used in this equation from the article: 1 u = 1.660538782(83)×10−27 kg = 931.494027(23) MeV/c² The article is supposed to be accessible and I don't think this is. 139.133.7.37 (talk) 12:25, 8 November 2008 (UTC)

The parenthetic digits represent the measurement uncertainty in the least significant digits of the mass. The relationship between atomic mass units and kilograms is explained in the article, whilst MeV/c² represents mass through mass-energy equivalence. Eutactic (talk) 05:42, 26 August 2009 (UTC)

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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?

As many proteins are more or less globular (round), mass and diameter will be somewhat correlated. Mass limits like in your example are proximates like most numbers you find in biology. 139.133.7.37 (talk) 12:20, 8 November 2008 (UTC)

Also the mass of any molecule can be converted in its number of protons + electrons, eg 1kDa is roughly 1000 protons and neutrons, and that is probably a good proxy for how large the protein will look like. I have read somewhere that after a 1MDa proteins don't even diffuse any more. — Preceding unsigned comment added by 188.223.9.243 (talk) 23:43, 30 June 2011 (UTC)

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Why did they choose the AMU convention of 1/12 of C12 rather than the original 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)

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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.

"Pure" chemistry is rarely concerned with molecules larger than ~500 Da, while life sciences are usually mainly concerned with molecules larger than 1000 Da. When you use prefixes like kilo and mega a lot, having a simple name for the unit like "dalton" makes life easier. I've also found that chemists who work a lot with polymers (which tend to have very high molecular weights) also tend to use dalton. For physicists, this is rarely a problem. - Alltat (talk) 18:37, 24 April 2012 (UTC)

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Physicists have the opposite problem - small values rather than large values. When they talk about mass deficiency rather than binding energy, it might well be appropriate to use mDa or μDa rather than milli or micro atomic mass units. Martinvl (talk) 18:56, 24 April 2012 (UTC)

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How do you change Atonic mass into pounds?

via Kilograms.

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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)

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]

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.

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, it's 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)

C12 has 6 electrons, I guess they are accounted for in the 12 daltons that a C12 weights, since the definition mentions the electronic ground state. 80.215.74.36 (talk) 12:15, 22 October 2022 (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.

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)

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)

The most common use of 'Daltons' is as a synonym for g/mol. When someone talks about a 254 kDa protein, they mean it has a molecular mass of 254,000 g/mol. I think this article needs to make this clear.27.54.43.66 (talk) 03:46, 28 May 2011 (UTC)

The statement "Da = g/mol" occurs often in chemistry texts and elsewhere. Since the LHS has the dimension of mass and the RHS has the dimension of mass/amount, it is, of course, incorrect. This misconception comes about because of the missing atomic-scale unit for amount, namely one entity, symbol ent. The number of entities in a sample of a substance X is given by N(X). The corresponding amount of the substance is given by n(X), which is an aggregate of N(X) entities:

n(X) = N(X) ent

where ent represents the smallest possible amount of any substance and is the appropriate atomic-scale unit for amount. The so-called molar mass of the substance is defined by:

M(X) = m(X)/n(X) = [N(X)m_av(X)]/[N(X) ent] = m_av(X)/ent

where m_av(X) is the sample-average entity mass, written as A_r(X) Da, where the relative atomic-scale mass, A_r(X), can be found from catalogues such as the Periodic Table. Thus:

M(X) = A_r(X) Da/ent

where Da/ent, dalton per entity, is the appropriate atomic-scale unit for molar mass.

Since one mole is given by:

mol = 6.02214076 x 10²³ ent

and one gram is (for all practical purposes) given by:

g = 6.02214076 x 10²³ Da

we see that it is dalton per entity that is (for all practical purposes) equal to gram per mole (or kilogram per kilomole):

Da/ent = g/mol = kg/kmol

So, for the molar mass, we (should) have:

M(X) = A_r(X) Da/ent = A_r(X) g/mol = A_r(X) kg/kmol

It is clear from this why the dalton should have been redefined, along with the mole, so that it is exactly related to the (redefined) kilogram:

"Da = (1/6.02214076 x 10²⁶) kg, exactly"

In which case, the molar mass constant would be exactly 1 g/mol = 1 kg/kmol. If necessary, the "unified atomic mass unit", u, could be decoupled from the (exact) dalton and retained by its definition in terms of the (inexactly known) carbon-12 atomic mass.

And, in case anyone was wondering, the poorly understood Avogadro constant, N_A (not to be confused with the Avogadro number), is exactly one per entity: N_A = 1/ent. And is otherwise irrelevant!

[Over the past couple of decades or so, I have formally proposed introducing ent as the atomic-scale unit of amount (to be accepted for use with the SI) and redefining the atomic-scale unit of mass, dalton, exactly in terms of the (now redefined) fixed-h kilogram a number of times in published papers, but (so far) to no avail.]

In summary, it is important here to avoid the false claim that "Da = g/mol". Boppennoppy (talk) 20:57, 12 November 2024 (UTC)

Other units

The author is correct when writing that the molecular mass of water is 18.0106 g/g-mol. However, in some industries (especially petroleum refining) in the United States (perhaps elsewhere), lb/lb-mol is the preferred term. Furthermore, there it is called molecular weight. As one could see by inspection, 1 g/g-mol = 1 lb/lb-mol. —Preceding unsigned comment added by 69.42.7.158 (talk) 02:09, 11 August 2008 (UTC)

Atomic mass unit

Why is only 1/12th of the carbon atom taken for amu? Why not of any other element? —Preceding unsigned comment added by 202.125.143.73 (talk) 16:48, 21 August 2008 (UTC)

This is because A_r(H) = 1/12 of A_r(carbon-12) = 1. Remember that atomic weight (A_r) is a ratio. It is the molar mass (M) = A_r * M_u, where M_u is the molar mass constant, 1 gram/mole. Thus, M(H) = 1 g/mole = 1 amu. --Bsodmike (talk) 20:36, 18 July 2009 (UTC)

If you do a regression analysis of the reported mass values of the incremental 4 nucleon (alpha particle?) increases of the A = 2Z elements you get a least squares curve of expected mass values over this limited range of atomic mass values. It should be noted that this curve gives values for C12 and O16 which is slightly greater than their reported values, and that the reported O16 value is closer to the least value curve than the C12 curve. This might indicate a tendency for the reported AMU values of atomic masses to be biased towards underestimating the true values in both cases, but that the estimating values for the O16 values would be more correct.WFPM (talk) 14:29, 31 July 2009 (UTC)

I believe that originally the physicists used hydrogen, but the chemists used oxygen, so as a compromise both disciples agreed to use carbon. Martinvl (talk) 10:51, 22 January 2010 (UTC)

The physicists used ¹⁶O = 16, while the chemists used O = 16 (at natural, and hence variable, isotopic composition). ¹²C = 12 was indeed a compromise solution: the full story can be found in this free-access article. Physchim62 (talk) 17:57, 12 August 2010 (UTC)

AMU reversion (From User talk:Martinvl)

Sorry, referring maybe I am being a bit tired/dense, where does it say that the preferred usage for large or small values is Dalton? It says it is "often used" sure, but the text is suggesting it is somehow preferred? (diff in question) User A1 (talk) 21:54, 11 August 2010 (UTC)

The use of prefixes is referred for all SI units. (I am a part-time physics teacher so I come across this problem regularly).

Sorry, I think we are not quite on the same topic -- I am suggesting that the citation does not indicate that dalton is preferred over the AMU unit "u", which is the implication in the sentence. For example. what prevents someone from writing "ku" rather than "kDalton"User A1 (talk) 10:34, 12 August 2010 (UTC)

You are right, the BIPM reference does not prefer one above the other. However it appears that the ISO reference (which was added by another editor) does. As this is the case, I think it best that this discussion be continued on the article's talk page. Martinvl (talk) 11:11, 12 August 2010 (UTC)

I'm not convinced that is right either. Looking at page 126 of this document the unified atomic mass unit "u" and "Da" are both acceptable. User A1 (talk) 12:49, 12 August 2010 (UTC)

The BIPM document is dated 2006, the ISO document 2009. Since I do not have access to the ISO document (or rather I am not prepared to pay CHF142.00 for it), I am unable to compare the two. If somebody is able to check the actual ISO 80000:2009 source (or quote and authority who has done so), I will accept their word for it. Martinvl (talk) 15:17, 12 August 2010 (UTC)

Unfortunately I am also unwilling to pay for the ISO document, and thus cannot access it. In light of the fact that the currently available evidence does not support the statements, I have removed the comments about which is preferable. I feel it is better to say nothing than to say something which is possibly incorrect User A1 (talk) 15:44, 12 August 2010 (UTC)

My understanding is that both usages are equally acceptable. There is a definite preference among biochemists, molecular biologists and polymer scientists for the name "dalton", simply because they work in kilodaltons. Chemists, who tend to work in the range 1–1000 Da, usually ignore the unit or use g/mol (which is numerically equivalent). I've never seen "millidalton" used in practice, but it's not incorrect and it might catch on in the future. It's not a big practical issue, and so we shouldn't give it WP:UNDUE attention. Physchim62 (talk) 18:13, 12 August 2010 (UTC)

I have reinstated the previous version because:

• Just because the ISO standard is not available on-line is no reason to disregard it. In fact, it is a Wikipedia principal to assume good faith unless proven otherwise. The way in which the sentence was written is sufficent for me to assume good faith, at least until I have a chance to verify the standard for myself.
• I Googled "kilodalton" and found a number of references relating to enzymes and the like. This is sufficient reason to keep it in place.
• I also Googles "millidalton" and found a number of real references, but they were buried inside scientific papers. Again this is sufficient reason to keep it in place.

Martinvl (talk)

Good faith has nothing to do with this; I don't think anyone is doing anything intentionally wrong, however I do think we need to cite what we say. Quoting the first line of WP:VER "The burden of evidence lies with the editor who adds or restores material". We don't have the evidence to support this at all. User A1 (talk) 18:36, 13 August 2010 (UTC)

I found a number of referneces to millidaltons in various conversion programs. I found at least one instance where I saw the word "millidalton" in an article. This is sufficient to satisfy WP:VER. The references that I came across when Googling showed extracts of text from various scientific papers. When one linked to the page concered, the article abstract and sometimes the first page were visible. The reader had to pay to view the rest (unless they were suibscribers to the service). The context nevertheless satisfied me that the phrase shown by Google Search was in fact a sentence from the article concerend. For example, Google turned up the following phrase "investigated at the millidalton level or better, allowing one to resolve 'micropeaks' arising ... millidalton level. At this level, a single nominal isotope" here. The abstract does not contain this phrase, but I am satisfied that the downloadable PDF does. Martinvl (talk) 20:20, 13 August 2010 (UTC)

You guys may be interested in the following:

• http://www.bipm.org/utils/common/pdf/CCU15.pdf (Minutes of an SI committee) "The dalton (symbol Da) is used as a name for the unified atomic mass unit. It is widely used by polymer chemists and biochemists (see footnote (c) in Table 7 of the current Brochure). The CCU acknowledged that the name Dalton has advantages over ‘unified atomic mass unit’: it is shorter and works better with prefixes. The ‘unification’ between chemists and physicists which gave the unit its name is now of historic interest only. A decision was taken to introduce the dalton into Table7, according it equal status with the unified atomic mass unit."

• http://www.iupap.org/commissions/c2/reports/ga-05.html "In response to the increase in the use of the name “dalton” for the unified atomic mass unit among chemists, it was suggested by IUPAC that the unified atomic mass unit (u) be renamed the “dalton” (D). The definition of the unit would remain unchanged as one-twelfth the mass of a neutral 12C atom in its ground state. After considerable discussion it was agreed that both units, u and D, should be allowed official use and that the situation be reexamined in the future to evaluate whether the use of these units in the scientific community would suggest the selection of one of these names over the other. Some members have argued that there is no strong reason to change the name of this unit."

• http://www.iupap.org/commissions/interunion/iu14/ga-05.html (quote attributed to IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), and Nomenclature Commission of IUB (NC-IUB),.)

"A suggestion has been made in the CCU (communicated to C2 through Brian Petley), that the time has come to replace the name and symbol of the unified atomic mass unit, u, with dalton, Da. The grounds are that the current name is a mouthful and the need to emphasize the concept of "unified" is long gone. The dalton is widely used in chemical mass spectrometry community (e.g. bio-chemistry). Its use will also bring the polymer chemists into the SI community. There is possible confusion with the astronomical unit ua, and people want to use u or U to denote the unit one. There was considerable comment on this matter from many of the SUNAMCO members. In the short term the proposed change simply endorses the present reality that both the atomic mass unit and Dalton are in use."

• http://www.chem.qmul.ac.uk/iubmb/newsletter/misc/moles.html (attributed to IUPAC) to "approve the name 'dalton' (symbol: Da) as an alternative to the name 'atomic' mass unit' (symbol: u)". In asking other IUPAC bodies their views on this proposal, the Interdivisional Committee for Nomenclature and Symbols states that it finds merit in the proposal and adds the following arguments and notes.
  • Arguments
  • 1. The word 'dalton' is already used in the biochemical literature [see LT.Edsall, Nature (Lond.) 228, 888-889 (1970) and M. A. Paul, Nature (Lond.) 229, 142-143 (1971)].
  • 2. The name 'atomic mass unit' is unwieldy. Its symbol (u) is strange in that this one unit should be symbolized with a 'u' for unit, and some of its multiples and submultiples, e.g. 'mu', may be confusing.
  • 3. The name 'dalton' and symbol 'Da' would allow adjectival use, e.g. a 144-Da fragment, a 15-kilodalton molecule, a 2.6-MDa ribosome.

It does seem to me that the powers that be (BIPM, IUPAC, IUPAP) are moving towards adopting Dalton more widely, but not doing anything to deprecate the AMU (they rarely deprecate any unit). I hope that helps. Lightmouse (talk) 20:44, 13 August 2010 (UTC)

I have rearranged all of the relvant documents into chronmologial order and in my view they show that the scientific world is moving toward the adoption of the dalton over the amu. I don't know who added the statement about ISO 80000:2009 deprecating the amu, but given the chronology of the other documents, I would, on the balance of probablity, accept that statement as being "probably true". I would like to re-instate it. If there is disagreement, I plan to go to the British Library and I will look up the ISO document and catalogue it fully.

Once all the evidence had been arranged into chronologial order, the last sentence looked like it was pure WP:POV so I removed it.Martinvl (talk) 20:32, 14 August 2010 (UTC)

Hi, I am not sure where the POV comes in. Anyway, the current wording is a vast improvment over what was previously there, and as far as I am concerned, further discussion is not needed. User A1 (talk) 23:17, 14 August 2010 (UTC)

Be careful here. The "amu" is clearly deprecated (in 1961). The "u": maybe, maybe not. Small note: MilliDalton is in fact in common usage as some googling has shown. It's use arises from differences between masses with modern, highly accurate measurements.--Nick Y. (talk) 07:21, 17 August 2010 (UTC)

Are there any references of mu being used? I believe that one of the attractionsof using the dalton was that mDa could not be confused with anything else, whereas the u or U is used in a number of different applications - for example, my insulin (I am diabetic) has a strength of 100 u/ml. That is clearly why the bio-chemists disliked using "u". Martinvl (talk) 20:17, 20 August 2010 (UTC)

The implication from the SI brochure is that prefixes are not used with u, no doubt for the sort of reasons you describe. When I read your edit summary, I thought you were referring to the Greek letter µ! Still, I did find this authoritative example of the use of "micro-u" (it dates from 2003, and is the most recent update of the international list of nuclide masses). Physchim62 (talk) 20:25, 20 August 2010 (UTC)

Example of SI prefix used with u. See figure 1. However, an example is not a proof in arbitrary convention systems.User A1 (talk) 21:59, 20 August 2010 (UTC)

Regardless prefixes with "u" are not commonly used, which makes its use not notable. Its lack of use and more accurately the ease of confusion created by its use however is notable due to the debate around units and symbols.--Nick Y. (talk) 15:32, 23 August 2010 (UTC)

I also corrected a problem with the chlorine example in the definition section. The numbers given on a periodic table are *not* atomic masses and do not use the atomic mass unit. They are atomic weights or more precisely standard atomic weights and they are in g/mol, the same units as molar mass. --Nick Y. (talk) 15:44, 23 August 2010 (UTC)

Renaming this article to "Dalton (unit)"

The following discussion is an archived discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

No consensus to move. Vegaswikian (talk) 18:19, 30 August 2010 (UTC)

Atomic mass unit → Dalton (unit) — This is one of the earliest articles in Wikipedia (2002). The article "Dalton (unit)" had a short life in 2005 before being merged with this article on grounds that "It is often used in biochemistry and molecular biology although it was never approved by the Conférence Général des Poids et Mesures CGPM". Since then a number of things have happened (referenced in article):

• A few days prior to the merger, the International Union of Pure and Applied Physics endorsed the use of the dalton as an alternative to the unified atomic mass unit.
• In 2006 the Conférence Général des Poids et Mesures endorsed the use of the dalton as an alternative to the unified atomic mass unit
• In late 2009, ISO 80000-1:2009 (General) cited the dalton as having "earlier [been] called [the] unified atomic mass unit u".
• At the same time ISO 80000-10:2009 (atomic and nuclear physics) endorsed the use of the dalton as an alternative to the unified atomic mass unit

In addition, the University of Oxford Style Guide for Life Sciences listed the dalton as an allowable unit (along with SI), but did not mention the unified atomic mass unit. This suggests to me that that we should at least be considering moving the text of this article to the article "Dalton (unit)". My assessment is that since the two articles have been merged, there has been a drift towards using the dalton in preference to the unified atomic mass unit and that the split in the literature is now 51% to 49%. (I am not going to justify these figures). Martinvl (talk) 19:42, 23 August 2010 (UTC)

Weak oppose. Either name is acceptable, but I think "atomic mass unit" is still the more common, even if "dalton" is obviously gaining ground. Also, by keeping the article where it is, we avoid a disambiguated title. None of this is conclusive, of course, which is why my oppose is only "weak". I would say that, IMO, the question of the article title is quite secondary to the appalling state of the article at the moment: I am very tempted just to rip it up and start again. Physchim62 (talk) 17:39, 24 August 2010 (UTC)

• Oppose any rename based on the decisions of standards bodies. WP should not follow standards bodies, but rather scholarly usage. If usage has really changed, that's different; I'm not in a position to know that. --Trovatore (talk) 18:42, 24 August 2010 (UTC)
• Oppose I think this could be best breached in a few years time -- we seem to be jumping the gun here. The standards bodies are not deprecating AMU, and are only suggesting "alternative" or "allowance". On the other hand, if the standards bodies actually deprecate AMU, I am all for a rename. User A1 (talk) 19:05, 24 August 2010 (UTC)
  • Comment. I disagree with your last remark. What standards bodies do, per se, is irrelevant to us. --Trovatore (talk) 19:09, 24 August 2010 (UTC)
• Comment I agree with usage as primary to namespace. It is hard to search for "u" or "Da" accurately. "Molecular mass 'atomic mass unit'" returns 100 hits but "Molecular mass Dalton" returns 3,326 hits on pubmed. Inconclusive but clearly indicative. In my experience as an academic in both chemistry and biology "u" is extremely uncommon, less common than "amu" which is simply wrong. "Da" is very common, near universal in molecular biology and very common in chemistry. "atomic mass units" spelled out completely is still fairly common as well as. Those that deal with molecular and atomic masses use Daltons most commonly. --Nick Y. (talk) 20:07, 24 August 2010 (UTC)
• Comment by proposer My initial analysis suggested that the chemists (and in particular biochemists) tended to use the dalton, whereas the physicists tended to use atomic mass unit - hence my questions.

I agree with User:Physchim62 that a rewrite would be appropriate, so it might well be an opportunity to reflect both names equally.

Finally, how should we measure "scholarly usage"? Actual usage in articles (some of which might be several years old), or the current style guides of the top journals (which should give the current view)?

Martinvl (talk) 20:20, 24 August 2010 (UTC)

Actual usage in articles. It's fine (actually it's better) if an encyclopedia is a bit on the conservative side as regards linguistic usage. --Trovatore (talk) 20:29, 24 August 2010 (UTC)

• Oppose. As long as the standard bodies are describing Dalton as an "alternative" we should stay where we are. I disagree that "What standards bodies do, per se, is irrelevant to us". They are very relevant and we should only not follow them in unusual circumstances. They are our prime sources for units. --Bduke (Discussion) 21:18, 24 August 2010 (UTC)
  • Why? What matters is what actual workers in the field do, not what some organization does. Insofar as actual researchers and engineers follow the recommendations, well and good. In cases where they conflict (say, as regards the term micron), we should follow what is actually done. --Trovatore (talk) 21:54, 24 August 2010 (UTC)
    • You're assuming that standards organizations are always proactive (imposing standards) rather than reactive (standardizing what is already widely accepted). On this issue, the various standards organizations seem to be reactive – that is to say that both namess are used, neither of them are ambiguous in anyway, so let's see which one is preferred (IUPAP was quite explicit in the "let's see which one is preferred" part). I agree that Wikipedia should not slavishly follow the standards organizations, but we cannot discount them either: as a minimum, the existance of a standard should be noted in the article, even if we don't follow it ourselves. Physchim62 (talk) 00:10, 25 August 2010 (UTC)
  • Standards organizations say that the percent sign should be spaced (e.g. "5 %" rather than "5%"), though hardly no-one else does that when writing in English. Should we follow them on this, too? A. di M. (talk) 12:51, 27 August 2010 (UTC)
• Oppose per Bduke. The dalton (Da) is an alternative to the atomic mass unit (u, amu), not the other way around, and use of u/amu is neither deprecated, nor discouraged. While the dalton is gaining grounds, and the article should reflect that and the state of the Da vs. u debate, WP:CRYSTAL applies. Headbomb {talk / contribs / physics / books} 22:10, 24 August 2010 (UTC)

• What I am saying is that in many fields the dalton has overtaken the atomic mass unit. The question is "how far ahead must the dalton go before we give it preference?" Martinvl (talk) 13:09, 27 August 2010 (UTC)

• Oppose per IUPAC Gold Book.[1][2] --Kkmurray (talk) 00:40, 27 August 2010 (UTC)

• These refererences are both based on a 1997 publication. Martinvl (talk) 13:09, 27 August 2010 (UTC)

• Very weak oppose. In my experience "atomic mass unit" is more common, but probably that's because I'm a physicist and if I were a biochemist my experience would be different. Anyway, if both terms are sufficiently in wide usage (though in different fields), I'd leave the article alone per WP:MOS#Stability of articles; on the other hand, given that chemists use this unit much more often than us physicists (who usually use GeV/c² for masses of that size), a case could be made that their usage is more relevant than ours. (BTW, I've added the requested move template at the top of the thread.) A. di M. (talk) 12:51, 27 August 2010 (UTC)

The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Rewrite

I have made a number of changes to the initial rewrite. Firstly I have rewritten the lede so that it only discusses the atomic mass unit without mentioning its relationship to the mole. The section, formerly called "Definition and Measurement" needs considerable rework. I have renamed it "Relationship to the mole" as that is what the content appears to be. Thuis section could well be expanded to show how it is used in the world of chemistry. The content certainly has nothing to do with measurement as it can be measured by any number of different methods. A similar section could be used to show how it is used in the world of physics, looking at Mass deficiency and the like.

I also think that the History section needs considerable expansion, showing how the difference definitions were brought together and why it is called the unified atomic mass number. Martinvl (talk) 19:56, 25 August 2010 (UTC)

I agree that there's plenty more that we could put in the History section: there are details and references at atomic weight and amount of substance that could be used as a basis.

IMHO, much of the problem with the old article was that it went into too much rambling (often factually incorrect) about "how it is used in the world of chemistry". It's a mass unit, it's used to measure mass, that's about it! You say that "it can be measured by any number of different methods" – I disagree: the Avogadro constant can be measured by several different methods, but the dalton is (at present) determined by the N_A, and always has been. You cannot measure atomic mass directly, you have to work through relative masses (mass ratios): that, indeed, is the utility of the dalton, because you can measure the mass ratios far more accurately than you know the conversion factor into kilograms. Physchim62 (talk) 02:00, 26 August 2010 (UTC)

We must be aware that there is a distinct possibility that within 18 months, the kilogram is going to be redefined in terms of the dalton and Avagadros number. This will neccessitate a rewording of sectiosn of the article which we should attempt to minimise. Martinvl (talk) 05:23, 26 August 2010 (UTC)

If the kilogram is redefined in terms of a fixed number of carbon-12 atoms (as the ISO seems to want), then the whole article will have to be rewritten because the dalton will become a fixed submultiple (a bit like the angstrom is a fixed submultiple of the metre). The other proposals for the "New SI" would have much less effect. Physchim62 (talk) 15:02, 26 August 2010 (UTC)

We should be aware that a wiki article's inertia is a lot less than that of a standards body. Also, we should not try to pre-emptively supply information. Let us worry about future hurdles in the future. We all seem to be better at writing talk pages than articles, myself included. User A1 (talk) 15:13, 26 August 2010 (UTC)

Agree (especially the last comment!) There's probably space on WP for an article about the "New SI", and I'm trying to pull one together, but there are other issues to focus on here – like how this article can (at present) simply not mention the atomic mass constant, for example! Physchim62 (talk) 16:38, 26 August 2010 (UTC)

I had been thinking about how to incorporate the possible changes in SI into Wikipedia and I like Physchim62's idea of a new article New SI and that all other SI articles shoudl reference that article. Back to Atomic Mass Units - I think that the rewrite has managed to expunge atomic mass constant from its text. Apart from the History subsection, I see no need to re-introduced it. Moreover, I would urge all authors to keep in mind that there are likely to be changes to SI in 2011. Martinvl (talk) 11:12, 27 August 2010 (UTC)

I disagree with you on that last point, but this section is getting long, so... Physchim62 (talk) 13:32, 27 August 2010 (UTC)

Atomic mass constant

The conversion factor between daltons and kilograms has a name, it's called the atomic mass constant: I find it remarkable that the article doesn't mention this (because it's been removed). Nor does the article give any information about how the value of this conversion factor is calculated: the equation m_u = M_u/N_A (referenced to the CODATA paper) needs to be reinstated, or readers are left with the impression that you can weigh a carbon atom. Physchim62 (talk) 13:32, 27 August 2010 (UTC)

My understanding is that the atomic mass constant is a conversion between atomic weights (not masses) and kilograms. Atomic weights are dimensionless and are defined as the ratio of the mass of the atom/molecule under consideration to 1/12 of the mass of a Carbon 12 atom. The atomic mass constant therefore has the dimensions of kilograms. Martinvl (talk) 20:57, 30 August 2010 (UTC)

Hmm, the definition you give sounds more like a relative atomic mass than an atomic weight, although the two terms are used interchangeably (wrongly, in my opinion, but I shaln't deny that they are). In any case, you multiply a dimensionless mass-ratio by a constant with the dimension mass to get an absolute mass. That constant is m_u:

m_u = M_u/N_A ≡ 1 Da

If m(X) is the mass of an atom X, and A_r(X) is the relative atomic mass of that atom (and not the quantity that chemists call "atomic weight"), then

m(X) = m_uA_r(X)

for any unit of mass you choose. The distinction is important because you usually know A_r(X) far more precisely than m_u or m(X) unless you're measuring m(X) in atomic mass units (in which case, the conversion is trivial): hence the utility of the atomic mass unit (or dalton) in physics or mass spectrometry. Physchim62 (talk) 21:25, 30 August 2010 (UTC)

If you look up Atomic Mass Constant [[3]], you will see a four different values - the units being u, kg, MeV and J. Maybe the Atomic mass constant page needs to be tidied up. Martinvl (talk) 05:28, 31 August 2010 (UTC)

Yes, of course, m_u is a dimensional physical constant, it has an infinity of numerical values depending on your choice of units. If you look closely, you'll also see that the uncertainties change depending on your choice of unit. I don't really see your point here. Physchim62 (talk) 10:47, 31 August 2010 (UTC)

I've added the energy equivalents and a note on their use to atomic mass constant; just as well I took a look, because the equation to determine the value was upside down! Physchim62 (talk) 11:52, 31 August 2010 (UTC)

Kendrick mass and improper synthesis

I flagged this edit [4] as improper synthesis for the reasons outlined in this RfC: RfC:_Is_Kendrick_unit_original_research. --Kkmurray (talk) 17:26, 28 October 2010 (UTC)

As explained in RfC:_Is_Kendrick_unit_original_research, the Kendrick mass unit is sourced from a single source [5]. It therefore per definition cannot be a synthesis. Therefore I removed the flag. Kehrli (talk) 21:43, 28 October 2010 (UTC)

I removed Kendrick unit from the infobox. --Kkmurray (talk) 18:44, 16 March 2011 (UTC)

Infobox

I have modified the unfobox to show the dalton as an alternative to the amu, because firstly, it is just that and secondly, the article "Dalton (unit)" redirects to this artcile. Martinvl (talk) 05:07, 27 June 2012 (UTC)

This sentence could be improved

Section "Terminology", 4th bullet: "In 2006 ... the CIPM cataloged the dalton alongside the unified atomic mass unit as a "Non-SI units whose values in SI units must be obtained experimentally: Units accepted for use with the SI".[2] "

• In the linked pdf, table 7 on p. 126 of the book (p. 34 of the pdf) is headed "Non-SI units whose values in SI units must be obtained experimentally". The additional sentence "...: Units accepted for use with the SI" is not in the table header (it appears earlier) and seems to make things unnecessarily complicated.
• Also, there is a clash between singular ("the dalton alongside the unified atomic mass") and plural ("Non-SI-units").
• The word "alongside" seems badly chosen to me, since dalton and u are the same.

Could one of the main authors straighten this sentence out? Thanks for your efforts, and best regards: Herbmuell (talk) 00:54, 11 May 2015 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Dalton (unit)/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Please explain something to me. If amu "is defined to be one twelfth of the mass of an unbound atom of the carbon-12 nuclide, at rest and in its ground state" and Avagadro's constant is "the number of carbon-12 atoms in 12 grams (0.012 kg) of unbound carbon-12 in its ground state" then why is 1 amu given as: 1 u = 1/NA gram = 1/ NA gram (where NA is Avogadro's number) Shouldn't it be: 1 u = 1/12 (1/NA) 66.245.41.18 18:33, 30 June 2007 (UTC)

Last edited at 21:47, 4 February 2010 (UTC). Substituted at 08:33, 29 April 2016 (UTC)

Why carbon-12?

I have a couple of questions about this line:

The choice of carbon-12 was made to minimise further divergence with prior literature.

In the first place, it doesn't explain how carbon-12 minimises divergence. My uninformed guess would have been that the value of the unified amu is about halfway between those of the chemistry amu and the physics amu.

In the second place, Holden Chemistry International (Jan–Feb 2004) pages 4–7 says:

Nier suggested to Mattauch that the ¹²C = 12 mass scale be adopted because of carbon's use as a secondary standard in mass spectrometry. Also, ¹²C = 12 implied acceptable relative changes in the atomic weight scale, i.e., 42 parts-per-million (ppm) compared to 275 ppm for the ¹⁶O = 16 scale (which would not [be] acceptable to chemists).

(I note that Holden's 275 ppm differs from the 282 ppm used in our article, but there I expect we are more accurate.) jnestorius^(talk) 12:21, 30 March 2017 (UTC)

I have actually seen an oxygen 16 periodic table. It was not new :-) People come up will all sorts of justifications, but the reality is that 1H, 12C, and 16O all work just fine. Standardization on something was and is more important than which one you choose in this case. Don't try to read to much into these decisions as if they were made by the scientific Justice League of Nations. AManWithNoPlan (talk) 13:12, 30 March 2017 (UTC)

I don't think your comment is of any help in explaining the sentence "The choice of carbon-12 was made to minimise further divergence with prior literature". jnestorius^(talk) 12:27, 31 March 2017 (UTC)

Your Holden quote suggests that the C12 scale is not "halfway between natural-O and O16, but rather very very close to natural O. So that's my guess. "Prior literature" really means "prior chemistry literature", i.e. "prior literature using the natural-O scale". And it minimizes divergence because natural-O happens to be 15.999/12 the mass of C12. Whereas O16 is significantly different, 15.995/12 the mass of C12. (See Oxygen-16.) Do you agree? I'm not an expert on this. --Steve (talk) 13:57, 31 March 2017 (UTC)

2018/2019 redefinition of the Dalton

With the official change of the kg, mole and other units in May 2019, the Dalton is being officially redefined as 1 kg/kmol (aka 1 g/mol) and the unified atomic mass unit is also being rendered obsolete. This article needs a rewrite to reflect the change and move the carbon-12 definition into the history section. Also, I think we need to revisit renaming the article to Dalton. Jasoninkid (talk) 18:57, 26 January 2019 (UTC)

The more I'm reading we need to hold of as it looks like the Dalton/amu may have got stuck in an ill-defined Netherland with the new redefinition.Jasoninkid (talk) 19:05, 26 January 2019 (UTC)

Did you see the section Atomic mass unit#Relationship to SI? It says that carbon-12 will continue to be the definition. There's a reference for that pointing to a quote from BIPM. Do you agree, or what do you think? I didn't write that section, and don't know what's correct. --Steve (talk) 22:57, 26 January 2019 (UTC)

No, carbon-12 is no longer a part of the definition. The SI-unit mol is defined through having a prescribed value of the Avogadro constant N_A as exactly 6.022 140 76 × 10²³ mol^–1 User:Saittam — Preceding undated comment added 13:24, 7 April 2021 (UTC)

References

Authoratative vs. Vernacular

There is a persistent problem with the authoritative and prevailing scientific definition, units, and language being deprecated by editors in favor of vernacular and use in preparatory texts. These less authoratative and professional uses should be accurately reflected but not take primacy over SI, IUPAC, and prevailing science.

a) example: Da being moved to a primary position in front of u, the official SI symbol for this unit. Da is specifically recognized and acceptable for use with the SI unit system as a synonym of u. This relationship is not accurately reflected in the current article, even as a footnote. This is misleading.

b) example: The use of amu as an abbreviation of the unified atomic mass unit is only prevalent in elementary school and some college texts. It is not particularly widely used in the primary scientific literature. The use of 'amu' as unit is even more unacceptable, although it does occur. The current version of the article states simply that this is "common", which is grossly misleading and ignores both the prevailing use in the scientific literature today and authoritative sources (e.g. IUPAC). --Nick Y. (talk) 14:53, 17 July 2019 (UTC)

I'm not convinced that your point (a) is correct in modern terms. The ninth SI brochure (and you do seem to prefer it, amongst others as an authoritative guide), for example, uses the dalton and its symbol Da exclusively in the main text and lists it (without the unified atomic mass unit) in Table 8: Non-SI units accepted for use with the SI Units. The unified atomic mass unit and is symbol u are listed only once, and then only in a footnote to this table. The inference is that the dalton is the primary unit accepted for use with the SI, and that the unified atomic mass unit is potentially no longer so, albeit being recognised as being the same unit (the SI would have erred if it had failed to mention it even if it is not considered "accepted for use with the SI", since that would have left its definition in an ambiguous state). My perception is that to call this "creeping vernacular" is inappropriate. Wikipedia should reflect current usage and science, not usage that predominated ten years ago. Even standards that have not been updated for several years reflect dated usage. Can you give recent authoritative examples that suggest the Da has not become the preferred term and symbol? —Quondum 22:07, 17 July 2019 (UTC)

Agreed. You have provided an authoritative source for the reversal of primacy of the Da over u. My point on creeping vernacular of 'amu' stands. the amu abbreviation is neither widely used nor is it authoritatively sanctioned. When it is used as an abbreviation it is also often used by the same source as a unit, which is particularly contrary to authoritative source recommendation and counter to prevailing scientific usage. --Nick Y. (talk) 21:15, 19 July 2019 (UTC)

Thanks for the response (and the edit). I strongly agree with your general point: that editors have a tendency edit in the "common view", which is all too often biased to what they have picked up at school or are familiar with as laymen, and that an encyclopaedia should reflect authoritative use within the discipline. The mention of the "amu" probably does not even belong in the lead, but I guess this will need someone who is prepared to research the history a bit to decide on its notability. This is also complicated by the semi-automatic abbreviation of "unified atom mass unit" to "atom mass unit". —Quondum 22:18, 19 July 2019 (UTC)

General Discussion: Page Name Change to "dalton (unit)"

I propose that the name of this page be changed to "dalton". This is consistent with other units, such as joule, meter, etc. The current page would become a redirect, as well as all the other similar variations. An acceptable alternative would be to change the name to "unified atomic mass unit"; however, "unified atomic mass unit" and its symbol "u" are much less commonly used yet similarly accepted by authoritative sources. Recently "dalton" has been preferred in authoritative definitions of units over "unified atomic mass unit". Importantly, the current page name "atomic mass unit" is not the name of any widely used or authoritatively sanctioned modern unit. I understand that "atomic mass unit" can also be interpreted generally as "units of mass used for atomic scale objects"; however, this is like naming the "joule" page as "energy unit". - Nick Y. (talk) 19:23, 22 October 2019 (UTC)

I am totally on board with this suggestion (I was just waiting for familiarity with the new SI to grow a bit before suggesting it myself). Just one suggestion, though: Dalton is a disambiguation page, and since the unit is arguably not a clear contender for primary topic, I would suggest renaming this article to dalton (unit) (currently a redirect to this article), consistent with foot (unit), hartley (unit), chain (unit), erlang (unit), gal (unit), gray (unit) and many more. —Quondum 19:41, 22 October 2019 (UTC)

The name "dalton (unit)" may be helpful or necessary. However, I disagree that it is not a contender for primary topic. I see no other more notable or significant uses of "dalton" (without an additional modifier). It thus passes relative notability easily. Examining the other examples: "Foot" has an obvious and more common usage. Same with "chain" and "gray" (although via variant spellings). "Hartley (unit)", "erlang (unit)", and "gal (unit)" are somewhat compelling examples for "dalton (unit)". They probably pass relative notability; although "Erlang (unit)" has software that may be more notable (I don't know). I doubt they pass on absolute notability. These examples are all more obscure than atomic mass units that essentially all primary schools teach in some form and is used extensively in multiple professions that collectively make up a substantial population. The best argument against the use of the simpler title "dalton" is clarity. Most users will likely search for "amu" or some such vernacular terminology when looking for this page. Dalton is likely a less familiar name for a commonly understood and clearly notable concept (nucleon-scale units of mass). However, it is different to say that macroscopic units of length are notable than to say that the meter is notable (both are obviously). I am fine with "dalton (unit)" based primarily on clarity. What is absolutely clear is that the current page name is grossly incorrect and leads to confusion rather than clarity. – Nick Y. (talk) 15:17, 23 October 2019 (UTC)

A quick follow up thought: The best option may be to redirect "dalton" to "dalton (unit)" and add a disambiguation link in the header. That way if someone searches for "dalton" they get what they are looking for in all probability (unless they are looking for the minor character from Buffy the Vampire Slayer television series, the Danish musical band, the non-playable main character in Chrono Trigger, the lunar crater, or chemistry software). It is inappropriate to direct everyone who searched for "dalton" to the disambiguation page when ~99% are looking for "dalton (unit)". For those searching for "amu" they will see "(unit)" and understand that they have arrived in the right place and understand that it is a unit immediately and still bring the clarity discussed in my previous comment. – Nick Y. (talk) 15:36, 23 October 2019 (UTC)

I am inclined to agree with you on every point. The current disambiguation page would be moved to Dalton (disambiguation). I like the clarity of "dalton (unit)", but I realize that many articles on units do not follow this pattern, making either "dalton (unit)" or "dalton" acceptable to me. —Quondum 19:57, 23 October 2019 (UTC)

Below I address the Wikipedia article title considerations Wikipedia's naming conventions regarding renaming "atomic mass unit" to "dalton (unit)":

Recognizability – Atomic mass unit is more recognizable to certain audiences (even if fails all other criteria). Daltons and Da/kDa are nonetheless quite recognizable and certainly more common in print. Although not of outstanding accuracy a google search results in 138M instances of "dalton" (some of which are regarding the unit's namesake) and 38M instances of "atomic mass unit" (many of which are historical). One analogy might be Mumbai vs. Bombay. Bombay is more recognizable in the English speaking world but Mumbai is also widely recognizable (and its modern official name and the Wikipedia namespace).

Naturalness – Dalton along with its symbol Da and variants such as kDa is certainly a more natural link from other articles as this is an actual unit that is attached to the molecular masses of chemicals and molecules. There is probably a more mixed usage in user search terms (addressed readily and transparently by redirect). (Bombay redirects to Mumbai).

Precision – Dalton (unit) is precise. It references a specific unit precisely defined consistently by multiple authoritative sources. Atomic mass unit is imprecisely defined with multiple contradicting definitions, and not accepted by any authoritative sources. There are few articles with a similar namespace. The addition of "(unit)" enhances naming precision and distinguishes it further from the minor Buffy the vampire slayer character.

Conciseness – "Dalton" is most concise. "Dalton (unit)" is both concise and clear. "Atomic mass unit" and "unified atomic mass unit" are less concise.

Consistency – Without exception, all other Wikipedia pages on units use officially sanctioned names for the unit, with particular deference to the International System of Units, IUPAC and IUPAP. Dalton (unit) is officially sanctioned and/or used by all three. The use of "Atomic mass unit" is specifically deprecated by these organizations. As with other units, the definitions and sometimes the names of the units have changed over history (some very recently). Historical definitions and names are contained within the main article which uses the current official name. The gravet does not have its own page.

– Nick Y. (talk) 19:54, 24 October 2019 (UTC)

Note that there is a related conversation above from nearly a decade ago. The crux of the consensus was that as long as the dalton is an "alternative" to the unified atomic mass unit the name should not be changed. Dalton is now the primary unit used by the current SI definitions and the unified atomic mass is a secondary note stating that it is equivalent and another name for the same unit. Bureau International des Poids et Mesures (2019): The International System of Units (SI), 9th edition, English version, page 134. Available at the BIPM website – Nick Y. (talk) 17:10, 25 October 2019 (UTC)

I'd suggest opening a new section to make specific rename proposal with a short summary of the motivation to poll the level of support over a window of a week or two – this section has the format of a general discussion, making it tricky to express a simple support/oppose position. You seem to be the proposer. I, for one, will support. —Quondum 18:54, 25 October 2019 (UTC)

Poll: Page Name Change to "dalton (unit)"

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: The article is moved per the excellent arguments of the proposer. However there is not consensus at this time to move the dab page. — Martin (MSGJ · talk) 21:50, 1 November 2019 (UTC) — Martin (MSGJ · talk) 21:50, 1 November 2019 (UTC)

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Atomic mass unit → Dalton (unit) – This is a proposal to make the following page move, redirect, and new page: Atomic mass unit → Dalton (unit) & Redirect dalton → Dalton (unit) & Add Dalton (disambiguation) The reasons are:

• "dalton (Da)" is now the primary unit name and symbol used by the International System of Units. See the universally authoritative text: Bureau International des Poids et Mesures (2019): The International System of Units (SI), 9th edition, English version, page 134. Available at the BIPM website "Unified atomic mass unit" and its symbol "u" (not to be confused with "atomic mass unit") is also acceptable and synonymous but is now mentioned secondarily.
• "Atomic mass unit" (Not to be confused with "unified atomic mass unit") is not a modern unit. It is not sanctioned by any authoritative sources. It is deprecated by nearly all sources, including standards bodies, scholarly journals, and publishers.
• "Atomic mass unit" is rarely used in the scientific literature. It is, however, used in some contexts such as some primary schools.
• "dalton" and "Da" is the prevailing and most common name and symbol for this unit. "unified atomic mass unit" (not to be confused with "atomic mass unit") with its symbol "u" is less commonly used but accepted by SI.
• "dalton" is consistent with other article titles on SI accepted units by using an official name of the unit as the title of the Wikipedia article. E.g. metre, gram
• "dalton (unit)" is consistent with the article titles of other units where the addition of "(unit)" adds precision and clarity. E.g. foot (unit).
• "dalton (unit)" is concise. It is much more concise than the SI accepted alternative "unified atomic mass unit".
• "dalton" and Da are correct units actually in modern use and thus make natural links. User search terms are likely mixed.
• "dalton" is widely recognizable. The long-ago deprecated "atomic mass unit" (not to be confused with the SI accepted "unified atomic mass unit") and its symbol "amu" remain familiar to certain lay populations.
• There are very few other minor uses of "dalton" without modifiers. Nonetheless, the addition of "(unit)" brings additional name precision and adds clarity.

– Proposed by Nick Y. (talk) 20:24, 25 October 2019 (UTC) Please support or oppose below and briefly state reason (add more extensive discussion in the section above):

• Support – As the proposer I obviously support. – Nick Y. (talk) 20:24, 25 October 2019 (UTC)
• Support – I agree with the given motivations, and it seems that every objection given in the previous rename proposal discussion above no longer holds. The changed position of SI listing the dalton as an accepted unit, and not the universal atomic mass unit, almost certainly reflects modern usage. —Quondum 22:56, 25 October 2019 (UTC)

• Support moving Atomic mass unit to Dalton (unit), but oppose changing the disambiguation status of Dalton, which is a highly ambiguous term with numerous meanings unrelated to the unit. bd2412 T 21:08, 1 November 2019 (UTC)
• Unsure about moving AMU to Dalton (unit), but Dalton itself should remain the disambiguation page in all cases. Headbomb {t · c · p · b} 21:33, 1 November 2019 (UTC)

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The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

M(r) to Dalton

Some older papers use M(r), I think molar mass, relative. Can this wikipedia main page explain how to convert M(r) to Dalton? Is it 1:1? It's hard to search for this. 2A02:8388:1602:6D80:3AD5:47FF:FE18:CC7F (talk) 19:32, 13 May 2021 (UTC)

Plural

What is the plural of Dalton? Daltons? 5000 Daltons for a protein? Or 5000 Dalton instead? The main article should clarify that IMO. Right now I will stick with the singular but perhaps I am wrong. 2A02:8388:1602:6D80:3AD5:47FF:FE18:CC7F (talk) 16:45, 15 May 2021 (UTC)

Daltons (in lowercase when it doesn't start a sentence), much like newtons, pascals, etc... This is covered by the basic rules of grammar and doesn't need to be featured in an article about the topic. Headbomb {t · c · p · b} 18:03, 15 May 2021 (UTC)

At rest

The article begins, "The dalton... is a... unit of mass defined as 1/12 of the mass of a[n]... atom of carbon-12 in its nuclear and electronic ground state and at rest." ("At rest" refers to invariant mass aka rest mass.) I think "at rest" is unnecessary, because "relativistic mass" is a fiction: mass stays the same, it's just that there is the Lorentz factor γ = 1/(1 – v²/c²)^1/2, c = speed of light. Solomonfromfinland (talk) 13:15, 17 July 2023 (UTC)

Wikicode

I edited this article for concision. One thing i did, was, for superscript, replacing the wikicode "" with the more concise "{{sup|}}". Likewise for subscript. Okay? Solomonfromfinland (talk) 13:32, 17 July 2023 (UTC)

Da is not equal to g/mol

The following refers back to a discussion in May 2007 of "Daltons vs g/mol" by Roddyboy and others.

The statement "Da = g/mol" occurs often in chemistry texts and elsewhere. Since the LHS has the dimension of mass and the RHS has the dimension of mass/amount, it is, of course, incorrect. This misconception comes about because of the missing atomic-scale unit for amount, namely one entity, symbol ent. The number of entities in a sample of a substance X is given by N(X), which is easily understood. The corresponding amount of the substance is given by n(X), which is an aggregate of N(X) entities:

n(X) = N(X) ent

where ent represents the smallest possible amount of any substance and is the appropriate atomic-scale unit for amount (hence the space before the symbol)—and has the dimension of amount. This aggregate is also easily comprehended. The SI writes this relationship between amount and number of entities as:

n(X) = N(X)(1/N_A)

where N_A is a "universal" (i.e. independent-of-the-substance) dimensional constant known as the Avogadro constant (not to be confused with the Avogadro number, which is the number of entities in one mole). In other words, the SI would have us believe that the amount (of a substance) is an aggregate of N(X) reciprocal-Avogadro-constants. As has been well documented, this definition of amount is universally misunderstood. And is the main reason why amount and its symbol, n(X), are studiously avoided in chemistry textbooks, which refer, instead, to "number of moles" (often along with "number of grams" in place of mass), or sometimes just "moles of" and "grams of". This (in my opinion) is pedagogically irresponsible! This is equivalent to physics texts referring to length as "metres of" or time as "seconds of" or electric charge as "coulombs of". [Not to mention that the gram is not the base unit of mass.]

The dimension of N_A is "reciprocal amount", whatever that means. Many students (and, judging by current textbooks, some of their teachers) do not have a good concept of N_A, often confusing it with (or even equating it to) the (dimensionless) Avogadro number. In fact, it is simply the number one per entity (exactly), N_A = 1/ent. And since a mole is (now, exactly) 6.022 14076 x 10²³ ent, the Avogadro constant is (exactly) the number 6.022 14076 x 10²³ per mole—sometimes confusingly described as 6.022 14076 x 10²³ "reciprocal moles", whatever that means, whereas the Avogadro number is exactly (the number) 6.022 14076 x 10²³.

The so-called molar mass of the substance, M(X), is defined as the amount-specific mass:

M(X) = m(X)/n(X) = [N(X)m_av(X)]/[N(X) ent] = m_av(X)/ent

where m_av(X) is the sample-average entity mass, written as A_r(X) Da, where the relative atomic-scale mass, A_r(X), can be found from catalogues such as the Periodic Table. Thus:

M(X) = A_r(X) Da/ent

where Da/ent, dalton per entity, is the appropriate atomic-scale unit for molar mass. [In the SI, we find this written as DaN_A, a difficult-to-comprehend product of the well-defined atomic-scale mass unit and the mysterious (and very poorly understood) Avogadro constant.]

Since one mole is given by:

mol = 6.02214076 x 10²³ ent

and one gram is (for all practical purposes—to within an order of 10^–10) given by:

g = 6.02214076 x 10²³ Da

we see that it is dalton per entity, Da/ent, that is (for all practical purposes) equal to gram per mole (or kilogram per kilomole):

Da/ent = g/mol = kg/kmol

So, for the molar mass, we (should) have (for all practical purposes):

M(X) = A_r(X) Da/ent = A_r(X) g/mol = A_r(X) kg/kmol

It is clear from this why the dalton should have been redefined, along with the mole, so that it is exactly related to the (redefined) fixed-h kilogram:

"Da = (1/6.02214076 x 10²⁶) kg, exactly"

In which case, the molar mass constant would be exactly 1 g/mol = 1 kg/kmol. If necessary, the "unified atomic mass unit", u, could be decoupled from the (exact) dalton and retained by its definition in terms of the (inexactly known in terms of the fixed-h kilogram) carbon-12 atomic mass.

And, in case anyone was wondering, the poorly understood Avogadro constant, N_A (not to be confused with the Avogadro number) is otherwise irrelevant!

[Over the past couple of decades or so, I have formally proposed introducing ent as the atomic-scale unit of amount (to be accepted for use with the SI) and redefining the atomic-scale unit of mass, dalton, exactly in terms of the (now redefined) fixed-h kilogram a number of times in published papers, but (so far) to no avail, in either case.]

In summary, it is important here to avoid the false claim that "Da = g/mol", often seen in chemistry texts and online tutorials. Fortunately, so far, in this article on the atomic-scale mass unit, dalton, this has indeed been avoided.

Boppennoppy (talk) 22:21, 14 November 2024 (UTC)