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Where Does the Periodic Table End?

iStockphoto/agsandrew

iStockphoto/agsandrew

By Colin A. Scholes

The United Nations has declared 2019 as the International Year of the Periodic Table of the Chemical Elements to highlight its first publication 150 years ago. Since then, new elements have been added to the table. Is there a final element, or are ever-increasing atomic numbers possible?

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The periodic table could be considered to end at the largest stable element, lead (atomic number 82). All elements with higher atomic numbers have unstable nuclei, because the assembled protons become too large for the strong nuclear force to hold together. Hence, all those elements with atomic numbers greater than that of lead will eventually undergo radioactive decay to reduce their atomic number to 82 or less; as such, these elements can be considered transients.

However, many of these higher elements have half-lives comparable to the age of the universe. For instance, bismuth (atomic number 83) was considered stable, until in 2003 it was found to be very slightly unstable with a half-life of 1.9 ×1019 years. This half-life is more than a billion times longer than the current age of the universe, and so bismuth as an element may outlast the universe.

Similarly, the longest-lived isotope of thorium (atomic number 90) has a half-life of 1.4 × 1010 years and will remain with us for billions of years to come. The longest-lived isotope of uranium (atomic number 92) has a half-life of 4.5 × 109 years, followed by plutonium (94, with a half-life of 7.9 × 107 years) and curium (96), whose most stable isotope has a half-life of 1.6 × 107 years.

As atomic number increases after curium, the half-lives of...

The full text of this article can be purchased from Informit.