Hot on the heels of recent news that four new elements have been accepted into the periodic table, Ivan Semeniuk has produced an excellent guide to the periodic table's history and the new elements for the Globe and Mail.
The periodic table is essentially a depiction of all the different types of atoms (elements) that make up the universe around us, as well as a few man-made ones, listed in order of increasing mass (basically, the number of protons they contain).
When the universe began, with the Big Bang, the energy released created all the hydrogen (the simplest and lightest all the elements) in the universe, plus a much smaller amount of helium (the second-lightest element), and tiny trace amounts of a few others. The other heavier elements were created in the nuclear reactions of the first stars and in their cataclysmic deaths as supernovas.
In the 1860s, when only 53 different elements were known, Russian chemist Dmitri Mendeleev realized that they could be arranged in a table of increasing atomic mass, and that this arrangement also grouped together elements with similar chemical properties. For example, the alkaline metals are all in the first column of the table, the noble gases in the 18th and final column, etc. Because of the recurring similarities in these groups, he called his chart the periodic table. At that time, there were still gaps in the table, and Mendeleev confidently predicted the subsequent discovery of new elements with particular properties, predictions which started to come true within just a few years.
As our chemical knowledge and scientific techniques improved over time, more and more elements were added to the table. Eventually, elements were created in laboratories (by smashing together atomic nuclei at extremely high speeds) that do not exist in nature, elements that are heavier and more unstable than the heaviest naturally-occurring element, uranium (atomic number 92). The first of these were neptunium and plutonium, which were discovered in the 1940s. The race to synthesize new elements has become highly competitive, even though these new elements are generally very unstable and short-lived, and do not offer many practical benefits.
Recently, the International Union of Pure and Applied Chemistry, the body that oversees the periodic table and the naming of elements, has accepted the discovery of four new elements for inclusion in the table, neatly finishing off Row 7. These elements, the first to be accepted into the table since 2011, do not have names yet, but are just known by the names unumtrium (113), unumpentium (115), unumseptium (117) and unumoctium (118). All four only last for milliseconds, and disintegrate and decay almost as soon as they are created. In a sharp break with the generally very Eurocentric periodic table, the discovery of element 113 is credited to a Japanese team, and the other three to a US-Russian collaboration, which may make naming them somewhat contentious. The teams have five months to submit names for the new elements to the IUPAC, names which can only refer to mythological concepts or characters, minerals, places or geographic regions, chemical properties of the element, or the names of scientists.
With the completion of Row 7 and no obvious gaps, the periodic table has probably never looked so neat and tidy, but efforts to create elements beyond 118 are ongoing (no claims have been made thus far). Helping to drive this effort is the tantalizing possibility, first theorized in the 1960s, that there may potentially be a group of very heavy but long-lived, elements that exists like a stable island in the midst of a sea of instability. Such stable, heavy elements could have important scientific applications, but for now at least they remain pure conjecture.
No comments:
Post a Comment