If you thought the information displayed in the periodic table was set in stone, think again. In a change that may see high school chemistry students shaking their heads in dismay, more information is to be added to the tables that appear in the fronts of textbooks.
The way the atomic weights of ten elements - including hydrogen, oxygen and nitrogen - are expressed is being modified to more accurately reflect their natural "isotopic" variation.
Since its introduction in 1869, the periodic table of the elements has accumulated many new entries. Only last year, copernicium was accepted into the table as element 112. The latest change is quite different, however.
Elements occur in different forms, known as isotopes. Carbon, for example, exists as three isotopes, each with different atomic weights (C-12, C-13, and C-14) and these are found in differing concentrations in different places. As a result, the periodic table currently contains atomic weights as an average of these different isotopic weights.
Now the International Union of Pure and Applied Chemists has decided to display the atomic weights of 10 elements as a range, rather than a single, average value.
Those elements affected are: hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium. Some elements, such as fluorine and gold, only exist in one form, so their weights are fixed.
While the new table might be more accurate, Ty Coplen, director of the USGS Reston Stable Isotope Laboratory in Virginia admits that "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."
Authors: James Brooks & Djuke Veldhuis | Source: New Scientist [December 16, 2010]