Frowning takes 68 muscles.
Smiling takes 6.
Pulling this trigger takes 2.
I'm lazy.
Posted on 12/15/2010 5:23:20 PM PST by smokingfrog
For the first time in history, a change will be made to the atomic weights of some elements listed on the Periodic table of the chemical elements posted on walls of chemistry classrooms and on the inside covers of chemistry textbooks worldwide.
The new table, outlined in a report released this month, will express atomic weights of 10 elements - hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium - in a new manner that will reflect more accurately how these elements are found in nature.
"For more than a century and a half, many were taught to use standard atomic weights — a single value — found on the inside cover of chemistry textbooks and on the periodic table of the elements. As technology improved, we have discovered that the numbers on our chart are not as static as we have previously believed," says Dr. Michael Wieser, an associate professor at the University of Calgary, who serves as secretary of the International Union of Pure and Applied Chemistry's (IUPAC) Commission on Isotopic Abundances and Atomic Weights. This organization oversees the evaluation and dissemination of atomic-weight values.
Modern analytical techniques can measure the atomic weight of many elements precisely, and these small variations in an element's atomic weight are important in research and industry. For example, precise measurements of the abundances of isotopes of carbon can be used to determine purity and source of food, such as vanilla and honey. Isotopic measurements of nitrogen, chlorine and other elements are used for tracing pollutants in streams and groundwater. In sports doping investigations, performance-enhancing testosterone can be identified in the human body because the atomic weight of carbon in natural human testosterone is higher than that in pharmaceutical testosterone.
(Excerpt) Read more at eurekalert.org ...
How much is earmarked for this change?
I had to take chemistry in college, but, it turned out ok because I could check out all the stuff I needed to make a very high quality still and the nerdy chem lab assistant hadn’t a clue.
Well, for starters human testosterone has carbon-14 in it, while that made from petroleum has had millions of years during which it has all decayed. (This is how “carbon dating” works.) Furthermore, there is a natural isotopic abundance of C-13, about 1% of naturally-occurring carbon is this. But the ratios aren’t exactly the same everywhere, and it’s entirely possible that C-13 is more abundant in human bodies than it is in oil. It wouldn’t have to be much more to be detectably more.
But when you weigh out carbon in, say, sodium carbonate, it’s a mixture, and so you should calculate it based on the relative abundance of the two isotopes in your carbonate sample. Except that this ratio varies by source, which is the entire point of the whole exercise. What the exact masses of the pure isotopes is (1) is already known and (2) isn’t what is being changed here.
Guess somebody has found a way to sell a few extra periodical table charts during 2011.
“Isotopic MIXTURE” M-I-X-T-U-R-E ... meaning... more than one pure isotope.
It’s a ratio.
Actually you should be doing the opposite. The chemical reactions permit you to calculate the relative isotope mixture in the sodium carbonate.
Ok, and why should the periodic tables care about isotope mixtures? They already list the most stable isotope and when I’m dealing with a mixture, I can use this number against experimental data to derive the actual mixture ratio from the ratio of the expected vs actual weights.
By fudging the numbers, I have to look up the common isotope masses every time. Worthless.
A myth propagated by muslims who are embarassed at the fact that islam has given nothing but death and destruction to the world since its founding. The concept of 'zero' was imported from India by muslims who'd conquored them, then promptly done nothing whatsoever with the idea.
Yes, and this is why the Periodic table is so useful because it teaches you the basics of atomic theory. Each element has common characteristics with the element below it in the table due to the arrangement of protons and electrons.
Atomic mass is a convention. You could use kilograms just as well, but it’s far easier and more convenient to use the atomic mass of Carbon (which is pretty close to 12x the mass of a proton) and set the scale up so that everything is a ratio of Carbon 12.
Fudging the numbers makes it impossible to understand what’s an element and what is an isotope. You’ve changed the definition of the ‘atomic mass’, to something that has no bearing to reality. It no longer corresponds with the number of protons, neutrons and electrons.
Carbon is already lighter than oxygen. Did you mean hydrogen?
Clue: It is 'atomic weight, not isotopic weight. The periodic table lists the atomic weight for the most common ratios of isotopes in nature. You should NOT be using the the weight of the most stable isotope. If you are getting the weight from the periodic table you are most probably already using the weight of the mixed isotopes. If you look at the periodic table for oxygen, you will see that and also see that it has references that the stated uncertainty is inclusive of the variation of the isotopes found in nature. So if you are properly accounting for the error in the atomic weight then your answer would have a range of values. Basically this is nothing really new. Now the uncertainty is just stated as a range.
Because most elements occur in mixtures of isotopes.
They already list the most stable isotope
?The most stable one? Either an isotope is stable, or it isn't. Cl-35 and Cl-37 are both stable. Which one is more stable? Maybe you mean abundant. But a periodic table doesn't tell you the abundance (although you can work it out when there are only two, as in the case of Cl). It just says the atomic weight is 35.453, as a result of it being a mixture of 35 and 37. When there are three or more isotopes, you can't deduce the relative amounts from the average weight.
and when I’m dealing with a mixture, I can use this number against experimental data to derive the actual mixture ratio from the ratio of the expected vs actual weights.
Only when there are two isotopes. And only when you're dealing with a lot of significant figures.
By fudging the numbers, I have to look up the common isotope masses every time. Worthless.
You're confusing a table of isotopes with a periodic table. The isotopic weights as reported on a table of isotopes isn't changing. Only the periodic table atomic masses, averaged over abundance, are changing.
You lose. Many atomic weights are known to six decimal places. Those are the ones with only one stable isotope. Larger uncertainties are included for those with more than one stable isotope due to the varying ratios of isotopes in nature. Existing tables have references to the uncertainties. Use those uncertainties.
But that’s not the point of the periodic table. The periodic table is intended to represent how each element relates to each other in a format that is relatively simple to understand.
“The most stable one? Either an isotope is stable, or it isn’t”.
Radioactive elements? Not all isotopes are stable and not always is the most abundant isotope stable.
“It just says the atomic weight is 35.453, as a result of it being a mixture of 35 and 37”
Wrong. You fail chemistry. The atomic mass of CL 35 is 35.453 as a result of CL 35 having 17 protons and 18 neutrons.
See what I mean? You’re already confused as to what atomic mass means because of this bullshit change. I rest my case.
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