Tennessine (Ts), element 117, is a recently synthesized superheavy element located in Group 17 of the periodic table, directly below astatine. Its extreme mass causes its properties to deviate significantly from the periodic trends established by its lighter counterparts. Since only a few atoms of tennessine have been created, and they decay in milliseconds, its classification relies on theoretical predictions and computational chemistry.
How Elements Are Classified
Elements are broadly categorized based on a set of characteristic physical and chemical properties. Metals are typically solid at room temperature, possess a shiny luster, and are excellent conductors of both heat and electricity. They are also known for being malleable and ductile. Chemically, metals tend to lose electrons easily, resulting in a low ionization energy.
Nonmetals, located generally on the right side of the periodic table, exhibit properties opposite to those of metals. They are poor conductors of heat and electricity, lack metallic luster, and are often brittle when solid. Nonmetals prefer to gain electrons in chemical reactions, which means they have high ionization energies.
Metalloids, sometimes called semimetals, occupy a zigzag line separating metals and nonmetals on the table and display properties intermediate between the two categories. These elements can have a metallic appearance but are often brittle, and their most distinguishing feature is their ability to act as semiconductors. This means they conduct electricity better than nonmetals but not as well as metals.
The Predicted Properties of Tennessine
Based purely on its position in Group 17, periodic trends suggest that tennessine should be the heaviest halogen, exhibiting nonmetallic or metalloid characteristics similar to astatine. However, theoretical calculations indicate that tennessine’s properties will be dramatically different from the volatile nonmetals, such as chlorine or bromine, that precede it in the group.
Tennessine is predicted to be a solid at room temperature and potentially have a dark, metallic appearance. Its ionization potential, the energy required to remove an electron, is calculated to be much lower than expected for a halogen, suggesting a greater tendency to lose electrons. This low ionization energy is a characteristic sign of metallic behavior.
In terms of chemical reactivity, the lighter halogens are known to favor a -1 oxidation state by gaining one electron to complete their outer shell. Tennessine, in contrast, is predicted to have a much more stable +1 oxidation state, and even a +3 state could be as important as the -1 state. This tendency to easily lose electrons and form positive ions is a strong indicator of metallic or metal-like character.
Why Relativistic Effects Change Element 117
The fundamental reason tennessine defies simple periodic trends lies in a phenomenon known as relativistic effects. For elements with an atomic number as high as 117, the massive positive charge of the nucleus accelerates the innermost electrons to speeds approaching the speed of light. According to Einstein’s theory of relativity, this extreme velocity causes the mass of these electrons to increase significantly.
This increase in electron mass profoundly impacts the shape and energy of the electron orbitals. The s and p orbitals, which are close to the nucleus, contract radially toward the center. This contraction stabilizes the electrons in these orbitals, making them much harder to remove.
Conversely, the contraction of these inner orbitals effectively shields the outer d and f orbitals, causing them to expand and become destabilized. In tennessine, this results in the valence electrons behaving in a less tightly bound manner than expected for a halogen. This drives the element toward metallic behavior by significantly reducing its predicted nonmetallic character.
The Current Classification Consensus
The consensus leans strongly against classifying tennessine as a traditional nonmetal like the lighter halogens. The predicted metallic luster, lower-than-expected ionization energy, and preference for forming positive oxidation states all point away from typical halogen properties.
While some early predictions suggested it might be a metalloid, the magnitude of the relativistic effects is so great that tennessine is now widely predicted to be a metal-like element. The term “Post-Transition Metal” is often used to describe its likely behavior, meaning it would possess significant metallic character.
The element’s extremely short half-life of about 80 milliseconds means a definitive experimental classification remains impossible. However, theoretical models indicate that tennessine will behave more like a metal than a metalloid or a nonmetal.