Tennessine (Ts), element 117, is a synthetic, superheavy element produced only in minute quantities within particle accelerators. With an atomic number of 117, Ts is profoundly unstable; the most stable isotope, Tennessine-294, has a half-life of only about 80 milliseconds before decaying into another element. Studying the chemical properties of such an ephemeral substance is impossible through direct experimentation. Scientists must rely on advanced theoretical models, which suggest that the fundamental rules of chemistry governing its outermost electrons are dramatically altered for Tennessine.
What Are Valence Electrons?
Valence electrons are the electrons located in the outermost shell of an atom, determining an element’s chemical reactivity and bonding behavior. Atoms are structured with electrons arranged in shells around the central nucleus, but only those on the periphery participate in forming chemical bonds. The number of these outer electrons dictates whether an atom will readily share, gain, or lose electrons. A fundamental concept in chemistry is the tendency for atoms to achieve a stable configuration, often by possessing eight electrons in their valence shell, a principle known as the octet rule.
Determining Tennessine’s Standard Electron Count
Based purely on its position in the periodic table (Group 17, Period 7), Tennessine is predicted to have seven valence electrons, placing it as the heaviest member of the halogen family. The standard theoretical electron configuration for Tennessine is \([Rn]5f^{14}6d^{10}7s^27p^5\). In this configuration, the outermost (seventh) shell contains two electrons in the \(7s\) subshell and five electrons in the \(7p\) subshell, summing to seven outer electrons.
Tennessine’s Place on the Periodic Table
The standard count of seven valence electrons places Tennessine in Group 17, the halogen family, alongside Fluorine, Chlorine, Bromine, Iodine, and Astatine. This classification typically predicts high chemical reactivity, as the atom would only need to acquire one additional electron to complete its octet. By gaining a single electron, Tennessine would be expected to form a stable, negatively charged ion, \(Ts^-\). Based on periodic trends, Tennessine is expected to have the largest atomic radius and the lowest first ionization energy and electron affinity within the halogen group. However, the immense number of protons in its nucleus fundamentally changes the behavior of its electrons, causing its chemistry to diverge from the expected halogen pattern.
How Relativistic Effects Change the Prediction
The immense positive charge of Tennessine’s nucleus causes its innermost electrons to accelerate to near the speed of light. This relativistic speed dramatically increases the mass of the electrons, altering the shape and energy of their orbitals. The classical rules of chemistry break down, necessitating the use of relativistic quantum mechanics for accurate predictions. One primary consequence is the direct relativistic effect, which causes the \(s\) and \(p_{1/2}\) electron orbitals to contract toward the nucleus.
Because the \(7s\) electrons are pulled closer and stabilized in energy, they become much less available for chemical bonding. This effect is so pronounced that theoretical models hypothesize the \(7s\) electrons may become chemically inert, effectively reducing the number of chemically available valence electrons from seven to five. A second effect, the indirect relativistic effect, destabilizes and expands the \(7p_{3/2}\) subshell, making those electrons less tightly bound. Due to the combination of a stabilized \(7s\) subshell and a destabilized \(7p_{3/2}\) subshell, Tennessine is predicted to favor positive oxidation states like \(+1\) or \(+3\) and may even exhibit metallic properties, rather than easily forming a \(-1\) ion like a standard halogen.