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Atomic Weight Not So Constant

kdawson posted more than 3 years ago | from the thulium-and-thalium dept.

Science 147

DangerousBeauty writes "Yahoo has a Canadian Press story up about new changes to the periodic table of elements concerning the weights of specific elements — it seems that the weights fluctuate based on where they are found in nature. Quoting: '"People are probably comfortable with having a single value for the atomic weight, but that is not the reality for our natural world," says University of Calgary associate professor Michael Wieser.' He is is secretary of the International Union of Pure and Applied Chemistry's Commission on Isotopic Abundances and Weights."

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147 comments

Anonymous Coward (-1)

Anonymous Coward | more than 3 years ago | (#34558616)

So that's what's up with my weight around Christmas, my atoms are fluctuating.

You know the cliché (2, Funny)

Anonymous Coward | more than 3 years ago | (#34558626)

American atoms are fat.

Re:You know the cliché (-1, Offtopic)

fyngyrz (762201) | more than 3 years ago | (#34558866)

European atoms don't shave their legs or pits. Or use deodorant.

You've got nothing on American clichés, you silly euro-cule.

Re:You know the cliché (-1, Offtopic)

Yvanhoe (564877) | more than 3 years ago | (#34559070)

Yeah, you are totally right, it is not a cliché, it is a fact : http://www.nationmaster.com/graph/hea_obe-health-obesity [nationmaster.com]

Re:You know the cliché (-1, Offtopic)

znerk (1162519) | more than 3 years ago | (#34559626)

Yeah, you are totally right, it is not a cliché, it is a fact : http://www.nationmaster.com/graph/hea_obe-health-obesity [nationmaster.com]

The Guardian [guardian.co.uk] says you Euro guys are fatter than those American guys. Got any other retarded copypasta you wanna spew?

Re:You know the cliché (0)

Yvanhoe (564877) | more than 3 years ago | (#34559788)

Yeah...
http://www.iaso.org/site_media/uploads/Global_Prevalence_of_Adult_ObesityMay__2010_revised_with_headings.pdf [iaso.org]
(from the association quoted by the Guardian article)
The only stat that is lower than average in US by EU standards is, surprisingly, the one of males less than 30. The one that is suprisingly high is the number of obese women of more than 30 years. I guess that is why there are so "yo mama" jokes on the other side of the Atlantic... As the article pointed, you can find some categories in some states that have higher rates than the US taken as a whole. But overall, the picture stays pretty clear...

Re:You know the cliché (0)

c6gunner (950153) | more than 3 years ago | (#34560554)

Well, first of all, you're completely misreading the stats. There is no breakdown by years. The numbers at the top indicated the BMI percentage, not the age.

So, with that in mind, looking at the stats tells us that the US has the highest percentage of males with a 30+% BMI. On the other hand, MANY European nations have a higher percentage of males who are obese, but under the 30% mark. What that seems to indicate is that they have a roughly equivalent prevalence of overall male obesity, but fat men in the US tend to be fatter.

The situation with women seems similar, although Albania actually beats out the US for the "monstrous" category, and the gap tends to be a bit smaller.

Getting a clear picture isn't possible from those stats without doing some number crunching and/or creating a few graphs. I would have taken a shot at it if it were possible to just copy-paste the data into a spreadsheet, but the formatting of that PDF is pretty horrible. Also, they seems to think that Israel and Turkey (amongst other questionable choices) are part of Europe, so some reorganization of their data would be necessary in order to get a valid comparison between Europe and the US.

Re:You know the cliché (1)

Yvanhoe (564877) | more than 3 years ago | (#34561512)

Hehe, oops, I indeed misread the first line.
If the definition of obesity is simply "more than 30 of BMI", USA really wins the contest in the males category.
If you consider the definition to be 25 or more (what the table calls "overweight"), the gap is closer but neither Germany nor Greece mentioned in the article manages to top the 72% of overweight of USA. The only way for them to do so is to compare the 25-29.5 category while dismissing the 30+, which is a kind of silly way to measure don't you think ?
Albania is a small country with a small population. If we broke down US to units of the same size it would not be difficult to find a comparably catastrophic situation.

By the way, I must point out that I was responding to a sarcastic trollish comment in order to amusingly feed a troll, not on a very serious tone. Suggesting that the obesity rate is a valid measure of a country's value is a bit ridiculous. There are obviously more objective was to do so. Like the number of cheese varieties produced....

Re:You know the cliché (0)

Anonymous Coward | more than 3 years ago | (#34560562)

How about...
http://calorielab.com/news/2010/06/28/fattest-states-2010/ [calorielab.com]
Notice how *NONE* of the states even get to the 32% number you are throwing around? It just is not numerically possible for it to happen.

Stats can be made to dance on a head of a pin. Also notice in *NEITHER* one of those do they state what is 'fat' or 'obese'. Just a magic number. They seem to usually gloss over the methodology. For good reason too. Even on that site they are all over the place in the numbers. People throw out numbers to impress each other.

I have seen numbers anywhere from 19% to 48%. *EACH* and every one had different methods for stating what was fat. What is the variance? What is the sample population? What is the value for each category? How did they find out this information? Was it phone calls? Doctor visits? What are the known issues with the methodology? For example if you are skinny and healthy in America would you bother going to a doctor? Yet in another country it may be customary to do so every 6 months? What was the age rates? Are they picking mean or average? Are they comparing a population of 300+ million to a population of 4 million (btw yes), apples and oranges?

Also for example I would be considered 'fat' by many of these charts ('only 15 over') and I bet you would be also (it doesnt take much only ~15 pounds over the 'normal rate' in many cases). Yet no one says 'omg your huge' or 'you should loose 20 pounds'. Most actually say the opposite. In America we have a very diverse population. Many have come here and are eating very high carb diets compared to what their grandparents ate 100 years ago. It is just not in their genetic makeup to burn those off. Also many of the high carb diets are cheaper in price. They also taste much better. So you have a vicious cycle of both cheap and tastes good. We also have a 'baby boomer' population so we have a slight skew to an older population.

Just because you are 'skinny now' and live in a country where others are 'skinny'. Does not mean it can not happen to you. I would be willing to *BET* cash you are in your 20s early 30s. The midlife plump up hasnt happened to you yet. It happens to everyone (esp to those of European decent). You then have to figure out how to change your whole diet. Bad carbs are everywhere.

I was like you at one point. I could eat whatever I liked and not gain a pound. I would look at overweight people and go 'what is wrong with you just dont eat as much'. Your life will change when you get near 40. If you dont think so you are deluding yourself. My elders told me the same thing. I laughed at them. Its true... Now back to my 20 year old weight :)

Also I question why you posted what you did. Here is a bit of homework for you. Perhaps you are looking for *ANYTHING* in which you can pick on 'those Americans' with? Perhaps you feel inadequate in some way? So you latched on to 'Those Americans are fat' 'nunh huh yes they are and here are my stats to back it up'. You may want to re-examine your motives in posting like that?

http://en.wikipedia.org/wiki/Illusory_superiority [wikipedia.org]
http://en.wikipedia.org/wiki/Bandwagon_effect [wikipedia.org]
http://en.wikipedia.org/wiki/Bias_blind_spot [wikipedia.org]
http://en.wikipedia.org/wiki/Confirmation_bias [wikipedia.org]
http://en.wikipedia.org/wiki/Negativity_bias [wikipedia.org]
http://en.wikipedia.org/wiki/Attentional_bias [wikipedia.org]
http://en.wikipedia.org/wiki/Observer-expectancy_effect [wikipedia.org]
http://en.wikipedia.org/wiki/Overconfidence_effect [wikipedia.org]
http://en.wikipedia.org/wiki/Stereotyping [wikipedia.org]
http://en.wikipedia.org/wiki/Actor%E2%80%93observer_bias [wikipedia.org]

Re:You know the cliché (0)

Anonymous Coward | more than 3 years ago | (#34559110)

one day we'll learn that just because we can afford to by food because all of our income doesn't go to the government to pay some lazy 45 year old's retirement, doesn't mean we should.... we should be saving it to bail out Europe's failed economies....

Re:You know the cliché (1)

NoSleepDemon (1521253) | more than 3 years ago | (#34559616)

Shouldn't you be saving that for yourself when you need the heart bypass your country will refuse to pay for?

Actual Link to Document (5, Informative)

Fluffeh (1273756) | more than 3 years ago | (#34558632)

Link to actual article is:
link [iupac.org]

Re:Actual Link to Document (5, Informative)

chichilalescu (1647065) | more than 3 years ago | (#34558700)

Yes. thank you for that link. Anybody with minimal knowledge of how atomic weights are computed (i.e. a weighted average of the atomic masses of the various isotopes) can guess that if the concentrations of isotopes are different in different samples, the "atomic weight" will be different.
I went and read the famous abstract anyway. quote: "This fundamental change in the presentation of the atomic weights represents an important advance in our knowledge of the natural world and underscores the significance and contributions of chemistry to the well-being of humankind in the International Year of Chemistry 2011."
This article is just about the results of some measurements. ok, useful measurements, but NOT an important advance in our knowledge of the natural world.

Re:Actual Link to Document (1)

JustOK (667959) | more than 3 years ago | (#34558712)

the value of the findings vary depending on the observer.

Re:Actual Link to Document (0, Troll)

Anonymous Coward | more than 3 years ago | (#34560608)

no they don't

Re:Actual Link to Document (0)

Anonymous Coward | more than 3 years ago | (#34558896)

nothing new here, it was know from ages that isotopes have a different weight.

nothing is changing, especially not the atomic weight of atoms.

their value is revised, but the value all by itself is as constant as it ever was.

Re:Actual Link to Document (0)

Anonymous Coward | more than 3 years ago | (#34560198)

The rest of us just read KDawson and figured it to be shit story
Everyone with a couple of brain cells figured the article was trying to say (rather crudely to the point of BS) that the ratio of different isotopes for a couple of elements has been refined resulting in a minor change to a few average numbers

Re:Actual Link to Document (1)

Magic5Ball (188725) | more than 3 years ago | (#34560266)

The important advance is in the presentation of weighted atomic masses as ranges with context, rather than the wet chemistry behind the changed numbers. At the very least, presenting a range of masses reminds us to think about the sources of the atoms analysed and variations in their collective attributes.

Re:Actual Link to Document (2)

NeverVotedBush (1041088) | more than 3 years ago | (#34560648)

And it really isn't even news. The fact that isotope ratios vary (and thus average atomic weight/mass) depending on the source/location is fundamental to things like carbon dating.

Atomic weights based on accepted isotope distributions have always been somewhat approximate. That accepted weights would be revised should have been expected.

Re:Actual Link to Document (1)

Rich0 (548339) | more than 3 years ago | (#34561262)

Yup - this is also one of the reasons why the mass of a liter of water/etc was avoided as the basis for the kilogram. It is almost impossible to obtain water of any particular isotopic composition, and it varies around the world. Water is also non-ideal for other reasons as well which I won't get into...

Re:Actual Link to Document (5, Informative)

Interoperable (1651953) | more than 3 years ago | (#34559092)

Thanks. The article makes it clear that the major change here is that the way in which atomic weights will be presented is changing. It's not just that they're being updated to reflect a more complete measurement, it's that atomic weights will now be represented as a range of possible values rather than a single value. It's not every day that the way in which information is presented in the periodic table changes.

Re:Actual Link to Document (1)

ari_j (90255) | more than 3 years ago | (#34561490)

Actually, from the Slashdot front page you can tell everything you need to know about the differences between the article and the summary: It was posted by kdawson, and therefore the differences are fundamental in nature.

Re:Actual Link to Document (2, Informative)

Anonymous Coward | more than 3 years ago | (#34562254)

But the range of possible values for the atomic weight is already represented by the number of decimal places displayed. For example, compare the the number of decimal places for F (18.9984032) and Pb (207.2).

strange brew that's also good for you (-1)

Anonymous Coward | more than 3 years ago | (#34558636)

That would be home made Kombucha. It's both atomically & cosmically 'correct', although cosmetically, it lives alone.

Natural constants? (0)

boredgeestje (756712) | more than 3 years ago | (#34558650)

I don't think there are any constants in nature. We humans just like to perceive them as such, so it makes our calculations a whole lot easier.

Re:Natural constants? (1)

nschubach (922175) | more than 3 years ago | (#34558876)

*cough* speed of light/red shift *cough*

(I know it's not apparent, but I'm not disagreeing... but I'm totally expecting to be jumped by a million and a half people claiming how ignorant I am for defying conventional physics theory.)

Re:Natural constants? (1)

mattr (78516) | more than 3 years ago | (#34559032)

Okay yes constants, but as you know this is only known really well for our light cone and epoch, and even then many caveats.. speed of light changes when traveling through different substances / states of matter. Red shift changes depending on gravitational potential relative to the source, or to expanding spacetime, etc. as wikipedia tells us..

Re:Natural constants? (0)

Anonymous Coward | more than 3 years ago | (#34559598)

speed of light changes when traveling through different substances / states of matter

No shit, Dr. Snell. How about "speed of light in a vacuum"?

Red shift changes depending on gravitational potential relative to the source, or to expanding spacetime, etc. as wikipedia tells us..

Red shift *is* about expanded spacetime. Study some more, kid.

Re:Natural constants? (1)

Shining Celebi (853093) | more than 3 years ago | (#34560286)

No shit, Dr. Snell. How about "speed of light in a vacuum"?

Where can I find a perfect vacuum? Nowhere. So never in the universe is light traveling at exactly c - there are always tiny variations. So yeah, in practice, it's not really a constant.

Re:Natural constants? (1)

NeverVotedBush (1041088) | more than 3 years ago | (#34560684)

Actually you are wrong. Even though there may be an atom or molecule or few floating around in some chamber, a photon doesn't have to hit it. As far as the photon is concerned, if it doesn't hit anything, it was a perfect vacuum.

Re:Natural constants? (2)

andrewagill (700624) | more than 3 years ago | (#34560902)

Huh. Your argument is well-reasoned and compelling. I guess I'll have to go back to the permittivity and permeability of free space (the product of which is the inverse of the square of the speed of light in a vacuum), Coulomb's constant, the gravitational constant, the Stefan-Boltzmann constant, Planck's constant...

Re:Natural constants? (1)

Tyler Durden (136036) | more than 3 years ago | (#34561310)

Photons, like any other massless particle, always travel at exactly c. It is a constant.

Re:Natural constants? (1)

digitig (1056110) | more than 3 years ago | (#34559188)

Well, we take the speed of light to be constant because any other explanation of our present observations fails Occam's razor. But Occam's razor doesn't necessarily tell us what is the case, it tells us what the most practical working hypothesis is likely to be. In other words, we choose the simplest explanation because it makes the calculations easier (and we have no reason to complicate them).

Re:Natural constants? (0)

Anonymous Coward | more than 3 years ago | (#34559138)

TFA isn't even about constants. It's about ratios of isotopes. There's no reason to assume that those are constant in any way. It's nothing new, and the summary is needlessly sensationalist, which is also nothing new.

Re:Natural constants? (5, Insightful)

vlm (69642) | more than 3 years ago | (#34559178)

I don't think there are any constants in nature.
We humans just like to perceive them as such, so it makes our calculations a whole lot easier.

Also, those same calculations show that some things, like proton mass, speed of light, gravitational constant, a couple others, have to have remained constant within a very large number of decimal places in order for old stuff to have changed the same way new stuff changes. More decimal places that we usually have sig figs to measure stuff, so by sig figs rules, have to treat them as constant, its not just an "easier" thing.

For your average chemical engineer bucket chemist, small changes in atomic weight are going to be statistical noise.

Re:Natural constants? (1)

flintmecha (1134937) | more than 3 years ago | (#34561224)

I don't think there are any constants in nature.

Pi would like a word with you.

Re:Natural constants? (0)

Anonymous Coward | more than 3 years ago | (#34561656)

If you're not talking about the mathematical constant, then pi - the ratio of circumference to diameter - varies [wikipedia.org] . General relativity asserts that the space we live in isn't flat, so pi (the natural one), isn't necessarily the same as Pi (the true one). Avoiding an explanation of curved space-time, you can see this in a curved 2D-space (technically a manifold), like the surface of the Earth. pi for a small circle centered close to the North pole is equal to Pi. However, pi for a circle centered on the North pole, but whose circumference is the equator, has a value of 2!

I don't get it (3, Insightful)

FTWinston (1332785) | more than 3 years ago | (#34558656)

Isotopes exist, right. And by definition, different isotopes of the same element have different mass. I'd take it as a given that the distribution of certain isotopes are different in different places.

But what is this article actually saying? The atomic mass number is meant to be the universal average ... now they may have got that slightly wrong, but why exactly do we need a range of universal averages for each isotope? That's surely some sort of misnomer.

Re:I don't get it (5, Informative)

Sockatume (732728) | more than 3 years ago | (#34558682)

They're recalculating the average atomic weight, the one on the periodic table, based on the abundances of the different isotopes in nature. If you're trying to calculate the mass of, say, 300,000 molecules of something, you use the average atomic weight and don't try to figure out what isotope each atom is.

Re:I don't get it (0)

Anonymous Coward | more than 3 years ago | (#34559404)

"They're recalculating the average atomic weight, the one on the periodic table, based on the abundances of the different isotopes in nature." But surely this varies in nature? Are they calculating an average for the planet earth, for the solar system, for the entire universe or for their own lab ?

Re:I don't get it (0)

ChipMonk (711367) | more than 3 years ago | (#34559596)

So you're saying they're using the atomic weight of some hypothetical "typical" atom, even though that "typical" atom never actually, you know, occurs in nature.

Re:I don't get it (2)

SimonTheSoundMan (1012395) | more than 3 years ago | (#34558702)

What I do not get is, of course weight will be different in nature. Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.

I think these chemists mean 'atomic mass'? I'm an engineer so correct me if I'm wrong.

Re:I don't get it (4, Informative)

Marcika (1003625) | more than 3 years ago | (#34558792)

What I do not get is, of course weight will be different in nature. Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.

I think these chemists mean 'atomic mass'? I'm an engineer so correct me if I'm wrong.

Atomic weight is a dimensionless quantity (ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12).

I think the convention in chemistry is to call the absolute mass of an isotope (in kg or whatever) "atomic mass", and to call its relative mass (dimensionless) "atomic weight".

Re:I don't get it (5, Informative)

PeterKraus (1244558) | more than 3 years ago | (#34558938)

Atomic mass is the precise mass of a given isotope, in AMU (symbol u) or Daltons (Da), where 1u = 1Da = 1/12 of a mass of one C12 atom.

Atomic weight, or relative atomic mass, is the abundancy-weighted average of atomic masses of isotopes. I'm not sure about the unit, but I guess using u or Da might not be to far off.

For general purposes we use molar mass (or specifically relative molar mass), which is the mass of a mole of atoms (or molecules or whatever). In case of atoms, it's the atomic weight times avogadro constant. Unit g/mol, (the biochemists tend to use Daltons, 1 Da = 1g/mol, confuzzlingly enough).

IAACh, but I'd guess the folk in IUPAC would get it right, so if I'm contradicting them, I'm wrong.

Re:I don't get it (1)

jo_ham (604554) | more than 3 years ago | (#34559048)

Well, IUPAC can't be right all the time - they standardised on "Sulfur" for goodness sake! ;)

I just got used to hydrogen being 1.0079, now I'm going to have to memorise the table all over again.

Re:I don't get it (1)

PeterKraus (1244558) | more than 3 years ago | (#34559520)

they standardised on "Sulfur".

What's that? :P

(Makes you wonder why there's no fenolfthalein either, eh?)

Re:I don't get it (0)

Anonymous Coward | more than 3 years ago | (#34562238)

In case of atoms, it's the atomic weight times avogadro constant. Unit g/mol, (the biochemists tend to use Daltons, 1 Da = 1g/mol, confuzzlingly enough).

Not quite: u and Da are units for the mass of one atom or one molecule, which is what you meassure in mass spectrometry. g/mol is the unit for the mass of an aggregate of atoms or molecules, and uses the weighted averages of the isotopic masses. IIUC from the other comments (yeah, like I would read the article), the update would affect the molar mass, measured in g/mol, and not the molecular or atomic masses, measured in u.

Re:I don't get it (2)

Lloyd_Bryant (73136) | more than 3 years ago | (#34558958)

What I do not get is, of course weight will be different in nature. Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.

I think these chemists mean 'atomic mass'? I'm an engineer so correct me if I'm wrong.

You aren't alone in that opinion - there is some controversy [wikipedia.org] over the name, simply because it is *not* a "weight" in any sense of the word.

The most popular suggested replacement is "relative atomic mass" (the base unit is 1/12 the mass of a carbon 12 atom), but even that is somewhat misleading since it's actually intended to be relative to the average atomic mass of a sample of the element as found "in nature".

The change is a result of them realizing that that there is actually some variation in the proportions of the different isotopes in samples found "in nature", so instead of a single fixed value, it requires a range that the average should fall in, based on observed variations in those proportions.

Re:I don't get it (1)

vlm (69642) | more than 3 years ago | (#34559210)

Weight is dependant on acceleration due to gravity and mass. An atom would weigh more on Earth than it would on the moon.

Not relevant. Theres nothing chemists love more than STP standard temperature and pressure. Extending that to "we're going to define all our weights as being in a 9.81 m/s2 grav field" is to be expected from that crowd (which I was/are almost a part of)

Wait until you learn about the various gas laws, and start posting to slashdot that they are all wrong because a mole of gas "on the moon" would take up a heck of a lot more than 22.4 liters.

Re:I don't get it (1)

PrinceAshitaka (562972) | more than 3 years ago | (#34559322)

This isn't news, we have known for a long time that there are different isotope ratios from different sources. This basically means that the atomic weight of say carbon, when looking really closely, is sample dependant, meaning different samples will have differing atomic weights because they have differing ratios of isotopes.

Re:I don't get it (1)

FTWinston (1332785) | more than 3 years ago | (#34559326)

Yeah, that was my interpretation also.

Re:I don't get it (1)

LWATCDR (28044) | more than 3 years ago | (#34560462)

Well from reading the link what I am getting is that they are changing how it is listed and calculated. It does make sense in away since the variablity in atomic weight of hydrogen is much higher than say uranium when looking at it as a percentages. So they are going to show Hydrogen as a range instead of a fixed number.

Isotopes (4, Insightful)

MichaelSmith (789609) | more than 3 years ago | (#34558658)

Atomic weight is calculated based on the number of isotopes of any given element. A handful have only one isotope and therefore a stable atomic weight, but most elements have more than one isotope, carbon 12, 13 or 14, for example.

Makes much more sense than weights fluctuate based on where they are found in nature. Its why centrifuges can be used to separate uranium 235 from uranium 238.

Re:Isotopes (1)

The_mad_linguist (1019680) | more than 3 years ago | (#34558954)

weights fluctuate based on where they are found in nature

But it's the truth. When we discovered some silicon on the moon, man, did that have a different weight.

Re:Isotopes (2)

aliquis (678370) | more than 3 years ago | (#34560194)

Next up on Brainiac:

Silicone breast, will they float or will they sink?

And are they really the best thing to grab hold of in case of office flood thanks to global warming?

Re:Isotopes (1)

smellsofbikes (890263) | more than 3 years ago | (#34561968)

Next up on Brainiac:

Silicone breast, will they float or will they sink?

And are they really the best thing to grab hold of in case of office flood thanks to global warming?

Well, for the record, silicone is typically slightly denser than water [answers.com] so that'd make for a less-than-excellent flotation device.

And, as a strange aside, newly-filled saline implants sometimes have a bit of air in them, and they can audibly slosh, which is a bit weird.

Atomic Weights were never constant (5, Insightful)

bhaak1 (219906) | more than 3 years ago | (#34558666)

The Atomic Weight is only an average of the isotopes found in nature divided by some constant mass unit.

How could they be constant if "they vary from sample to sample" [wikipedia.org] as even Wikipedia knows?

Somebody seemed to have failed his physics or chemistry classes.

Re:Atomic Weights were never constant (0)

Anonymous Coward | more than 3 years ago | (#34558772)

it seems somone has failed his grammar class :)

Re:Atomic Weights were never constant (0)

Anonymous Coward | more than 3 years ago | (#34558888)

More like someone does not understand the ideas and issues associated with sampling distributions. Statistics are a bitch....

Re:Atomic Weights were never constant (2)

ciderbrew (1860166) | more than 3 years ago | (#34559664)

Is the level of bitch a constant?

Re:Atomic Weights were never constant (1)

TeethWhitener (1625259) | more than 3 years ago | (#34560896)

Somebody seemed to have failed his physics or chemistry classes

That's a little harsh. Yes, it's been known for quite some time that average atomic weights vary from sample to sample, and the information content of the paper may not seem fundamentally novel. However, this is a paper where scientists are recommending a change in IUPAC's policy. For these standards boards, this is a fundamental issue. Think of it as similar to the "Pluto is/isn't a planet" debate. It seems like it's just semantics they're arguing (and I'm inclined to think that, in either case, it is. Funny story: I had to correct some kid in a museum recently because he was telling his little brother that Pluto no longer existed.), but passions can still become pretty inflamed.

Anyway, just thought I'd try to put the whole thing in perspective.

Meh (3, Insightful)

Zironic (1112127) | more than 3 years ago | (#34558668)

Looking at the title of the story I thought it would be something funky, but the entire story is just that they want to make the periodic table slightly more accurate for atoms that have isotopes. Everyone that has gone through high school chemistry should already know that that for unstable elements the table reference is an average at best.

This story is basically "ZOMG, it turns out that the weight of my mac and cheese isn't constant because the ratio of cheese to mac can vary!!!"

Re:Meh (0)

Anonymous Coward | more than 3 years ago | (#34558898)

So instead of just knowing that the atomic weight is the average of isotopes, the range will be listed?

How is this going to really change anything, except to make learning atomic weights more cumbersome? I can't think of a single situation where it will be more useful for me to know, for example, the range of carbon weights vs just knowing what each isotope's actual average weight is (and if I really needed to, could just look up the range).

What a useless exercise in making chemistry inaccessible to the non-initiated.

Re:Meh (1)

jo_ham (604554) | more than 3 years ago | (#34559076)

Not just unstable elements. Plenty of stable elements have more than one, sometimes multiple isotopes. boron, chlorine, bromine, tin to name just a couple off the top of my head.

Re:Meh (0)

Anonymous Coward | more than 3 years ago | (#34559480)

They're giving the error in the value. It's not funky, but you're downplaying it a bit much.

Masses not changing; only ratio of isotopes. (4, Informative)

Anonymous Coward | more than 3 years ago | (#34558680)

The scientific paper can be found here [doi.org] .

In Section 1.1 the weight is defined as the weighted mean over all the isotopes. Caesium 135 still has atomic mass 134.9059770(11) and caesium 137 still has mass 136.9070895(5); the way in which the relative abundances of isotopes is measured - that is all.

Sensationalist, slow news day (0)

Anonymous Coward | more than 3 years ago | (#34558706)

This is absolutely to be expected, but the title brings visions of detectable changes in mass of a particular isotope, which would be earth shattering.

Not surprising (1)

srussia (884021) | more than 3 years ago | (#34558746)

Given that the relative abundance of isotopes is quite variable, you might say that this development was periodictable.

Acronym of union (1)

skywatcher2501 (1608209) | more than 3 years ago | (#34558796)

Wait let me guess.. IUPACHCIAW, right??

Re:Acronym of union (-1)

Anonymous Coward | more than 3 years ago | (#34559220)

CIUPACHABRA

mass vs weight (0)

spoonist (32012) | more than 3 years ago | (#34558820)

Well duh [wikipedia.org] .

Why not look in Wikipedia first? (1)

astrobotanic (887574) | more than 3 years ago | (#34558860)

The IUPAC definition[1] of atomic weight is: An atomic weight (relative atomic mass) of an element from a specified source is the ratio of the average mass per atom of the element to 1/12 of the mass of an atom of 12C. The definition deliberately specifies "An atomic weight...", as an element will have different atomic weights depending on the source. For example, boron from Turkey has a lower atomic weight than boron from California, because of its different isotopic composition.[6][7] Nevertheless, given the cost and difficulty of isotope analysis, it is usual to use the tabulated values of standard atomic weights which are ubiquitous in chemical laboratories. http://en.wikipedia.org/wiki/Atomic_weight [wikipedia.org]

Useful info for Mars terraformers (0)

captainpanic (1173915) | more than 3 years ago | (#34559134)

But other than some intergalactic engineers, and of course astronomers, I don't think that any engineer will care. The earth was so properly blended when it was made that it's safe to assume that the isotope mixtures are a constant.

Re:Useful info for Mars terraformers (0)

Anonymous Coward | more than 3 years ago | (#34559186)

That doesn't make sense at all. There are huge variations in the chemical composition of the earth's crust depending on where you are. Some areas have a lot more gold, uranium, etc. than other places. Why would the same not be true to a much lesser degree of isotopes?

We know that isotopes vary in the atmosphere, for example, based on solar radiation, which is why you need to make corrections in radiocarbon dating. We use isotope variations to gather data from ice cores. Isotope ratios of elements that are (or have been) near radioactive sources will be different.

The whole point of the article is that isotope ratios is not constant because of local variations, and we've reached the point in measurement capabilities where the differences matter.

Wrong assumption (2)

Arrepiadd (688829) | more than 3 years ago | (#34559226)

The earth was so properly blended when it was made that it's safe to assume that the isotope mixtures are a constant.

Your assumption is actually wrong and that's why the values are updated. For instance, if you get a metal, from different mines around the world, the relative abundances of each of the isotopes vary slightly and this leads to different atomic weights for the same metal. This is why the atomic weights are updated. You can read about it in wikipedia [wikipedia.org] .

Indeed, this won't matter much (even for a chemist), but this is not a problem just for intergalactic engineers (and please do remember the fact that it is the International Union of Pure and Applied Chemistry that is updating these not a bunch of astronomers working at/for NASA).

2009 called, its wants its article back (-1)

Anonymous Coward | more than 3 years ago | (#34559140)

3 year old article?

Holy crap (1)

LordVader717 (888547) | more than 3 years ago | (#34559170)

Next they'll be telling us their weight depends on their energy too.

Proper summary: (1)

Chris Mattern (191822) | more than 3 years ago | (#34559194)

Elements have isotopes, different isotopes have different atomic weights, the proportion of isotopes present differs from sample to sample, the standard periodic table reports an average atomic weight that may or may not be appropriate to the sample you're considering at the moment. Way to report the scientific news of 70 years ago.

Location of nuke material (1)

frith01 (1118539) | more than 3 years ago | (#34559342)

Hasnt this always been known that even different mines from the same countries produce isotope "fingerprints" that let the 3 letter agencies identify where nuke material come from? This is simply making it more obvious to those who use the reference for the range of values found so far ?

The consequences for Carbon Dating... (1, Insightful)

Rhodri Mawr (862554) | more than 3 years ago | (#34559348)

...are that it's proved to be a completely inappropriate way of measuring the age of a sample, particularly for older samples.

In fact for any sample over 2000 years old the errors are absolute.

So in fact, this is big, big news.

Re:The consequences for Carbon Dating... (0)

Anonymous Coward | more than 3 years ago | (#34559506)

Let me guess, you are trying to use this to "prove" your creationist myth.

Re:The consequences for Carbon Dating... (1)

Rhodri Mawr (862554) | more than 3 years ago | (#34559588)

Keep guessing, coward.

Re:The consequences for Carbon Dating... (0)

Anonymous Coward | more than 3 years ago | (#34559956)

Only if you don't understand how science works. If you think distribution of isotope is entirely unpredictable, (or perhaps being tampered with by a mischevious God?), you might conclude that carbon dating is unreliable - but probably the only people who would do that are grasping at straws for any possible excuse to reject science that contradicts their literal interpretation of religious dogma.

Re:The consequences for Carbon Dating... (1)

Beezlebub33 (1220368) | more than 3 years ago | (#34560166)

Um...no. Why would you think that? Do you have any citations for this?

We know that the isotope concentration of C14 changes in the atmosphere, and we think we know why. That's why the dates are calibrated against other ways of estimation (dendrochronology, ice cores, varves, etc). We also know that C14 is not uniformly distributed because there are carbon sinks (oceans, rivers from ice melt, etc.), so that is taken into account as well. The referenced paper has no bearing on this at all, and radiocarbon dating is good to at least 20,000 years ago. So, what are you talking about?

atomic weight is not very useful (0)

Anonymous Coward | more than 3 years ago | (#34559494)

They should be measuring lean muscle mass.

Not that surprising (2)

raovq (999171) | more than 3 years ago | (#34559536)

This isn't a big shock. In nature, there is a process called isotope fractionation. The idea is simple, in biological systems lighter isotopes react faster. Also with something like the evaporation of water, the heavy water will naturally be discriminated against. This means that in plants, carbon 13 and especially 14 do not react as quickly as carbon 12. The plants as a result contain less carbon 13 and 14 than you would otherwise expect. We usually measure this depletion against a worldwide limestone standard, when values carbon 13 can be up to 30% less for oils and fuels which have been processed by plants and microbes. We can actually use the depletion value to determine if an oil is 'ready' to be extracted and its quality or find what plant (or type of plant) a sample may have come from. While this is a very well documented and understood phenomenon, it has safely been ignored up until now. In test tubes the isotopes react more or less the same and most chemists don't give it a second thought. Any real work that needs very precise and accurate masses can utilize equipment like high res mass spec, which can tell you the amount of each isotope present. This paper proposes using an interval to cover this fractionation that can occur, making the point that you cannot assume the ratio of carbon 12 to carbon 13 (or any other element) is constant throughout the universe, which changes the average molecular mass.

In other news (1)

chiark (36404) | more than 3 years ago | (#34559694)

The pope has been found to be catholic, birds fly, fish swim and bears defecate in woods.

This sounded like it might be a fundamental change in something big, but it isn't. As many have already said, anyone with a passing knowledge of chemistry - even misremembered over 19 years like mine - is aware of the underlying reasons and the implications!

It's presented as sensational but it's really not news in any way, shape or form.

Re:In other news (1)

khr (708262) | more than 3 years ago | (#34560168)

The pope has been found to be catholic, birds fly, fish swim and bears defecate in woods.

quote>

While I don't know about the pope, but there's birds that swim, fish that fly, bears that defecate outside the woods and other things that defecate in the woods...

Mass fractionation is everywhere! (0)

Anonymous Coward | more than 3 years ago | (#34559762)

Lots of chemical reactions can significantly fractionate isotopes, although the effect is typically small (of the order of a few tens of parts per thousand at most) and often negligible for normal chemistry. The effects are larger in light elements because the relative differences in mass between isotopes are bigger e.g. deuterium is twice as heavy as normal hydrogen. For heavier elements like iron, fractionation effects still exist, but are orders of magnitude smaller.

One example is evaporation of water: 16O evaporates more easily than 18O. Thus the "average" atomic weight of oxygen in seawater is higher than that of rainwater. The magnitude of the fractionation effects depends on the isotopes, but also on temperature and reaction kinetics, so there may be a lot of useful information in these small differences.

People (especially geochemists) have been doing work using these effects for decades, making use of the differences in isotopic ratios through space and time to investigate earth and biological processes. Try Googling stable isotope geochemistry..

However, having an "average" value on periodic tables is still useful - for most bulk-compositional calculations such an approximation is entirely appropriate.

Cheers

J

So how is this news? (0)

Anonymous Coward | more than 3 years ago | (#34559902)

I learned back around 1970 that it was already standard practice to identify the source of metal samples (e.g. in captured weapons) by measuring the ratios of the stable isotopes - there was some index somewhere of which eastern European mines yielded which isotope ratios. Archaeologists have been tracking the movement of metals and jewels by looking at isotope ratios to determine where the sample came from. Someone even found that the ratios of stable iron isotopes differ between young adult men and women - to name only a very few uses of isotope ratios.

VYOU FAIL iT (-1)

Anonymous Coward | more than 3 years ago | (#34559952)

lu3k I'll find arithmetic,

Weight vs mass (1)

TeknoHog (164938) | more than 3 years ago | (#34560122)

I thought it was obvious: the mass of a given atom is constant, but measure its weight in different locations (equator, north pole, the moon) and you get different results. Of course, I'm just a simple physicist.

Reality? (1)

khr (708262) | more than 3 years ago | (#34560148)

"People are probably comfortable with having a single value for the atomic weight, but that is not the reality for our natural world"

They didn't consult Karl Rove [wikipedia.org] for this, did they?

Somehow this make sense (1)

rickb928 (945187) | more than 3 years ago | (#34560368)

Trying to discuss theoretical physics with a skilled theoretical physicist is like playing card with someone who plays by changing the rules when they are losing. So long as you're not betting much on it, what the heck. And when they go all in, well, we know they must not be playing with their own money.

Time for a new periodic table! (1)

Chemisor (97276) | more than 3 years ago | (#34560768)

You heathens just keep screwing things up worse and worse. Everybody knows that there is only one true periodic table: Fire Earth Air Water [jumbojoke.com]

Nothing new here (0)

Anonymous Coward | more than 3 years ago | (#34561392)

Typical of the hyping of science news. I remember reading this about lead a long time ago. In fact the isotope ratios of lead are used to characterize bullets for forensic analysis. At work we had to account for the actual isotope ratio of Lithium 6 vs Lithium 7 in calculating the purity of a lithium hydroxide sample. We believe the lithium was waste from lithium that had been isotopically enriched for nuclear weapons.

Not News (1)

bky1701 (979071) | more than 3 years ago | (#34562264)

Many periodic tables even state it is the average mass of all samples. Any element with common isotopes is going to vary depending on where it is found; the same goes for carbon, which is how carbon dating works. Even largely stable elements that do not have a gas form could vary in extreme conditions.
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