Author: David Mertz
Editors: Tricia Garay, Irene Park
Ever since an interactive display was built in my high school chemistry lab (one of only six such installations in the world), I’ve found the periodic table of elements to be a fascinating fixture of science. I remember watching the scientists prepare little displays for each individual element, including the metal gallium which they let me hold in my hand. It was different than most of the metals familiar to us. With a melting temperature just below 30 degrees Celsius (86 degrees Fahrenheit), the metallic cube began to melt right on my palm.
The periodic table of elements is fascinating because it maps the relationships between a wide variety of substances. Developed by chemists, the table categorizes each element based on the chemical and physical properties of its atoms. Electrons, the subatomic particles that impart atoms with their chemical characteristics, circle the central nucleus in distinct orbits or shells, similar to how planets orbit a star, if multiple planets could travel in the same orbit. The row, or period, that an element occupies in the table indicates the number of shells that its electrons inhabit. The column, or family, is assigned based on the number of electrons in the outer shell alone. These valence electrons dictate the element’s tendency to chemically react with other atoms and molecules.
But I always wondered about the squares in the bottom-right corner of the periodic table—with their strange names and three-letter symbols. Ununtrium. Ununpentium. Ununseptium. Ununoctium. Bizarre Latin placeholder words which literally translate to their atomic numbers: 113, 115, 117, and 118. In our interactive table, the display for each of those elements was represented by a generic silhouette with a question mark, indicating where mankind’s knowledge of chemistry came up short.
Just this summer, those last few spaces have been filled in. The existence of these elements have been confirmed, and they have been given proper names, completely filling the seven rows–or periods–of the periodic table. On June 8th, 2016 the International Union of Pure and Applied Chemistry (IUPAC) revealed the chosen names for the last four unnamed elements: nihonium (113), moscovium (115), tennessine (117), and oganesson (118).
Because the honor of naming the element is traditionally bestowed upon the discoverer, these elements were named after the locations, people, or labs where they were discovered, immortalizing those contributors in the annals of chemistry research. Nihonium was named after the place of its confirmed discovery in 2012: Nihon, is the Japanese word for Japan. Similarly, moscovium was named in honor of the city of Moscow, near where it was discovered. Tennessine joins californium as the second element to be named after a state in the United States; the Oak Ridge National Laboratory in Tennessee was credited, in part, for its discovery. Oganesson is the only new inductee to be named after a living person, Yuri Oganession, an 83-year old Russian scientist at the same institute that discovered moscovium.
Looking further back on the table, plutonium (94), on the seventh row, is the heaviest element known to exist in nature. Over millions of years, it slowly undergoes radioactive decay until reaching its most stable form. Every element heavier than plutonium has needed to be synthesized in a laboratory in order to be “discovered,” each being more radioactive and unstable than plutonium. The least stable elements last for fractions of a second before decaying. All sit on the seventh row.
As new elements have been discovered and characterized throughout history, the periodic table has had to be rearranged to reflect its changing categorization. For aesthetic reasons and for their unique arrangement of electrons, two rows of elements—the actinides (elements from 57 to 70) and lanthanides (elements from 89 to 102)—are detached from the rest of the table. The current arrangement of the periodic table has held mainstream acceptance for decades since.
The contemporary periodic table has also helped scientists to predict the properties of chemical elements yet to be discovered—including these four newest additions. In fact, a primary reason for synthesizing new heavy elements has been to test those predictions to see whether, during their short existence, they share the same properties of the elements in the rows above them. The table predicts that tennessine will fall in with the halogens like chlorine, bromine, and iodine. Oganesson is now the heaviest member of Group 18, the noble gasses, which include neon and argon.
Maybe now is the right time to leave the table as it is – an example of how nature, seemingly chaotic, remains ordered at its most fundamental level.
So far, most of the larger synthetic elements have not shown any potential for commercial value given their minuscule half-lives (the time it takes for half of a sample to radioactively decay). The bottom-right corner of the table has been filled in, but the quest to synthesize new, even heavier elements continues. These efforts are mainly driven by a desire to push the boundary of knowledge and disprove existing models again and again. Already, the heaviest elements have shown discrepancies in their behavior compared to their lighter counterparts in the same family. Few things would be more amazing in chemistry than discovering that the next-heaviest element, number 119, has chemical properties nothing like those of the alkali metals in the left-most column above it.
Perhaps then the table would need to be modified, inspiring a new generation of chemistry questions and experiments about the unique behavior of heavy atoms. With each new element discovered after oganesson, the rationale behind the current table’s format will be tested. The motivation to find heavier and heavier elements might only dissipate if the next-heaviest elements actually hold to their predicted properties. If they do, the global body of chemistry researchers may quietly groan.
About the author
David is a biomedical engineering doctoral student and lifelong Michigan resident. Having recently earned bachelor’s and master’s degrees at the University, he now works in the laboratory of Shuichi Takayama, developing better in vitro organ-on-a-chip and human-on-a-chip models for drug screening and disease study. In addition to his research and writing for the MiSciWriters blog, David also writes science-focused opinion columns for the Michigan Daily and enjoys training with the Ann Arbor Rowing Club. You can follow him on Twitter (@davrmertz) and connect on LinkedIn (linkedin.com/in/drmertz).
Read more from David here.
Phosphorous: By commons:User:Pumbaa (original work by commons:User:Greg Robson) – http://commons.wikimedia.org/wiki/Category:Electron_shell_diagrams (corresponding labeled version), CC BY-SA 2.0 uk, https://commons.wikimedia.org/w/index.php?curid=22301817
Periodic table: By Sandbh – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45579529