Eldritch
01-12-2011, 06:01 PM
Atomic Weights of Ten Chemical Elements About to Change
For the first time in history, a change will be made to the atomic weights of some elements listed on the Table of Standard Atomic Weights of the chemical elements found in the inside covers of chemistry textbooks worldwide.
The International Union of Pure and Applied Chemistry’s (IUPAC) Commission on Isotopic Abundances and Atomic Weights is publishing a new table that will express atomic weights of ten elements as intervals, rather than as single standard values. The new table is the result of cooperative research supported by the U.S. Geological Survey, IUPAC, and other contributing Commission members and institutions.
Standard atomic weights commonly are thought of as constants of nature, despite the fact that atomic weights of many common chemical elements show variations as a result of physical, chemical and biological processes.
...
The standard atomic weights for hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium previously were expressed as central values with uncertainties that reflected natural atomic-weight variations.
The weights of these elements now will be expressed as intervals to more accurately convey this variation in atomic weight. For example, boron is commonly known to have a standard atomic weight of 10.811. However, its actual atomic weight can be anywhere between 10.806 and 10.821, depending on where the element is found.
The atomic weight of an element depends upon how many stable isotopes it has and the relative amount of each stable isotope. Isotopes are atoms of the same element that have different masses. Variations in atomic weight occur when an element has two or more naturally occurring stable isotopes that vary in abundance.
Link. (http://www.eoearth.org/article/Atomic_Weights_of_Ten_Chemical_Elements_About_to_C hange?topic=49557)
For the first time in history, a change will be made to the atomic weights of some elements listed on the Table of Standard Atomic Weights of the chemical elements found in the inside covers of chemistry textbooks worldwide.
The International Union of Pure and Applied Chemistry’s (IUPAC) Commission on Isotopic Abundances and Atomic Weights is publishing a new table that will express atomic weights of ten elements as intervals, rather than as single standard values. The new table is the result of cooperative research supported by the U.S. Geological Survey, IUPAC, and other contributing Commission members and institutions.
Standard atomic weights commonly are thought of as constants of nature, despite the fact that atomic weights of many common chemical elements show variations as a result of physical, chemical and biological processes.
...
The standard atomic weights for hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium previously were expressed as central values with uncertainties that reflected natural atomic-weight variations.
The weights of these elements now will be expressed as intervals to more accurately convey this variation in atomic weight. For example, boron is commonly known to have a standard atomic weight of 10.811. However, its actual atomic weight can be anywhere between 10.806 and 10.821, depending on where the element is found.
The atomic weight of an element depends upon how many stable isotopes it has and the relative amount of each stable isotope. Isotopes are atoms of the same element that have different masses. Variations in atomic weight occur when an element has two or more naturally occurring stable isotopes that vary in abundance.
Link. (http://www.eoearth.org/article/Atomic_Weights_of_Ten_Chemical_Elements_About_to_C hange?topic=49557)