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The Periodic Table of Isotopes for the Educational Community

Norman E. Holden1 & Tyler B. Coplen2

1 Brookhaven National Laboratory, Upton, NY, USA
2 U.S. Geological Survey, Reston, VA, USA

June 1, 2012 - June 7, 2012
Abstract: 

The IUPAC Periodic Table of Isotopes introduces students, teachers and society to the existence and importance of stable and radioactive isotopes of the chemical elements.

This Table provides information about the basic properties of stable isotopes, their total number, their mass and abundance, which allows determination of atomic weight values of the chemical elements. This Table also provides the total number and half-lives of radioactive isotopes of each element and information on the applications of isotopes in our everyday life, as noted in the following examples. In the area of medical applications, radioactive isotopes provide for the diagnosis of disease and for its treatment. In industry, radioactive isotopes enable smoke detectors to alarm and provide an early warning of a potential fire. In geochronology, radioactive isotopes enable the dating of materials, which can provide information about migration trends of ancient peoples around the world. In the science area, ratios of stable isotopes allow the detection of illegal doping in sports activities and the detection of alteration of food and drink. Information on all 118 elements is provided. Detailed examples of the applications of specific isotopes in our everyday life are provided, except for a few of the most recently discovered elements whose half-life values are so short (much less than one second) that applications have not yet been discovered. This program is an International Year of Chemistry (IYC-2011) joint effort by members of the IUPAC Task Group Project, including J.K. Böhlke (U.S. Geological Survey, Reston, Virginia, USA), M.E. Wieser (U. Calgary, Canada), G. Singleton (U.S Department of Energy, Chicago, USA), T. Walczyk (National U. of Singapore, Singapore), S. Yoneda (National Museum of Nature and Science, Japan), P.G. Mahaffy (King’s U. College, Edmonton, Canada), L.V. Tarbox (U.S. Geological Survey, Reston, Virginia, USA), D. Tepper (U.S. Geological Survey, Reston, Virginia, USA) and the above authors.

Article PDF: 
Article PDF: 

 

IUPAC Periodic Table of Isotopes for the Educational Community

      Norman E. Holden                               Tyler B. Coplen
Brookhaven National Laboratory         U. S. Geological Survey
        Upton, New York                                Reston, Virginia

 Foreword—Here we report on progress of IUPAC project 2007-038-3-200 (http://www.iupac.org/web/ins/2007-038-3-200 ) titled “Development of an Isotopic Periodic Table for the Educational Community,” whose other members include

J. K. Böhlke, U.S. Geological Survey, Reston, Virginia
P. G. Mahaffy, King’s University College, Edmonton, Canada
G. Singleton, U.S. Department of Energy
L. V. Tarbox, U.S. Geological Survey, Reston, Virginia
D. H. Tepper, U.S. Geological Survey, Reston, Virginia
T. Walczyk, National University of Singapore
M. E. Wieser, University of Calgary, Canada
S. Yoneda, National Museum of Nature and Science, Japan

More than two person-years have gone into the development of this Periodic Table of the Isotopes (Figure 1), which we envision may reside on walls of chemistry laboratories near the Periodic Table of the Elements.

 

Introduction

John Dalton first proposed the concept of atomic weights of the elements in the first decade of the nineteenth century. These atomic weights of the chemical elements were thought of as constants of nature, similar to the speed of light. Dmitri Mendeleev arranged the atomic weights of the elements in ascending order of value and used the systematic variation of their chemical properties to produce his Periodic Table of the Elements in 1869. Measurement of atomic weight values became an important chemical activity for a century and a half. Theodore Richards received a Noble Prize for his work in this area.

 In 1913, Fredrick Soddy found a species of radium, which had an atomic weight value of 228, compared to the familiar radium gas value of 226. Soddy coined the term “isotope” (Greek for “in the same place”) to account for this second atomic weight value in the radium position of the Periodic Table. Both of these isotopes of radium are radioactive. Radioactive isotopes are energetically unstable and will decay (disintegrate) over time. The time it takes for one half of a sample of a given radioactive isotope to decay is the half-life of that isotope. In addition to having different atomic weight values, radium-226 and radium-228 also have different half-life values. Around the same time as Soddy’s work, J.J. Thomson (discoverer of the electron) identified two stable (non-radioactive) isotopes of the same element, neon. Over the next 40 years, the majority of the known chemical elements were found to have two or more stable (or long-lived radioactive isotopes that contribute significantly to the determination of the atomic weights of the elements).

Figure 1. IUPAC Periodic Table of the Isotopes (front side, version of May 25, 2012). As this Table is updated, it will be posted at the Web site of the Commission on Isotopic Abundances and Atomic Weights (www.ciaaw.org) and at the Web page for this IUPAC project (http://www.iupac.org/web/ins/2007-038-3-200).

 The atomic weight (also called the relative atomic mass), Ar(E), of element E in a substance P is expressed by the relation

Ar(E)P = ∑ [ x(iE) × Ar(iE)]

where x(iE) is the mole fraction of isotope iE (also called the isotopic abundance) and the summation is over all stable isotopes and selected radioactive isotopes (having relatively long half-lives and characteristic isotopic abundances) of the element (http://www.ciaaw.org/pubs/TSAW%202009.pdf). The standard atomic weight is determined from evaluation of published data by the Commission on Isotopic Abundances and Atomic Weights (CIAAW) of the International Union of Pure and Applied Chemistry (IUPAC) and is the best estimate of atomic weights of an element that might be found in natural terrestrial substances. The standard atomic weight of each element is dimensionless and is based upon assignment of a value of 12 exactly to the atomic weight of an unbound neutral carbon-12 atom in its nuclear and electronic ground state.

By the 2nd half of the twentieth century, the standard atomic weight of an element determined from the abundances and masses of isotopes provided a better estimate (a smaller measurement uncertainty) than the value determined by chemical measurement. Today, all new standard atomic weight values are determined from measurements of abundances and masses of their isotopes. For many chemical elements, it was discovered that their isotopic abundance values varied in different natural terrestrial samples. These variations in isotopic abundances led to variations in atomic weight values of an element. In the 1950s, the measurement uncertainty of standard atomic weight values was larger than the uncertainty due to natural isotopic variation for most elements. However, in the past five decades, improved measurements of isotopic abundances for many elements in different natural terrestrial samples yielded atomic weight values with low uncertainties that differed substantially from each other. Thus, standard atomic weight values could no longer be considered “constants of nature”, as had been commonly thought by some for the past two centuries. To bring attention to the fact that standard atomic weights of some elements are not constants of nature, the CIAAW introduced the concept of “intervals” (see below) to the standard atomic weight to account for the variation in isotopic abundances and atomic weight values in natural terrestrial substances (http://www.ciaaw.org/pubs/TSAW%202009.pdf).

 

Understanding Isotopes of Chemical Elements

The atoms of all elements are made up of a positively-charged nucleus surrounded by an equal amount of negative charge carried by surrounding electrons. Nuclei themselves are generally made up of electrically positive charged particles called protons and electrically neutral particles called neutrons (the lightest hydrogen isotope, not having any neutrons, being an exception). The number of protons in each atom (the atomic number, with symbol Z) determines the chemical element; for example, Z = 1 is hydrogen, Z = 6 is carbon, and Z = 79 is gold. The number of neutrons (symbol N) in an atom of a given element may vary. The total number of protons and neutrons (Z + N) in a specific atom is the mass number (symbol A; thus, A = Z + N). A nuclide is an atom designated by its atomic number and its mass number, written in the form of the element name (or symbol) and mass number; for example, aluminium-27 and 27Al both refer to the nuclide of the element aluminium (commonly written aluminum in the U.S.) with mass number 27. Nuclides of a given element that have different numbers of neutrons (but the same number of protons) are called isotopic nuclides or isotopes. For any particular element, only certain isotopes are stable. 27Al, with 13 protons and 14 neutrons, is stable. 28Al, with 15 neutrons, is unstable. A stable isotope is defined as an isotope for which no radioactive decay has been experimentally detected. Isotopes that are unstable are called radioactive isotopes (or radioisotopes). The term isotope applies equally to both stable and radioactive isotopes.

 The world that surrounds us, including the water we drink and the air we breathe, is mostly made of stable isotopes of the common elements, e.g., hydrogen, oxygen, and nitrogen. With the improvement in instrumentation over time, many isotopes that were once considered stable are now known to be unstable. They undergo radioactive decay, although with very long half-lives, and they are called long-lived radioactive isotopes. In natural terrestrial substances, a radioactive isotope with a sufficiently long half-life is said to have a characteristic isotopic abundance, and it may contribute to the standard atomic weight of an element if its isotopic abundance is sufficiently large. An example is calcium-40.

Of all chemical elements that have been discovered in nature (in contrast to elements that have been synthesized or produced by man), their natural terrestrial samples contain a total of 288 different nuclides. These nuclides originally were thought to be all stable isotopes until radioactivity for some was discovered. Two hundred forty-nine of these are in fact stable isotopes, but 39 have since been determined to be long-lived radioactive isotopes that have a characteristic isotopic abundance and contribute to a standard atomic weight. In addition, more than 3,000 other nuclides are known, and they correspond to radioactive isotopes of all elements, most with short half-lives.

 

The Periodic Table of the Isotopes

As part of the International Year of Chemistry (IYC-2011), IUPAC funded the effort to produce the IUPAC Periodic Table of the Isotopes (IPTI), which is shown in Figure 1 and is modeled after the Periodic Table of the Elements. While the Periodic Table of the Elements indicates the similarities in the chemical properties of the elements, the IPTI emphasizes the uniqueness of each element. Each element block of the IPTI provides the chemical name, the chemical symbol, the atomic number, and the standard atomic weight of that element. A color-coded pie chart displays all of the stable isotopes and radioactive isotopes having characteristic isotopic abundances that contribute to the standard atomic weight of an element. The mole fraction (or isotopic abundance) of each of these isotopes is depicted by the relative size of the pie slice associated with that isotope. The mass number of each isotope appears around the outside of the pie chart. Each mass number is shown in black for stable isotopes and in red for radioactive isotopes.

 The background color scheme used for cells of the elements on the IPTI depends in part on the number of isotopes that are used to determine the standard atomic weight of an element. If only one isotope is used to determine the standard atomic weight, the standard atomic weight is invariant and is given as a single value with an IUPAC evaluated measurement uncertainty, and the background color is blue. An example is aluminium with a standard atomic weight value of 26.981 5386(8), where the uncertainty in the last digit is indicated by the value in parentheses. If an element has no standard atomic weight because all of its isotopes are radioactive and, in natural terrestrial substances, no isotope occurs with a characteristic isotopic abundance from which a standard atomic weight can be determined, the background color is white. If an element has two or more isotopes that are used to determine its standard atomic weight and the variations in isotopic abundances and atomic weights in natural terrestrial substances are well known, the standard atomic weight is given as lower and upper bounds within square brackets, [ ], and the background color of the element is pink. An example is boron with a standard atomic weight of [10.806; 10.821], and this form indicates that atomic weight values are found in natural terrestrial substances as low as 10.806 and as high as 10.821 as shown in Figure 2. If an element has two or more isotopes that are used to determine its standard atomic weight, but the upper and lower bounds of the standard atomic weight have not been assigned by IUPAC or if the variations are too small to affect the standard atomic weight value, the standard atomic weight is given as a single value with an uncertainty that includes both measurement uncertainty and uncertainty due to isotopic abundance variations. The background color of such elements is yellow, and an example is osmium with a standard atomic weight of 190.23(3).


Figure 2. Variation in atomic weight with isotopic composition of selected boron-bearing materials from figure 5 of the document at http://www.ciaaw.org/pubs/TSAW%202009.pdf.

In a follow-on IUPAC project, an electronic version of the IPTI is planned in which a click on a chemical element cell by a user will open a form window to display additional information about the isotopes of that element. This window will include a table of the isotopes in natural terrestrial substances, their atomic masses, and their isotopic abundances. In addition, a figure will display all isotopes of that element, both stable and radioactive. The stable or naturally occurring radioactive isotopes with a characteristic isotopic abundance will be shown in the same color as they appear in the element’s pie chart. Other radioactive isotopes will be depicted in one of three half-life ranges: less than one hour, greater than one year, and the intermediate range between one hour and one year. To stress the importance of isotopes in our everyday lives and why teachers, students and the general public should be aware of isotopes, some applications of selected stable and radioactive isotopes will be provided in one or more of the following general categories:

Isotopes in industry
Isotopes in medicine
Isotopes in geochronology
Isotopes in earth and planetary science applications
Isotopes in forensic science and anthropology
Isotopes as sources for making new isotopes
Isotopes in biology

In each case, the application of a specified isotope will be described and often depicted pictorially. The scope of these applications will be vast and should impress readers with how often isotopes affect our daily lives.

An example of the applications of isotopes of the chemical elements is displayed in appendix A for the element fluorine. In this case, there is only one isotope, fluorine-19 (19F), that is stable and determines the atomic weight. The background color for the pie chart is blue and the single stable isotope of mass number 19 is shown in black. In the figure in appendix A displaying all of the isotopes of fluorine, note that only 19F has its mass number displayed in black. All other isotopes have their mass numbers displayed in red because they are radioactive. All radioactive isotopes of fluorine have a half-life less than one hour, except for 18F. They are shown on a white background because of their short half-life, whereas 18F has a dotted background because its half-life is between one hour and one year.

An example of the application of a fluorine isotope in everyday life is shown for 18F in the category of isotopes in medicine. It is used for imaging the organs, bones, tissues, and brain of the body in a technique called a Positron Emission Topography scan (PET scan).

An example of an 18F-PET scan is displayed (figure A1). In this scan, 18F is being used to observe the differences in brain activity between a sober and an intoxicated brain. With the half-life of 110 minutes, there is little chance of radiation damage to the patient because the amount of radioactive fluorine will decrease by a factor of about 104 within one day. Selected applications and selected uses of stable and (or) radioactive isotopes in our everyday lives for each of the chemical elements will be featured.

Appendix A
Example Element Page—Fluorine

fluorine

Stable isotope

Atomic mass*

Mole fraction

19F

18.998 403 22

1.0000

* Atomic mass given in unified atomic mass units, u.

 

Selected Applications of Stable and/or Radioactive Isotopes of Fluorine

Fluorine Isotopes in Medicine

1)      18F is a radioactive fluorine isotope that is used in a 18F-FDG compound (18 F- labeled, fluoro-deoxy glucose) for imaging the organs, bones, tissues and brain of the body with a technique called a Positron Emission Topography scan (PET).

   a.  18F emits positrons (positive electrons) that collect in tissue and interact with regular negative electrons when injected into the body. The positrons and electrons annihilate each other, producing two gamma particles that are emitted in opposite directions and this causes the release of X-ray-like radiation. The radiation is detected on a PET camera, which generates a picture of the body part being examined.
   b.  Because 18F has a short half-life of about 110 minutes, there is little chance of radiation damage to the patient.

Figure A1: An 18F-FDG PET scan is used to observe the differences in brain activity between a sober and an intoxicated brain. (Image Source: National Institute on Alcohol Abuse and Alcoholism (NIAAA)).

 

References

Fluorine

Fluorine Isotopes in Medicine

  1. Krebs, Robert, 2006, The history and use of our earth’s chemical elements: a reference guide, Westport, CT: Greenwood Press.
    1. Fluorine. Chemistry Explained: Foundations and Applications. Advameg, Inc., 2011. Web. 03 Nov. 2011. Retrieved from website: http://www.chemistryexplained.com/elements/C-K/Fluorine.html
    2. RadioIsotopes in Medicine. World Nuclear Association. Web. 02 Nov. 2011. Retrieved from website: http://www.world-nuclear.org/info/inf55.html
    3. Mausner, Leonard F. QA issues in radioisotope production for nuclear medicine. Brookhaven National Laboratory, 08 November, 2007. Web. 03 Nov. 2011. Retrieved from website: http://www.asqlongisland.org/seminars/LM_Amer_Soc_for_QA_talk_11_8_07.pdf

Figure 1:  Thanos, Panayotis K., Wang, Gene-Jack, and Volkow, Nora D. POSITRON EMISSION TOMOGRAPHY AS A TOOL FOR STUDYING ALCOHOL ABUSE. National Institute on Alcohol Abuse and Alcoholism (NIAAA). Web. 03 Nov. 2011. Retrieved from website: http://pubs.niaaa.nih.gov/publications/arh313/233-237.htm

Element Page Last Modified: May 4, 2012

Comments

isotopes paper

Interesting project! The new view on variable natural abundance and its implications for atomic weights is clearly an advance in our understanding. (How we should incorporate this into classes, especially for beginners, will take some time to figure out.)

A couple of questions...

1.

Has the decay of Ca-40 been demonstrated (or simply predicted)?

If so, do you happen to have a reference? If not, is there some good discussion of the limitations of measuring such long half lives? (I know the work that measured the decay  of Bi-209; its half life is about 1/100 that of Ca-40.)


2.

The Appendix is neat. I hope this will become something of an open-ended project, to add more and more of these.

I was disappointed with the info shown there about the isotopes. You group the half lives into only three bins! That loses a lot of interesting info. (Half lives range over ~35 powers of ten. Amazing range.) Even your example of F-18... Its use depends on the half life being near the low end of its bin.

Rather than quibble about how they should be binned... Would you consider something like... a bar graph, where the height of the bar for each isotope reflects the half-life, on a  log scale. Perhaps the bar width could reflect the abundance (with dotted bars for isotopes with no natural abundance). I haven't thought it through much, so this is just a first pass idea, with  the goal of presenting more info -- interesting info -- in a simple visual format.


regards,

bob

periodic table of the isotopes

Bob;


Thanks for your comments.


Raising the issue of half-lives and whether an isotope is stable or unstable, you give me an opportunity to mention a lively discussion that our whole Task Group participated in recently that lasted for over a period of months. We originally had selected a half-life on the order of 10 billion years (a time on the order of the age of the earth) as the defining line to distinguish between stable and unstable isotopes. Some Task Group members felt that this was an arbitrary number and we should instead select as a criterion a number that was not arbitrary. After trying and failing to find such a number, we selected our present criterion. A stable isotope is defined as an isotope for which no radioactive decay has ever been experimentally detected. A unstable isotope is energetically unstable and will decay over time.


The source of all half-life values used to create the Table is the review article "Table of the Isotopes" published in the CRC Handbook of Chemistry and Physics. For more than two decades, I have searched the scientific literature, evaluated the reported values and recommended what I consider the best number for each of the various properties of the isotopes, mass, half-life, alpha, beta, gamma ray energies and intensities, spin. parity, magnetic dipole and electrical quadrupole moments. 


We do not use theoretical estimates of the half-lives in this Table, although Ca-40 is theoretically unstable via decay to Ar-40. With respect to the Ca-40 value that you mention, the half-life experiment dealt with the Ca-40 double beta decay (double electron capture in this case). It was published more than a decade ago in the Russian journal 'Particles and Nuclei Letters' by the Joint Institute for Nuclear Research (JINR) in Dubna. There has not been another experiment reported on this decay since that time. As a result, I have not had occasion to re-examine that paper in more than ten years. As a direct result of your question, I took a quick look at the paper again this morning. This paper may have presented an upper limit to a half-life value rather than a half-life value. If this turns out to be true, we will change the color of the mass number 40 in the calcium pie chart from red to black to indicate that Ca-40 is stable. This question will be addressed immediately after this Virtual Colloquium is over.


You mentioned the appendix of the paper. We indeed already have appendices for all 118 elements and most of these appendices do show applications of the isotopes of these elements. The exceptions are some of the very heaviest elements, whose half-life values are in milli-seconds or micro-seconds range and no applications have been found as yet, due to their very short half-life and their recent discovery.


In answer to your question, this is an open-ended project. We are planning to provide an electronic version of the Table where electronic links to each element will provide the appendix of information as shown in the case of fluorine. Ty also mentioned in an earlier response that we are planning a follow-on project in which online applications will be developed, as well as teacher classroom aids and Professor Peter Mahaffy of King's University College in Edmonton, ALberta, Canada will have a leading role.


As far as the lack of more detailed information on isotopes in our Table is concerned, IUPAC does not deal directly with this information. The review article in the Handbook of Chemistry and Physics is not related to any IUPAC activity. Our Task Group's interest in developing this Project was to introduce students, teachers and the general public to the concept of isotopes. In the future, we could probably provide links to more detailed information on isotopes and let any interested readers follow up on their own.


Once again, thanks for your interest and your comments.


Norman

boron isotope variation in sea water vs. evaporated sea water

Norman and Tyler,

Can you help me understand figure 2? Specifically, the comparison of sea water to evaporated sea water.  What does the dot on sea water mean? You have two scales on top, atomic weight and mole fraction, and I am confused as to what is being represented.  Are you saying the variance between samples of evaporated sea water is greater than sea water, and evaporated sea water tends to have more of the heavier isotope?  Does this variance deal with differences in the enthalpy of vaporization and the way the water was removed?  I am very curious about what is being shown here.


Thanks,
Bob

 

 

boron isotopic variation in sea water vs evaporated sea water

Bob,


You have hit upon a most important topic. Stable isotopes are fractionated by physical and chemical processes and that is why they are of substantial use for investigations in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic applications, geochemistry, geology, oceanography, and paleoclimatology. The wide range of isotopic variations in 20 elements in naturally occurring materials is highlighted in the publication "Compilation of Minimum and Maximum Isotope Ratios of Selected Elements in Naturally Occurring Terrestrial Materials and Reagents" (see http://pubs.usgs.gov/wri/wri014222/). This is a very popular reference for graduate student education. As an example of important processes, when water evaporates , the lighter isotopes, hydrogen-1 and oxygen-16, are preferentially enriched in the vapor; thus, the remaining water is enriched in deuterium and oxygen-18. In like manner, when condenses from moisture in a cloud and falls to Earth, it is enriched in oxygen-18 and deuterium relative to the moisture in the cloud. These differences arise from differences in vapor pressure (or zero point energies) of the different isotopologues. This "distillation" effect enables isotope hydrologists to differentiate environmental waters from various sources. In the case of boron, when ocean water evaporates, boron-bearing salts precipitate and these salts are preferentially enriched in the light isotope of boron (boron-10) by a factor of 1.03, enriching evaporated ocean water in the heavy boron stable isotope. This seems like a small fractionation factor, but isotope-ratio mass spectrometers can commonly differentiate samples at the 0.0005 level or better.


Regarding the solid black dots, these are internationally distributed isotopic reference materials, and this should have been mentioned in the figure caption.


Ty

Answered it myself

OK, I think I answered the first part of the question myself, in that the bar line represents variance in mole fraction of 11-boron, which in a two component system gives the mole fraction of the only other isotope, and thus results in the associated atomic weight.  So both scales essentially say the same thing, and the molar mass would increase if the lighter isotope vaporizes faster than the heavier.  Is that what is going on?

Answered it myself

Bob,


You are on the right track. The boron does not evaporate, rather it precipates into a boron-bearing mineral and boron-10 is enriched in this mineral.  See my previous response.


Thanks,


Ty

Periodic Table of Isotopes for the Educational Community

 

This message is being forwarded from Eric Scerri:

Now that more general educational aspects are being discussed can I run the following version which I teach to my students past experts and educators for comments.

It's something that does not seem to get into many textbooks but I believe is rather important concerning binding energy and the choice of 12C as the standard.

----------------------------------------------------------------------------------------------------------------------------------------------

Binding Energy
1. For all but the lightest nuclei, the BE per nucleon is above 7.5 MeV. From there to
the end of the periodic table, the BE varies only from 7.5 to 8.8 (peaking at Fe/Ni.)

2. This BE reduces the Mass of a (free) nucleon from its free value by about 0.8%, a
reduction that occurs in all but the lightest nuclei. A mass standard MUST have this
average BE/nucleon included if isotopic mass numbers are going to be close to the
actual masses.*

3. Therefore the ATOMIC mass of any single isotope could be used as a standard as
long as it is not one of the first elements. 12C is chosen due to the predominance of C in
carbon compounds the most common of all compounds.

Now a little story (first told to me by radiochemist, Lee Sobotka)
Image you build 120Sn from 50 separate protons (which you take from your "p" jar on
your chemistry lab shelf), 50 e- (taken from the wall plug) and 70 n's (taken from some
other source)

You do this atom building on a balance. You put them together on the balance and you
end up with a mass of 119 neutron masses. You are convinced you dropped one
nucleon on the floor. You search but don't find one. You deconstruct and find all 120
nucleons (and the 50 e-). You reconstruct and again you get 119 n masses. Look again
on the floor and again find nothing. After doing this x times - Einstein, who is looking
over your shoulder, gives you a dope slap. Finally you get it.
0.8% of 120 = .96

The "lost" nucleon is due to binding energy.

If we had used n = 1 = p as our standard the weight of the isotope should have
been 120. In fact it is closer to 119 due to binding energy.
Isotopic mass number = 120 but actual mass = 119.

By using the a.m.u. based on 12C which has the 0.8% BE built-in we get a result of
120 ! Remember the amu is smaller than the p or n mass.

If we use the n or the p as the standard the masses do not correlate with the
actual masses and typically differ by 1 even for medium-sized isotopes such as
120Sn
--------------------------------------------------------------------------------------------
eric scerri

Please also see ericscerri.com/

for educational resources on elements, the periodic table and philosophy of chemistry.

 

Periodic Table of Isotopes

Eric:


Your note about the binding energy, or mass defect as it was originally called, does cause the mass of the nucleus of an atom to be less than the masses of the individual protons and neutrons making up that nucleus. In an article on atomic weights and the atomic weight commission (Chem Int 6 (1), Jan/Feb 1984 and Chem Int 26 (1) Jan/Feb 2004) I mentioned in a discussion about the atomic weight standard debate between Dalton's choice of H=1 and O=16 that the H=1 value would lead to a discrepancy of the atomic weight of heavy elements and their mass number. As an example, uranium would have an atomic weight of 236 and not 238 on a scale of H=1. This is a reflection of the binding energy effect as you have noted.


I would note that your use of the symbol amu (for atomic mass unit) is incorrect. The symbol amu was the mass unit on the oxygen=16  mass scale. When the scale was changed to carbon-12 = 12, the atomic mass unit was changed to the unified atomic mass unit (symbol u).


As noted earlier, in the first decade of the twentieth century, the choice of O=16 was selected over H=1. In 1929, the two isotopes of oxygen were discovered, O-17 and O-18. As far as the standard was concerned, the chemists stayed with the previous choice of natural oxygen = 16, while the physicists used the standard of 16 for the isotope, O-16, which is the mass that they measured in their instruments. This discrepancy in the standard continued from 1929 to 1961 when the standard of carbon-12 = 12 was agreed upon by both IUPAP and IUPAC. Since the two discrepant mass standards were now unified, the name and symbol were appropriately changed. In the articles that I mentioned above, I describe the details of how the problems and the solution of the mass scale came about.


Before the final choice of carbon was made, there were a number of suggestions put forth. They were all rejected either by the chemists or the physicists. However, in the days when oxygen = 16 was the standard, carbon = 12 was always a secondary standard for mass spectroscopists. For chemists, whatever choice would be made had to cause only a minor change (within experimental uncertainties) to all previous chemical measurements. Carbon was found to be acceptable to both the chemists and the physicists.


Thanks for your comment,


Norman

IUPAC Periodic Table of the Isotopes for the Edu Community

Dear Ling,


Regarding the selection of an atomic weight (relative atomic mass) to use for chemical calculations, I like your statement, "Or should we in fact look at the distribution of values within the range and based upon that distribution find the acceptable point?"  For education, this is a good choice it seems to me. For pure numerical calculations I do not have heartburn over the use of 12.01 or 12.011.



The lowest carbon-13 abundance at present is 12.009 662, which was reported in 2000 on crocetane (2,6,11,15-tetramethylhexadecane) produced at cold seeps of the eastern Aleutian subduction zone. In the next few decades, a lower atomic-weight value may be reported. The Commission may in the future decide to review carbon again, and at that time re-evaluate the lower and upper bounds of the interval for carbon. However, just because a lower atomic-weight value is published and reported to the Commission, the interval will not spontaneously be updated. Updating requires an IUPAC project that performs a literature review and in-depth evaluation.



Regarding your question, "In your article for carbon ’the uncertainty of the delta measurement’ = 0.000003. Where does this number come from? Who chose and why 0.000003?". This is the uncertainty of the delta measurement is that published by the author of the delta measurement, and from this we calculate an atomic-weight uncertainty.



Now, where does the 0.000 027 come from. This uncertainty is due to mismatch between the isotopic abundance (or atomic-weight scale) and the delta scale. It comes from the uncertainty of the "best" measurement of isotopic abundance, which is published by the Commission in it Table of Isotopic Compositions of the Elements. The most recent of which (2009) is found here http://www.ciaaw.org/pubs/TICE2009.pdf. Let's do a back of the envelope calculation that will be close, but not exact because the best measurement of carbon was performed on a material that was not at the zero point of the delta scale. Referring to the Table of Isotopic Compositions of the Elements, one finds that for the best measurement of carbon, the mole fraction of carbon-13 = 0.011 078(28) and the mole fraction of carbon-12 is 0.988 922(28). Now we need the atomic masses of carbon-12 and carbon-13, and these are found at http://www.ciaaw.org/pubs/Atomic%20Masses.xls, and we find: carbon-12 = 12 u and carbon-13 = 13.0033548378 u. Now calculate the atomic weight of a sample with a mole fraction of carbon-13 = 0.011 078 and we get 12.011115164893. Now calculate the atomic weight for a specimen with a carbon-13 = 0.011 078 - 0.000 028, which is 0.011 05, and the atomic weight is 12.011087070958. The difference between the two atomic-weight values is 0.000 028, which is satisfactorily close to 0.000 027 for this back of the envelope calculation.



You have picked up on an important point that usually the delta measurement uncertainties are an order of magnitude smaller that the "best" measurement uncertainties, and in most cases can be neglected because the biggest effect is usually the rounding down for the lower bound and the rounding up for the higher bound. The aim is to ensure that the atomic-weight interval will include the atomic weight of any natural material that might appear in a chemistry laboratory, and this is accomplished by an in-depth evaluation of the published literature.



Thanks for your interest.
Ty

Re: measuring uncertainty

Dear Tyler,

Thank you for your reply and answering my questions. I will still use webelements but also use your work and reference your work when teaching this subject material in any relevant course. It's very interesting. I hope the rule for truncation for the lower bound and the adjustment for the upper bound is used so that these uncertainty measures have some bearing on the results o/w you may find that the results are the same if the rules are carried out directly on the lowest measured and highest measured abundances (as in the case for carbon).

Thank you again,

Ling

Ling Huang, Sacramento City College

   

 

 

PhET Isotope Simulation

The IUPAC periodic table of isotopes is a great resource for the educational community.

I wanted to mention another educational tool that could be of interest. Last year, I designed an interactive simulation about isotopes as part of the PhET project.

http://phet.colorado.edu/en/simulation/isotopes-and-atomic-mass

In the 'Make Isotopes' tab, students can add and remove neutrons and observe the effect on the mass number and stability.

In the 'Mix Isotopes' tab, students can add and remove isotopes of an element and observe the effect on percent composition and compare to 'nature's mix' of isotopes.

We used atomic weights and isotopic compositions from NIST, but we could rewrite the code to use the IUPAC data.

The IUPAC project could embed this simulation as a supplement to the online materials. We could also provide a link to the IUPAC periodic table on the PhET website to reach more educators.

Also of potential interest to the IYC community, the PhET project has a tool that allows volunteers around the world to translate our simulations. The isotopes simulation, for example, has been translated into 32 languages.

If you have any questions or comments, you can contact the PhET project directly at: phethelp@colorado.edu

IUPAC Periodic Table of the Elements for the Edu Community

Dear James,


This is an extremely important question, and I am very glad you asked it.


The Commission believes that it would be excellent if Johnny or Susan were to come to you and say, “Dr. Stevenson, what value am I supposed to use for the atomic weights of carbon and oxygen in question 3?”. This gives you the opportunity to open a discussion with your students about isotopes and their affect on the atomic weights of the elements. You could present Fig. 2 (variation in atomic weight with isotopic composition of carbon-bearing materials) and Fig. 7 (the equivalent figure for oxygen) found at http://www.ciaaw.org/pubs/TSAW%202009.pdf. You could ask them to refer to these figures and find and use for hypothetical question 3 the atomic-weight values for carbon and oxygen of carbon dioxide in air because both are presented in these figures, and they both have a relatively small range.


In the same document referred to above, the Commission also provides a Table of Standard Atomic Weights Abridged to four significant figures (see page 387) and one abridged to five significant figures on page 390.


In the situation that one has no knowledge of the material, such as for trade and commerce, one can go to Table 6 on page 393 of the document above and use the conventional atomic-weight values presented.  For example, carbon is 12.011 and oxygen is 15.999. The Commission would hope that using values from this table is a last resort. It provides the minimum educational value.


Thanks again for this question.


Ty

Calculation of molar mass

Hi,

Thanks for the interesting information. Your title indicates that this is for the educational community.

So if I want the students in general chemistry, who are just learning about stoichiometry, to calculate the number of moles of carbon dioxide in a certain mass of the compound what should I expect them to use as the molar mass of carbon dioxide if they have been given this periodic table?

It would seem to me that one value for carbon and one value for oxygen would be beter for the novice.

 

Thanks,

James Stevenson

IUPAC Periodic Table of the Elements for the Edu Community

Dear James,



This is an extremely important question, and I am very glad you asked it.
The Commission believes that it would be excellent if Johnny or Susan were to come to you and say, “Dr. Stevenson, what value am I supposed to use for the atomic weights of carbon and oxygen in question 3?”. This gives you the opportunity to open a discussion with your students about isotopes and their affect on the atomic weights of the elements. You could present Fig. 2 (variation in atomic weight with isotopic composition of carbon-bearing materials) and Fig. 7 (the equivalent figure for oxygen) found at http://www.ciaaw.org/pubs/TSAW%202009.pdf. You could ask them to refer to these figures and find and use for hypothetical question 3 the atomic-weight values for carbon and oxygen of carbon dioxide in air because both are presented in these figures, and they both have a relatively small range.



In the same document referred to above, the Commission also provides a Table of Standard Atomic Weights Abridged to four significant figures (see page 387) and one abridged to five significant figures on page 390.



In the situation that one has no knowledge of the material, such as for trade and commerce, one can go to Table 6 on page 393 of the document above and use the conventional atomic-weight values presented.  For example, carbon is 12.011 and oxygen is 15.999. The Commission would hope that using values from this table is a last resort. It provides the minimum educational value.



Thanks again for this question.



Ty

Important data, teachers can think how to use it

Hi,

I agree with James and Ling Huang that the webelements site provides enough information and that most of the high school students and teachers I know use this site. But I think that the table presented here by Norman and Tyler represents the idea of isotops in a very good way. Students are very interested in radioactivity, and the concept "isotops" could be clearer with this representation. I would like this table to be in my class.

We are talking now about spreading the idea that chemistry is important, relevant and not scary. Talking about the benefits of radioctivity fits perfect this goal. It is important to have a reliable source as IUPAC and I think that teachers can use the data in the site for different educational purposes. I would be happy to ask my students to use the data from IUPAC and even talk about the importance of using data from such a reliable source as IUPAC instead as from webelements.

I think that IUPAC should have a site like webelements, or collaborate with such popular sites as ChemSpider, etc. (maybe they collaborate?).

It would be nice to have an application for smartphones. 

It was interesting to hear about Ca in milk.

Malka

 

IUPAC Periodic Table of the Elements for the Edu Community

Dear Malka,


I have no idea about a collaboration of IUPAC with webelements.com or other sites, but I can comment on an application for smartphones and other electronic devices. In a follow-on IUPAC project, it is planned than online applications will be developed. Prof. Peter Mahaffy of King’s University College in Edmonton, Alberta will be a leader in the campaign on this activity.


Ty

Interactive periodic table

Thanks, Malka and Ty,

Yes, at the King's Centre for Visualization in Science (www.kcvs.ca) and the IUPAC Committee on Chemistry Education, we are planning a follow-up project to create an on-line, interactive version of the IUPAC Periodic Table of the Isotopes.  We have also been turning many of the other digitial learning objects on our kcvs site into aps both for the i-pad and android devices, and hope to eventually do so for this project as well.  The following paper in this ConfChem discussion, on Visualizing the Science of Climate Change, gives examples of work that we are doing at KCVS in collaboration with IUPAC, UNESCO, and others.

Peter Mahaffy

Information on Webelements website

Hi Tyler

I have forwarded the information to Dr. Mark Winter at the Dept. of Chemistry of the University of Sheffield, UK, since I have nothing to do with their website.

If you do a GOOGLE on ‘periodic table’ the first hit that shows up is WebElements (www.webelements.com). If you do a GOOGLE on ‘periodic’ the first hit that shows up is WebElements. If you do a GOOGLE on ‘elements’ the first hit that shows up is WebElements..... If some of their information is out of date  then it would be a good idea to notify Webelements, since it is the 1st hit on Google etc. for many searches (indicating many people use the site for info).

In your comments I am not sure if you have looked at webelements isotope information. If you do not click their top buttons then general information is given for each element. For Boron for example in your comment 2 it suggests webelements do not have information on Boron 10/11 but you need to click their button on the top under isotopes for that information (before clicking on Boron). In your comment 6 you mention about the names and symbols for the two new elements named earlier this week, that is, flerovium (Fl) and livermorium (Lv). This is included in their first webpage (scroll down) and they have a link also containing info on flerovium and livemorium.

It may be that webelements needs to update some of their information (more accuracy to a given decimal place, indication of lower/upper bound information etc., an update link for new information.  Hence I forwarded the information to webelements.

Thanks.

Ling

Ling Huang, Sacramento City College

IUPAC Periodic Table of the Isotopes for the Educ Community

Dear Ling,


Thanks for forwarding information to webelements.com.


I am familiar with isotopes on their Web site. That is how I determined that they were not aware of the fact that calcium-40 is radioactive.


Thanks,


Ty

IPTI

Norman and Tyler,

Thank you for this excellently written article on the IUPAC Periodic Table of Isotopes. It seems to me that you are concerned there may be many misconceptions with educators understanding of the periodic table, and I think this is a valuable resource for many of us. Here area few things that came to mind while reading your article.

1. On page 2 (I like to print the pdfs) you state the standard atomic weight is dimensionless, sort of like a specific gravity versus density.  We sort of say the same things through our definition of the amu, but I have never thought about it in this light, and have never called it dimensionless.  Why do you take this approach?

2. You bring forth that standard atomic weights should not be considered as constants of nature, and provide a historical background to this.  When did you start using intervals to describe standard atomic weights? From this link I am thinking 2009? http://www.ciaaw.org/pubs/TSAW%202009.pdf

3. This is the part that I am most curious about.  You use intervals to describe geographical (location-based) variance, but you do not do so to describe temporal (time-based) variance. For example, in my classroom's periodic table Radon's molar mass (yes, that is what I like to call it), is in parenthesis, and I ask my students why they think that is?  We then discuss the uncertainty of the isotopic composition between different samples resulting from varying mole fractions with different lifetimes, and thus there is not an exact value. I now realize I may have not quite had that right, and that I should also be saying the same sample (and it is different between different samples).  On page 4 you state, "the IPTI emphasizes the uniqueness of each element", but then for elements like Radon you leave them as a complete blank.  Why?  Isn't there a way to describe the uniqueness of different samples of Radon, like there is for Boron?

Let me build on this a bit more. I recently attended an information sciences workshop on "Ontologies," where the periodic table was given as an example of an ontological framework where knowledge could be represented through universal representations (like every atom has X (protons), Y (neutrons),....).... Which then layers to standard atomic weights resulting from isotopic distributions in a sample of those atoms..., and we appear to stop there.  Why must Radon be a blank? Even if the atomic mass of a sample changes with time, isn't there a way to describe that with "universals" (like mole fraction and half life)? If nothing else, wouldn't it be bounded by the lightest and heaviest isotope? My question is that it appears the IPTI has extended the ontological framework of the periodic table to cover location based variance in isotopic composition between samples, why can't it be extended to temporal variance?

I haver really found this to be a stimulating and interesting paper to read, thank you.

Bob

 

 

 

The Periodic Table of Isotopes for the Educational Community

Bob, 


Thanks for your kind and interesting comments. 


Regarding your item 1, the masses of the nuclides commonly are expressed in unified atomic mass units (symbol u). The dalton (symbol Da) is an alternative name for unified atomic mass unit as you know. Both have the value 1.600 538 782(83) × 10E–27 kg.  


Atomic weight is another name for relative atomic mass. From the adjective “relative,” one can infer that the quantity is dimensionless. This comes about because atomic-weight values are scaled to an unbound neutral carbon-12 atom in its nuclear and electronic ground state, which, by consensus (for the last four decades), has a mass of exactly 12 u.  The atomic weight of an element in any particular sample is calculated from the sum of the products of the atomic mass and the isotopic abundance (mole fraction) of each stable or selected radioactive isotope of that element in that sample and expressed relative to 1/12 the atomic mass of carbon-12. Consider a boron-bearing specimen with isotopic abundances of boron-10 and boron-11 atoms of 20.5 % and 79.5 %, respectively. The atomic weight of this specimen is (10.012937 u × 0.205 + 11.0093054 u × 0.795) / (1/12 × 12 u) = 10.805, where u is unified atomic mass units. It is dimensionless because mass over mass cancels. 


Regarding item 2, you are correct. The Commission on Isotopic Abundances and Atomic Weights first started using intervals as standard atomic weights in its 2009 Table of Standard Atomic Weights, announced December 2010. 


Regarding item 3, for many elements having only radioactive isotopes, each specimen from a natural terrestrial source can have a substantially different isotopic abundance depending upon the source of the material. And for radon (note, element names are always lowercase unless they are the first word in a sentence), various specimens can have greatly different isotopic compositions depending upon the source of the material. For radon and similar elements having only radioactive isotopes typically with shorter half-lives, we say that the element does not have a characteristic isotopic composition from which a standard atomic weight can be determined. However, there are four elements that have only radioactive isotopes, and they have characteristic isotopic compositions in natural terrestrial samples because the half-lives of some of their isotopes are sufficiently long. These elements are uranium, thorium, protactinium, and bismuth and for these elements a standard atomic weight can be determined. 


Getting back to radon, the Commission provides a table titled “Relative atomic masses and half-lives of selected radioactive isotopes.” This is table 3 on page 384 in the 2009 report (http://www.ciaaw.org/pubs/TSAW%202009.pdf ). For radon, the mass number, atomic mass, and half-life of radon-210, radon-211, and radon-222 are given. There is no general agreement on which of the isotopes of radioactive elements is, or is likely to be judged, “important”. It should be pointed out that various criteria, such as “longest half-life”, “production in quantity”, and “used commercially”, have been applied in the past to the Commission’s choice. 


The IUPAC project task group members are creating so-called element pages for each of the isotopes, such as shown for fluorine in our paper. We will provide similar element pages for radon and other elements having no standard atomic weight. We will present their radioactive isotopes and discuss at least one application of isotopes of the element if possible. 


Ty


 

May 31 IPTI

All,

The authors of this paper have graciously provided a high resolution PDF downloadable copy of of the May 31, IPTI, which we have posted near the top of this paper (titled ipti_2012-05-31.pdf).

Thanks,

Bob

Periodic Table of Isotopes for Educ. Community

Dear Ling,


This is a great question.  I had not been on www.webelements.com for some time, but your question gives me the opportunity to do so.


1.  Looking at boron, for example, I see that webelements.com lists 10.811 (7) as the atomic weight (sic). The value of 10.811 (7) is not the atomic weight, rather it is the standard atomic weight. The difference between “atomic weight” and “standard atomic weight” is that the atomic weight of a specified material is determined from the isotopic composition of boron in a specified specimen, whereas the “standard atomic weight” is the best knowledge of atomic weights of an element in natural terrestrial sources of that element. As opposed to the standard atomic weight, the atomic weight of a specific sample of boron easily can be determined to 6 figures by measuring its isotopic abundances. For example, the atomic weight of boron in a sample from the Victorian volcanic-crater lakes of southeastern Australia was 10.8207 (see page 1994 of http://ciaaw.org/pubs/SNIF.pdf ).


2.  The webelements.com value of 10.811 (7) suggests to many students and teachers that the standard atomic weight of boron is a constant of nature. Such is not the case. The atomic weight of boron varies in natural terrestrial materials because boron has 2 isotopes, boron-10 and boron-11. The atomic weight of boron in a boron-bearing substance depends upon the isotopic abundances (mole fractions) of the stable isotopes boron-10 and boron-11 in that substance (see figure 5 of Table of Standard Atomic Weights 2009 at the URL http://www.ciaaw.org/pubs/TSAW%202009.pdf ).


3.  The webelements.com value of 10.811 (7) is incorrect because it is out of date. This value is the value from the 2007 Table of Standard Atomic Weights.  webelements.com has missed the IUPAC press release 18 months ago (December 2010) and the publication of the Table of Standard Atomic Weights 2009 that the standard atomic weight of boron (and 9 other elements, H, Li, C, N, O, Si, S, Cl, and Tl) have been changed to intervals to alert teachers and students that the standard atomic weight of boron is not a constant of nature.  (See http://www.ciaaw.org/pubs/TSAW%202009.pdf ). Because these isotopic variations are well know for 10 elements, the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) has given their standard atomic weights as lower and upper bounds within square brackets, [ ]. For boron, this is [10.806; 10.821].


4.  Thus, if webelements.com wants to be current, it needs to update the value of the standard atomic weight of boron to [10.806; 10.821] and provide information to students and teachers that standard atomic weights of many elements are not constants of nature and that the atomic weights vary in natural terrestrial substances.


5.  webelements.com has failed to pick up on the fact that many of the isotopes used to determine the standard atomic weights of the elements are not stable, but radioactive. Take a look at calcium-40 on the latest IUPAC Periodic Table of the Isotopes (dated May 31, 2012) and found at http://ciaaw.org/pubs/Periodic_Table_Isotopes.pdf . One observes that the major isotope of calcium (calcium-40) is radioactive as indicated by the mass number 40 given in red. This information gives teachers the opportunity to educate students and inform them that the milk they are drinking at lunch is radioactive. My daughter Sara was amazed at this when she updated the IUPAC Periodic Table of the Isotopes and found that the milk she gives to her daughter Chloe (www.chloeglidewell.com ) is radioactive.


6.  I would also like to point out that the latest IUPAC Periodic Table of the Isotopes (dated May 31, 2012) and found at http://ciaaw.org/pubs/Periodic_Table_Isotopes.pdf lists the names and symbols for the two new elements named earlier this week, that is, flerovium (Fl) and livermorium (Lv).


7.  The backgrounds of the 10 elements assigned intervals as standard atomic weight values in 2009 are pink on the IUPAC Periodic Table of the Isotopes to highlight these elements.


8.  Teachers are encouraged to print the IUPAC Periodic Table of the Isotopes in large poster size and place it beside the Periodic Table of the Elements in chemistry classrooms and laboratories.  If you don't have the capability to a print large poster, please send me an email at tbcoplen@gmail.com, and I will see what I can coordinate.


Thanks Ling for this interesting comment,


Ty


Tyler Coplen


 

Periodic Table of Isotopes for Educ. Community

As a lurker on this conference but only an occasional participant I do feel motivated to make a comment here since I am WebElements. I am very well aware of the isotopes project and let me state now that the project is very interesting. I saw Ling's question and was tempted to answer it myself at the time but it is exam season here and most waking hours involve marking and so lacked the time. I am grateful to colleagues at this conference who wrote to me independently telling me about Tyler's comments on WebElements, which as it happened I had already seen. They do seem to be rather a diatribe don't they? Therefore please allow me correct one or two misunderstandings that Tyler may have.

I did have a quick look around some of the other periodic table sites and none of the major ones (?) include the ranges. Neither does NIST so far as I could see having looked rather quickly. Even the fount of all knowledge, Wikipedia, doesn't. 

I try to keep WebElements current, and Tyler may or may not remember that he kindly sent me an electronic version of a prepublication list of atomic weights in 2001 which WebElements published therefore in a timely fashion. What Tyler does not know because as he didn't check before committing his comments is that WebElements is undergoing a restructuring at present and this is taking some considerable time. The reasons for the over long development time don't matter, but availability of time and the word "structural" should make the reasons clear. I should like to think I will have the structural revamp of WebElements in place by the end of the northern hemisphere summer, but we'll have to see (you will see this a major structural change and then a series of content enhancements). So I should like to reassure Tyler that, yes, the values are out of date, currently, but "has failed to pick up on the fact that many of the isotopes..." is just wrong. The new values are in the WebElements database and have been for months, and will appear in the revamped version. And I am aware of 40K. And the new element names appeared 5 months ago at the start fo the naming process just completed. Other colleagues around the world who have been kind enough to send me datasets, sometimes pre-publication, will similarly see their data updated.

I don't think Tyler's response quite answered Ling's original question as I understood it. The current version of WebElements is weak on isotopes as it breaks the data into "naturally occurring" and "radioactive" (but only a selection of the latter). This will be fixed in the next WebElements. In addition, WebElements does include a few uses of a few isotopes, but not in anything like the detail indicated in Appendix A for 18F. In response to a different question, I should be very interested in including at least paraphrases of some of the forthcoming IUPAC material (licensing/permissions permitting), because this will help get the message across to more people, more so than IUPAC can do itself easily as the Webelements web reach is much wider. I should also be interested in collaborating on a poster if appropriate.

Maintaining any database or web site is a task and quite apart from the errors in WebElements (thanks to the multitudes sending in reports, they will be acted upon) even IUPAC has errors. I just noticed the pdf at http://www.iupac.org/fileadmin/user_upload/news/IUPAC_Periodic_Table-201... has just one URI on it and that is wrong ( http://www.iupac.org/reports/periodic_table/ ), but my mother would tell me that it would be impolite to make such a point in public.

I do have a minor question of my own that I had intended to ask when I first saw the data but never got around to asking. Why use ; to indicate bounds instead of -, especially as ; is a common item delimiter in some countries (which maybe is not quite the sense in which the ; is being used)? My instinct, flawed possibly, is that a hyphen probably gets the message across to more cultures than a ; (?)

Back to marking and then revamping hopefully.

 

Response on WebElements

Mark,
You are correct, I now remember our correspondence about the 2009 Table of Standard Atomic Weights. You point out correctly that neither NIST nor Wikipedia highlights intervals for standard atomic weights. For NIST, this is not surprising because NIST moves slowly. Several months ago when I looked at some elements on Wikipedia, I noticed that standard atomic weights were not dimensionless, but were given with the unit u. So I don't give Wikipedia high marks for always being correct.



I would encourage WebElement.com to be among the first to point out that atomic weights are not constants of nature for many elements. WebElements.com could be a primary educational leader on atomic weights in this fashion. If students easily could see a plot of atomic weight variation for selected substances for H, B, Li, etc, this would be excellent.



I wish you the best on updating Web pages because it is not the easiest thing to do.
Ty

Periodic Table of the Isotopes

Mark:


Your early comments deal with responses that Ty made about WebElements, so I will leave those for Ty to address the next time he has access to a computer (he is on a trip at the moment).


I will respond to your question about our notation for intervals in our publications. Your suggestion to use a hyphen, -, to indicate bounds is wrong. The hyphen, as in a - b, actually indicates a range. Its meaning is the difference between a and b. The range of the atomic weight interval of carbon is 12.0116 - 12.0096 = 0.0012. The interval of the atomic weight of carbon is [12.0096; 12.0116]. This indicates that the atomic weight of carbon will be greater than or equal to 12.0096 and will be less than or equal to 12.0116. This interval includes both the lower and the upper bounds.


The source for this notation is in VIM, the international vocabulary of metrology, see JCGM 200:2008, International vocabulary of metrology - Basic and general concepts and associated terms (VIM, 3rd edition), http://www.bipm.org/publications/guides/vim.html.


I hope that this explanation will clarify the use of our notation for you.


Norman 


 

Interval

Very helpful Norman, many thanks for the reply, I wasn't aware of that VIM document, and I am now clearer about this.

Sorry, hadn't intended the hyphen to be a suggestion, I was seeking clarification. I guess I was using (very loosely) the - to mean the spoken "to", as in a to b, and of course you are correct about "range".

It looks like the URL you quote changed recently to http://www.bipm.org/en/publications/guides/vim.html .

I think I am probably more used to [a, b] to denote an interval (my upbringing in the UK) and hadn't appreciated that the French preference seems to be [a; b]  (page xiii in the VIM document, English language convention for interval uses [a, b] and page xv, French language convention for intervalle uses [a; b] ). I wonder if the use of a , is allowed as well?

Regards, Mark

Periodic Table of Isotopes for Educ. Community

Hi

In 2008 I sent the following e-mail to the then called online ‘orglist’:

“Hi organic chemistry list,
 
I was given this weblink recently. You can click on the elements and compounds for information (includes thermochemistry, NMR, lattice energies, biologcal, geology, physics roles etc and much more) . 

http://www.webelements.com/"

EOM

My question to the authors Holden & Tyler is: how much additional information do the authors provide in their table that may or may not be already contained in WebElements: the periodic table on the web at http://www.webelements.com/ ?

Note: Webelements gives information about isotopes of the elements (as well as a wealth of information incl. NMR, orbital properties … ). You just need to click on the box at the top of their page and then click on each element. They provide immediate and clear online information at a click of a button. They provide [take for example from their isotopes of fluorine] radioisotopes of fluorine, atomic masses, ½ lives, their nuclear spins, magnetic moments etc. Through their site you can also use Webelements to calculate an isotope pattern for an arbitrary chemical formula. They provide many references, the thermochemistry and the crystal structures of each element, lattice energies, biological/physical/chemical roles etc.

Thanks

Ling Huang, Sacramento City College

measuring uncertainty

Hi Tyler,

Thank you for your responses. I do have some more general and specific questions. Generally when we teach and in most text books a point estimate is used in calculations such as finding molar mass, number of moles, concentrations of solutions, number of atoms, number of molecules. So for example 12.01 is often used for carbon. This leads to point estimates. If we were to use lower and upper bounds, do we report lower and upper bounds of the molar mass etc? It would get very confusing. If we were to use a point estimate based upon intervals, do we use the mid-point of the interval? Or should we in fact look at the distribution of values within the range and based upon that distribution find the acceptable point? In your article you write:  ‘The standard atomic weight of an element should not be expressed as the average of a and b with an associated uncertainty of ± half of the range.’

Let’s examine carbon. In the article you calculate the lower bound by looking at the lowest measured C-13 abundance which at present reported is 12.009 662. Could this lowest value not change?  A certain number is then subtracted from this lowest value to find the lower bound. This lower number = the square root of (the square of ’the uncertainty of the delta measurement’ + ‘the square of the uncertainty in relating the carbon-delta scale to its atomic-weight scale’).

Then we take this number and take a little bit off it (truncation for the lower bound) ‘to ensure the atomic-weight interval encompasses the atomic-weight values of all normal materials’.

In your article for carbon ’the uncertainty of the delta measurement’ = 0.000003. Where does this number come from? Who chose and why 0.000003?

In your article for carbon ‘the uncertainty in relating the carbon-delta scale to its atomic-weight scale’ = 0.000027. Where does this number come from? Who chose and why 0.000027?

In the carbon case because you are squaring 0.000003 = 0.000000000009 and adding it to the square of a 1-decimal place significantly greater than number (then square root) this has no effect to the overall value of U[Ar(E)]p. How often does this happen? Does this happen with all of the 10 elements you mention on page 1? If it does happen then why are you considering the uncertainty of the delta measurement in the calculation? Actually why are the two uncertainties squared, added then square rooted to obtain an overall uncertainty?

I think there is a place for interval estimates, but when we teach there is a need for accurate point estimates in order not to clutter up or confuse the student. The teaching of isotopes then separately deals with the issue of various atomic weights etc. At the post graduate level these intervals and contentions of variability can and perhaps should be emphasized. So thank you for this interesting article and useful information.

Best wishes,

Ling

Ling Huang, Sacramento City College