It is neat that we can still refine the
mensuration used for atomic weight on the periodic table for these ten elements. They all have an isotopic history that is
affected for external factors enough to introduce a lot of uncertainty.
In a couple of years you will be justified in
getting an up to date periodic table, though that has been common place enough
if one was in the habit of adding transuranic elements as they emerged from the
laboratories.
That this was needed was obvious for some
time. It is likely the methodology has
simply improved to the point that it is good enough to do the job for a long
time.
Atomic
weights of 10 elements on periodic table about to make an historic change
December
15, 2010
Michael
Wieser is a scientist from the University
of Calgary Calgary
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.
The
atomic weights of these 10 elements now will be expressed as intervals, having
upper and lower bounds, reflected to more accurately convey this variation in
atomic weight. The changes to be made to the Table of Standard Atomic Weights
have been published in Pure and Applied Chemistry and
a companion article in Chemistry International.
For
example, sulfur is commonly known to have a standard atomic weight of 32.065.
However, its actual atomic weight can be anywhere between 32.059 and 32.076,
depending on where the element is found. "In other words, knowing the
atomic weight can be used to decode the origins and the history of a particular
element in nature," says Wieser who co-authored the report.
Michael
Wieser, a professor at the University of Calgary, is contributing to changes to
the periodic table. He works with a thermal ionization mass spectrometer used
to measure the isotope abundance of an element. Credit: Riley Brandt/University
of Calgary
Elements
with only one stable isotope do not exhibit variations in their atomic weights.
For example, the standard atomic weights for fluorine, aluminum, sodium and
gold are constant, and their values are known to better than six decimal
places.
"Though
this change offers significant benefits in the understanding of chemistry, one
can imagine the challenge now to educators and students who will have to select
a single value out of an interval when doing chemistry calculations," says
Dr. Fabienne Meyers, associate director of IUPAC.
"We
hope that chemists and educators will take this challenge as a unique
opportunity to encourage the interest of young people in chemistry and generate
enthusiasm for the creative future of chemistry."
The University of Calgary University
of Calgary
This
fundamental change in the presentation of the atomic weights is based upon work
between 1985 and 2010 supported by IUPAC, the University of Calgary
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