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 ...
“I take it that you have never taken a quantitative analysis class. The 35.453 is the most important number because if you have one mole of chlorine gas, it will weigh 70.906 grams. Not 70 grams. Not 74 grams. But 70.906 grams.”
Yep sure have. Have you ever had to determine that number experimentally? It’s quite revealing.
One wonders what chemical processes can bring that about (although I for one don't wonder too awfully hard).
One, Mass and weight aren’t the same thing.
Two Relative atomic mass is the mass of the ratio of CL 35- CL 37. It has no meaning outside of the expected ratio which can very significantly.
Try 20.
Edit, 20, sorry.
Hard enough replying to two people at a time.
If so (if those were your words), you are incorrect. It is because it is a mixture of 35CL and 37CL and is a result of CL 35 having 17 protons and 18 neutrons CL 37 having 17 protons and ____ neutrons. I will let you fill in the blank”
Relative atomic mass has nothing to do with the actual properties of Chlorine. This is why it shouldn’t be on a periodic table.
Forget the periodic table for one minute and address the error you made that I was pointing out to you. If you just take one minute and google chlorine atomic weight you will see that your 35.423 is a result of a mixture of two isotopes.
In case you missed this... ping
First global warming...Now this...
Wonder if I can get a partial refund on the $65 I spent on a high-grade diamond engagement ring 53-years ago?
How did you go about doing it? Did you count the number of molecules?
Take it up with the IUPAC. I am done with you and your refusal to go google Chlorine.
The IUPAC definition 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.
I am done. Have fun.
*Sigh*
“You make some outrageous attack”
And you are being sweetness and light? Great, solid attitude here.
Relative atomic mass is not an intrinsic elemental property. It’s misleading. It assumes experimentally derived information which may or may not be the case with the actual sample.
It’s not universally applicable, and there are many applications for which it is not useful at all. This is why periodic tables should state the mass of the most common isotope which is true no matter what sample you use or how you go about doing things. Why? Because it’s related to the intrinsic characteristics of the element, the neutrons, protons and electrons. It’s not reliant upon ‘expected ratio in nature’, which isn’t always the case.
No revisionism. All they are doing is instead of stating a single number with uncertainties based on varying isotopic rations, they are specifying a range of values based on varying isotopic rations. SAME-SAME. Just in a different view.
“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.”
Which is not the definition that you are using here.
Thank you for quoting this.
an atomic mass unit or amu is one twelfth of the mass of an unbound atom of carbon-12
This does not take into account any mass defect inherent in the stability of a nuclei. It also assumes an isotopic mixture which may vary from sample to sample.
Well, they do say Carbon 12.
But a couple things here surprised me.
For one thing, I didn't know that they took the whole atom, protons, neutrons, electrons, muons, etc., and all.
And because of the packing defecit which you mention, it apparently means that a single free atom of hydrogen (not D or T) will not have a mass of exactly 1 AMU.
So today wasn't a total waste, since I learnt something--with 1 whole minute to go (in my timezone).
(Wot's with FR's clock, anyway? I guess they're using a Cesium standard based on the old weights.)
But seriously, I'm done too. It really isn't worth it.
“No revisionism. All they are doing is instead of stating a single number with uncertainties based on varying isotopic rations, they are specifying a range of values based on varying isotopic rations. SAME-SAME. Just in a different view.”
Not the same at all. Big, big difference. The old definition has the atomic mass of every element as a ratio of C-12. Now, this is no longer the case. Which is exactly the point I was trying to hammer home earlier.
The relative abundances of each element is irrelevant.
Ahmed: "Shazam! I've just discovered zero!"
Ali: "What's that?"
Ahmed: "Oh, nothing."
“And because of the packing defecit which you mention, it apparently means that a single free atom of hydrogen (not D or T) will not have a mass of exactly 1 AMU.”
Yep, you’ve got it perfectly.
That’s how it worked under the old system. Under the new system, this fact is no longer relevant. Sad, eh?
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