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Atomic Weight Not So Constant

Posted by kdawson on from the thulium-and-thalium dept.

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."

97 of 147 comments (clear)

  1. You know the cliché by Anonymous Coward · · Score: 2, Funny

    American atoms are fat.

    1. Re:You know the cliché by NoSleepDemon · · Score: 1

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

    2. Re:You know the cliché by Yvanhoe · · Score: 1

      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....

      --
      The Wise adapts himself to the world. The Fool adapts the world to himself. Therefore, all progress depends on the Fool.
    3. Re:You know the cliché by Jeff+DeMaagd · · Score: 1

      One woman on Science Friday interview said something that throws it off is that when the US collects its numbers, it weighs the people sampled. In other countries, often they just ask, and people tend to give a number that's probably off by several percent. This might have changed in the last year or so, I don't know.

    4. Re:You know the cliché by c6gunner · · Score: 1

      Yeah, I agree that comparing these measurements in general is a bit ridiculous. It's much more interesting (and useful) to look at how various societal factors correlate to the change in BMI over time.

      On the other hand, I think these stats can be quite valuable for dispelling myths. For instance, I don't think anyone pictures Greeks as particularly obese (quite the opposite, actually), while Americans have a reputation for being a nation of gluttons. Looking at some of these figures has changed some of my own personal misconceptions, so there's definitely some value in comparing the statistics; it only becomes silly when you use them to engage in nationalistic pissing contests.

      Also, to be fair, the "sarcastic trollish comment" you were responding to was hardly the only one in the series; the entire thread is a collection of trollish (though amusing) comments, so don't put all the blame on that one guy :)

    5. Re:You know the cliché by camperslo · · Score: 1

      Yeah, I agree that comparing these measurements in general is a bit ridiculous. It's much more interesting (and useful) to look at how various societal factors correlate to the change in BMI over time.

      Yes, there is much to be learned looking at the increases in obesity over time. The U.S. corn subsidies, lower-protein corn engineered for the production of high fructose corn syrup, and the widespread use of corn syrup directly and indirectly in foods has been shown to have had a major impact. (An example of a harmful indirect use is for feeding cattle. They're higher fat and harbor more-harmful strains of E-coli due to the higher acidity the diet causes)
      A long list of related links is available from the page for the documentary King Corn which was presented within the PBS Independent Lens series.

      http://www.pbs.org/independentlens/kingcorn/more.html

      Here is simple graphic for seeing where one is as far as Body Mass Index.
      (a separate table adjusted with slightly less massive norms for Asians is also available)

      http://en.wikipedia.org/wiki/File:Body_mass_index_chart.svg

      The U.N. and W.H.O. have extensive obesity data available which shows variation over time, by region, by gender etc. (sorry I don't have time to refind the links to the excellent sources I've seen there previously)
      It's not a contest between countries. Finding obesity in other nations certainly doesn't make it any less serious at home.

    6. Re:You know the cliché by c6gunner · · Score: 1

      The U.S. corn subsidies, lower-protein corn engineered for the production of high fructose corn syrup, and the widespread use of corn syrup directly and indirectly in foods has been shown to have had a major impact.

      Lets just say I find the data unconvincing. It's been repeatedly shown that, as far as weight-loss/gain is concerned, the only thing that matters is calories in and calories out. You can eat a balanced diet of 4,000 calories a day and you'll gain weight, or drink 2,000 calories of pure fructose corn syrup a day and you'll lose weight. Professor Haub provided the most recent example of that principle, when he pulled his little Twinkie Diet stunt. People who tell you otherwise are generally trying to sell you their own super-seeekrit 100% GUARANTEED to work Miracle-Diet (tm).

      The only way in which the use of high-fruictose corn syrup could lead to weight gain in a population is if it's use directly lead to the increase in caloric content of the average meal. However, you'd get the same result by adding any other type of sugars, so it's irrational to blame the product if the real issue is the usage.

      Here is simple graphic for seeing where one is as far as Body Mass Index.
      (a separate table adjusted with slightly less massive norms for Asians is also available)

      Yeah, I've always found those tables to be completely useless. When I was 17, I was 5'10" and 180 lbs. I could pump out 100+ pushups, 40+ chinups, climb the gym ropes faster than most people could walk the same distance, and when I joined the military a year later I kicked everyones ass on the obstacle course. Yet, according to that chart, I was "overweight", and halfway to "obese". Looking at the same figures, I could safely say that at least three quarters of the people I worked with in the infantry would have likewise been considered "overweight". That's one of the reasons I've never put much stock in BMI measurements, although they can be useful when you're studying populations as opposed to individuals (assuming you're not dealing with unusual populations / samples, eg. military, firemen, bodybuilders, etc). I'd like to see body-fat percentage measurements replace BMI as a standard measurement of obesity, though - they tend to give a much better indication of fitness / health levels.

    7. Re:You know the cliché by tchdab1 · · Score: 1

      It's global warming, it causes everything to rise.

    8. Re:You know the cliché by bolthole · · Score: 1

      I was 5'10" and 180 lbs. I could pump out 100+ pushups, 40+ chinups,

      that makes you not fit the "profile" to begin with. Generic BMI is only supposed to be used for people with "average" physique. "average" people cant do half of that.
      Obviously, you have/had way more muscle than the average.

      I'd like to see body-fat percentage measurements replace BMI as a standard measurement of obesity

      well of course that would be better... but most people dont have an accurate "body fat measurement device".
      They DO, however, have a scale and a tape measure.

      (it's odd, though, that even hospitals dont normally measure body fat%: just "height and weight")

      Your post made me look around to see if they now have reasonably priced body fat measurement devices...
      And they DO! $40 for some at target, etc. I am intrigued.

    9. Re:You know the cliché by Xaositecte · · Score: 1

      Then our profile of an "average" person is someone who has never seen the inside of a gym. I only work around twice a week these days, and can still crank out 100+ push-ups (in sets of ~40, not all at once) if I have to.

      Much like GP, my BMI is just edging into the "overweight" category at 6'2" and 200 lbs.

    10. Re:You know the cliché by Belial6 · · Score: 1

      I get hydrostatically weighed every few months. At 5'11, my lean body mass of 180lbs means that even if I reduced my body fat to 0%, I would still be overweight. I don't work out at all.

    11. Re:You know the cliché by Belial6 · · Score: 1

      The fat measurement scales you buy at Target do not work. I get hydrostatically weight for body fat, and the scales that claim to measure body fat are little better than guesses. I wish they did work. The OP has "greater than average muscle", I have "greater than average muscle", the next guy has "greater than average muscle". The BMI is a total joke. If the distribution of weight to height is a valley, it can be wrong for just about everybody. If it is straight, it is wrong for the majority. If it is a peak, it is wrong enough to be worthless.

      It IS odd that hospitals don't use body fat%. It is even more odd that gyms don't use body fat %. The equipment to hydrostatically weigh people just isn't that complicated, nor does it take up that much space. I have to drive over 100 miles to get to the nearest location that does hydrostatic weighing, and that is a mobile unit that pretty well covers all of Northern California. Of course, if people were using body fat %, the people being told that they were bad because they were fat would drastically shift.

    12. Re:You know the cliché by Belial6 · · Score: 1

      I call shenanigans. I have offered many a bet that I can put on weight eating a 2500 calorie a day diet, and lose weight at a 4000 calorie a day diet. This with absolutely no change in exercise.

      The calories in, calories out myth has be thoroughly debunked. It is a good premise for life forms that do not have anuses, and that have 100% matter/energy conversion digestive systems, but that does describe humans. Can you really say that you have never met someone who worked out a lot, and watched what they ate yet still was fat, and never met someone who ate all of the time and never got exercise, yet remained thin?

      I agree that the BMI is worse than useless. It is dangerous. My lean body mass (hydrostatically weighted) is 2 pounds more than the cutoff for 'normal' weight, putting me as overweight. To stop being overweight, getting down to 0% body fat wouldn't be enough. I would literally have to amputate. Taking off a leg would do it. I would have to be careful though because if I made a wrong decision and amputated both legs, I would suddenly be shorter and would be 'overweight' again.

      While your logic of 'what you eat' doesn't matter is flawed, you are correct that corn syrup is not likely the poison many claim. Well, no more the poison than any other sugar. The problem is that an almost entirely sugar diet is considered 'healthy' and 'balanced'. This means that when people cut out the corn syrup, they invariably move to other sugars like pasta or bread, and feel good about how they are now eating 'healthy'.

    13. Re:You know the cliché by camperslo · · Score: 2

      The calories matter, but very little fructose can be used by the body directly compared to glucose. It gets converted to fat. If you're pretty active, you can burn that fat. But for things like providing the energy your brain needs, it isn't metabolized well. You can actually feel short on energy at the same time you're converting fructose to fat. The liver has to work harder to process it too. Most of the time what people perceive as energy from a soda is actually the caffeine.
      And with fructose, your brain is less apt to tell you you're full, so gulping down large amounts of fructose is way too easy. It's junk calories that can contribute to fat without doing anything useful.
      It's a waste of money. If you tried to live on 2000 calories of fructose a day you may not get fat but it wouldn't take long to be sickly.

      Obesity in the U.S. has become much more of a problem since we started subsidizing corn in the Reagan era. The very high yield variety that is profitable (with subsidy) is very low protein and not suitable for eating. It does get fed to cows since it fattens them quickly, resulting in a more sickly and fat-loaded beef supply. It's a very unhealty diet for cows which would kill them if they weren't pumped full of antibiotics. It degrades our food supply in more ways than are obvious at a glance.

      http://www.huffingtonpost.com/dr-mercola/sugar-may-be-bad-but-this_b_463655.html

    14. Re:You know the cliché by c6gunner · · Score: 1

      I call shenanigans. I have offered many a bet that I can put on weight eating a 2500 calorie a day diet, and lose weight at a 4000 calorie a day diet. This with absolutely no change in exercise.

      I would gladly take your bet, if I could monitor you 24/7 for the duration of the experiment. If I lost - which is unlikely - we'd have learned something useful about human metabolism. If I won ... well, I don't mind taking your money :)

      The calories in, calories out myth has be thoroughly debunked.

      Riiiiight. Feel free to follow the link I posted. The "calories in calories out myth" is pretty much the accepted standard in the scientific community. It's only been "debunked" by protein-powder-pushing muscle-heads with a 6th grade education.

      (ok, I'm exaggerating a bit, but really, what did you expect when you made that claim?)

      Can you really say that you have never met someone who worked out a lot, and watched what they ate yet still was fat, and never met someone who ate all of the time and never got exercise, yet remained thin?

      I've met lots of people who THINK they're watching what they're eating, but when you sit down with them and run the numbers it turns out they're underestimating their daily intake by 1,000+ calories. I've also met people who have a high metabolism and are quite thin despite eating lots - that's all part of the calories-in-calories-out thing. If you have such a fast metabolism that you burn twice as many calories as an average person even when you're resting, obviously you're going to be thinner.

      Most importantly, though, anecdote != data. It doesn't matter how many purple alien lizards you think you've seen - it's not going to convince me that we're being invaded.

    15. Re:You know the cliché by vegiVamp · · Score: 1

      You mean you actually *have* an economy, these days ?

      --
      What a depressingly stupid machine.
  2. Actual Link to Document by Fluffeh · · Score: 5, Informative

    Link to actual article is:
    link

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    1. Re:Actual Link to Document by chichilalescu · · Score: 5, Informative

      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.

      --
      new sig
    2. Re:Actual Link to Document by JustOK · · Score: 1

      the value of the findings vary depending on the observer.

      --
      rewriting history since 2109
    3. Re:Actual Link to Document by Interoperable · · Score: 5, Informative

      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.

      --
      So if this is the future...where's my jet pack?
    4. Re:Actual Link to Document by Magic5Ball · · Score: 1

      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.

      --
      There are 1.1... kinds of people.
    5. Re:Actual Link to Document by NeverVotedBush · · Score: 2

      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.

    6. Re:Actual Link to Document by Rich0 · · Score: 1

      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...

    7. Re:Actual Link to Document by ari_j · · Score: 1

      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.

    8. Re:Actual Link to Document by Anonymous Coward · · Score: 2, Informative

      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).

    9. Re:Actual Link to Document by JustOK · · Score: 1

      mebbe for you they don't

      --
      rewriting history since 2109
    10. Re:Actual Link to Document by jc42 · · Score: 1

      Yeah; my first reaction was "WTF? Archaeologists have been using variations in isotope ratios for decades as a way of learning about the diet of the people and other critters who left remains." This works (sort of) because different plant species have different isotope ratios for many of their constituent elements. Isotope ratios are also used to do things like locate the source of plant, mineral and metallic objects. Anyone who knows about this understands that the published "atomic weight" numbers are rough approximations, and will vary depending on the source of the samples.

      How is this a news story at all? Maybe the news is that there exists someone with a technical background who doesn't understand that published atomic weights are only approximations.

      --
      Those who do study history are doomed to stand helplessly by while everyone else repeats it.
    11. Re:Actual Link to Document by Coren22 · · Score: 1

      I was a little surprised by the summary, as I don't recall ever seeing atomic weight on the periodic table. The only number I recall seeing as a constant was the only constant that can be used; the number of protons.

      http://en.wikipedia.org/wiki/Periodic_table

      --
      APK likes to ask for responses to the same things over and over. Maybe he just likes the responses?
    12. Re:Actual Link to Document by osu-neko · · Score: 2

      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.

      Has it ever been explained why kdawson posts usually have titles that are flat-out contradicted by the article in question? Perhaps another study is in order...

      --
      "Convictions are more dangerous enemies of truth than lies."
    13. Re:Actual Link to Document by c++0xFF · · Score: 1

      I've always been bothered by the fact that no standard deviation is ever given. Of course, there's not much room on there for that info on a periodic table, but I don't even see it when the full properties are listed.

      TFA presents the value as a range ([1.007 84; 1.008 11] for Hydrogen). Why not say 1.00798 +/- 0.014%. IANAC (chemist), but that seems to give the same information, but in a way that's more natural to the way people will use the value. Unless I know what the correct average weight is where the sample was taken, I should probably be using the worldwide average anyway (but then include the error bars).

    14. Re:Actual Link to Document by micheas · · Score: 1

      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.

      I can see some changes in that it seems like one might be able to find the average atomic weight of some Al and make an educated guess at where it was mined, It also means that if you are looking for a particular isotope, it might be worthwhile to start with ore from one location rather than another.

      While I agree that they seem to be overstating the significance, this may have real world effects, so it is at least a small advance.

      --
      Work bio at MMWD
    15. Re:Actual Link to Document by vegiVamp · · Score: 1

      How does that work ? Does that mean Pb can vary between 207.20 and 207.29... ? How about when the weight of an element could vary between, say, 200.45 and 200.47 ?

      --
      What a depressingly stupid machine.
    16. Re:Actual Link to Document by Thud457 · · Score: 1

      obviously someone who's never gotten his hands dirty in a physics lab

      --

      the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff

    17. Re:Actual Link to Document by HeadlessNotAHorseman · · Score: 1

      the value of the findings vary depending on the observer.

      That's why it's so hard to get string theory off the ground - because at a quantum level you change the value of the findings by observing them!

      --
      I like my coffee the way I like my women - roasted and ground up into little tiny pieces.
  3. I don't get it by FTWinston · · Score: 3, Insightful

    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.

    1. Re:I don't get it by Sockatume · · Score: 5, Informative

      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.

      --
      No kidding!!! What do you say at this point?
    2. Re:I don't get it by SimonTheSoundMan · · Score: 2

      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.

    3. Re:I don't get it by Marcika · · Score: 4, Informative

      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".

    4. Re:I don't get it by Lloyd_Bryant · · Score: 2

      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 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.

      --
      Don't tell me to get a life. I had one once. It sucked.
    5. Re:I don't get it by jo_ham · · Score: 1

      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.

    6. Re:I don't get it by vlm · · Score: 1

      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.

      --
      "Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
    7. Re:I don't get it by PrinceAshitaka · · Score: 1

      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.

      --
      quis custodiet ipsos custodes
    8. Re:I don't get it by FTWinston · · Score: 1

      Yeah, that was my interpretation also.

    9. Re:I don't get it by LWATCDR · · Score: 1

      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.

      --
      See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
    10. Re:I don't get it by pclminion · · Score: 1

      it is *not* a "weight" in any sense of the word.

      Yes it is. It is a weight in the sense meant by the term "atomic weight."

      But if you really want change for change's sake (it's not like this leads to confusion among chemists), let's call it atomic mojo. How about that?

    11. Re:I don't get it by shaitand · · Score: 2

      The atomic weight has always been a weighted average that isn't new. What is new is that they are no longer going to print that average as the singular atomic weight. Now they are going to print a range because the abundance of a given isotope varies based on where a sample is gathered.

    12. Re:I don't get it by Jookey · · Score: 1

      I can't believe I got modded down for sarcasm. Whats happened to Slashdot.

  4. Isotopes by MichaelSmith · · Score: 4, Insightful

    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.

    --
    http://michaelsmith.id.au
    1. Re:Isotopes by The_mad_linguist · · Score: 1

      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.

    2. Re:Isotopes by aliquis · · Score: 2

      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?

    3. Re:Isotopes by smellsofbikes · · Score: 1

      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 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.

      --
      Nostalgia's not what it used to be.
  5. Atomic Weights were never constant by bhaak1 · · Score: 5, Insightful

    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" as even Wikipedia knows?

    Somebody seemed to have failed his physics or chemistry classes.

    --
    UnNetHack: NetHack Improved!
    1. Re:Atomic Weights were never constant by ciderbrew · · Score: 2

      Is the level of bitch a constant?

    2. Re:Atomic Weights were never constant by TeethWhitener · · Score: 1

      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.

    3. Re:Atomic Weights were never constant by bhaak1 · · Score: 1

      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.

      I didn't really mean the scientists in question. But as is usual nowadays, ./ headlines and summaries are often quite incorrect.

      Even though the stories are seen by several people before the hit the front page.

      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.

      :-)

      --
      UnNetHack: NetHack Improved!
  6. Meh by Zironic · · Score: 3, Insightful

    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!!!"

    1. Re:Meh by jo_ham · · Score: 1

      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.

    2. Re:Meh by vlm · · Score: 1

      Everything stable that isn't one of the monoisotopic elements

      http://en.wikipedia.org/wiki/Monoisotopic_element

      --
      "Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
    3. Re:Meh by JoeRobe · · Score: 1

      I agree. People who work with the atomic weights are aware that they are averages of multiple isotopes. Mass spec folks never use the average values. The 35.453 of Chlorine may change from region to region on Earth by a fraction of a percent, but the problem is that if you're doing something that needs the rough average value (e.g. calculating the mass of HCl in a lecture bottle), you now can't just look at the periodic table and get the atomic weight. You have to look up the local ratio and then calculate the average based upon that.

      --
      The best way to predict the future is to invent it.
  7. Masses not changing; only ratio of isotopes. by Anonymous Coward · · Score: 4, Informative

    The scientific paper can be found here.

    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.

  8. Not surprising by srussia · · Score: 1

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

    --
    Set your phasers on "funky"!
  9. Acronym of union by skywatcher2501 · · Score: 1

    Wait let me guess.. IUPACHCIAW, right??

  10. Why not look in Wikipedia first? by astrobotanic · · Score: 1

    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

  11. Re:Natural constants? by nschubach · · Score: 1

    *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.)

    --
    Every time I start to have faith in humanity, I ruin it by driving to work between 7 and 8 am.
  12. Comment removed by account_deleted · · Score: 5, Informative

    Comment removed based on user account deletion

  13. Re:Natural constants? by mattr · · Score: 1

    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..

  14. Holy crap by LordVader717 · · Score: 1

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

  15. Re:Natural constants? by vlm · · Score: 5, Insightful

    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.

    --
    "Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
  16. Re:Natural constants? by digitig · · Score: 1

    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).

    --
    Quidnam Latine loqui modo coepi?
  17. Proper summary: by Chris+Mattern · · Score: 1

    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.

  18. Wrong assumption by Arrepiadd · · Score: 2

    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.

    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).

  19. Location of nuke material by frith01 · · Score: 1

    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 ?

  20. The consequences for Carbon Dating... by Rhodri+Mawr · · Score: 1, Insightful

    ...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.

    1. Re:The consequences for Carbon Dating... by Rhodri+Mawr · · Score: 1

      Keep guessing, coward.

    2. Re:The consequences for Carbon Dating... by Beezlebub33 · · Score: 1

      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?

      --
      The more people I meet, the better I like my dog.
    3. Re:The consequences for Carbon Dating... by smellsofbikes · · Score: 3, Informative

      ...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.

      I'd be curious to see where it's been "proved" to be an inappropriate way of age measuring, since carbon-14 dating closely correlates with tree ring data out to 26,000 years back, using the INTCAL04 data group, which is internationally recognized as valid, and likewise it correlates well with deep ocean sediments, coral, cave rock formations, and other sources, all of which give similar age data to radiocarbon dating, which is currently using the INTCAL09 data for correction, that is internationally recognized as valid out to 50,000 years. So, if there's a problem with radiocarbon dating, the same problem is also affecting how fast sediments accumulate, coral grow, and stalactites form, and I've never heard of anyone suggesting anything that can affect all those, at the same time, and alter them all in a proportional manner. If you've any suggestions for something that could do that, I'd love to hear about it.

      --
      Nostalgia's not what it used to be.
  21. Comment removed by account_deleted · · Score: 1

    Comment removed based on user account deletion

  22. Not that surprising by raovq · · Score: 2

    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.

  23. In other news by chiark · · Score: 1
    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.

    1. Re:In other news by khr · · Score: 1

      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...

    2. Re:In other news by not-my-real-name · · Score: 1

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

      I'm an ostrich you insensitive clod.

      --
      un-ALTERED reproduction and dissimination of this IMPORTANT information is ENCOURAGED
  24. Weight vs mass by TeknoHog · · Score: 1

    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.

    --
    Escher was the first MC and Giger invented the HR department.
  25. Reality? by khr · · Score: 1

    "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 for this, did they?

  26. Re:Natural constants? by Shining+Celebi · · Score: 1

    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.

  27. Somehow this make sense by rickb928 · · Score: 1

    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.

    --
    deleting the extra space after periods so i can stay relevant, yeah.
  28. Re:Natural constants? by NeverVotedBush · · Score: 1

    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.

  29. Time for a new periodic table! by Chemisor · · Score: 1

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

  30. Re:Natural constants? by andrewagill · · Score: 2

    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...

  31. This has been known since 1972 by DrNoNo · · Score: 1

    The Oklo natural nuclear reactors http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor were discovered on the basis of isotope ratio deficiency

  32. Re:Natural constants? by flintmecha · · Score: 1

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

    Pi would like a word with you.

  33. Re:Natural constants? by Tyler+Durden · · Score: 1

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

    --
    Happy people make bad consumers.
  34. Not News by bky1701 · · Score: 1

    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.

    --
    Great Intellect...
  35. WORST TFA EVVAR! by ediron2 · · Score: 1

    I feel dumber for having clicked that link:

    Newfoundland comedian wha?

    Bane of high school students everywhere huh?

    Stupid jokey crap that never ends?!

    Shit, if I want god-knows-how-many-paragraphs of lead-in followed by a bunch of handwavy bullshit seemingly intended for people that enjoy feeling smart without having to think or understand things, I'd get a subscription to People magazine.

    While the underlying news is definitely for nerds, THIS was not the link we're looking for.

  36. Score one for general semantics by mikeymoto · · Score: 1

    Just because it's measured one way in one place or time...

  37. Re:Natural constants? by arkane1234 · · Score: 1

    You mean just like atomic weight is a constant?

    --
    -- This space for lease, low setup fee, inquire within!
  38. Re:Natural constants? by Wonko+the+Sane · · Score: 1

    This article isn't about atomic weights changing. It's about estimates of isotopic ratios found in nature changing.

  39. Re:Fructose Hypothesis by glodime · · Score: 1

    The partially explained hypothesis in that article is mildly interesting, however, as with much of Huffington Post's reporting on health issues, there is no indication of data to support the theory. It is just a single Doctor offering personal observations and fitting it to a theory.

    Using Occum's razor perhaps the most likely answer is that corn subsidies helped make the average price of calories cheaper at a time when average incomes were increasing. Companies also are motivated by profits to sell foods that are less filling per dollar. This resulted in increased caloric intake by most people and was accompanied by shift to a more sedentary lifestyle. So caloric intake increased and metabolic caloric expenditure decreased on average. The burden of proof lies with the claim that fructose of equal caloric value will lead to increase in weight compared to other calories. So far the evidence is lacking.

    I've seen evidence that the increase in corn in the diets of livestock has changed the composition of fat ingested by people in the USA. This composition change may contribute to cardiovascular and other diseases but not to weight gain.

    As Mark Haub recently demonstrated, the evidence for calorie control as the route toward weight loss is quite convincing. However, overall health is much more complicated than, though certainly influenced by, maintaining ones weight.