Oganesson (Og), element 118, holds the distinction of being the heaviest element currently known to science, a synthetic achievement that completes the seventh period of the periodic table. Its creation requires bombarding californium-249 atoms with calcium-48 ions in a particle accelerator, yielding only a handful of atoms that decay in a fraction of a millisecond. This extreme instability and scarcity mean that its properties, including the behavior of its outermost electrons, cannot be directly measured. The question of how many electrons Oganesson has available for bonding must instead be answered through advanced theoretical predictions.
Fundamental Chemistry: Defining Valence Electrons
Valence electrons are the electrons that occupy the outermost shell of an atom. They are the furthest from the nucleus and are the primary participants in chemical reactions and bond formation. The number of these outer-shell electrons dictates an element’s chemical properties, such as its reactivity and the number of bonds it can typically form.
In main-group elements, the total count of valence electrons is easily determined by the element’s group number on the periodic table. Atoms strive to achieve a full outer shell, a stable configuration usually consisting of eight electrons, known as the octet rule. Elements with a full outer shell are chemically inert.
Oganesson’s Position on the Periodic Table
Oganesson is positioned in Group 18 of the periodic table, which is also its seventh and final period. Group 18 is traditionally known as the noble gases, including elements like neon, argon, and xenon, which are characterized by their complete valence electron shells. Based on this standard periodic arrangement, Oganesson is predicted to be the heaviest member of this group, sometimes referred to as eka-radon.
Following the conventional rules for main-group elements, an element in Group 18 is expected to possess eight valence electrons. This placement suggests Oganesson should be an inert gas with a zero-valence state, meaning it would not readily form chemical bonds. However, Oganesson is a synthetic, radioactive element with a half-life of less than a millisecond, which makes experimental confirmation of its noble gas behavior impossible. Its superheavy nature introduces complex physics that challenge the simple predictions based on its location in the table.
The Specific Count of Oganesson’s Valence Electrons
The theoretical electron configuration for a neutral Oganesson atom is calculated to be \([Rn]5f^{14}6d^{10}7s^27p^6\). The \(7s\) subshell holds two electrons, and the \(7p\) subshell holds six electrons, totaling eight valence electrons.
This count of eight electrons confirms the expectation derived from its position in Group 18, placing Oganesson theoretically in the category of elements with a stable, closed-shell configuration. The \(7s^27p^6\) arrangement suggests a zero-valence state and chemical inertness, mirroring the behavior of the lighter noble gases. However, the physical reality of Oganesson’s chemistry is far more complex than this simple count suggests due to the extreme conditions within its atom.
The Relativistic Effects Complicating the Count
The high atomic number of Oganesson (118 protons) creates an enormous positive charge in the nucleus. This intense charge causes the inner-shell electrons to accelerate to speeds approaching the speed of light. Such high speeds introduce relativistic effects, which significantly alter the behavior of Oganesson’s electrons compared to those in lighter elements. This phenomenon fundamentally changes the electronic structure, making the simple count of eight valence electrons chemically ambiguous.
One major consequence is the relativistic mass increase of the electrons, which results in the contraction and stabilization of the \(s\) and \(p_{1/2}\) orbitals. The \(7s\) electrons are pulled closer to the nucleus, making them much harder to remove or share in a bond. Conversely, the \(7p\) orbital splits into \(7p_{1/2}\) and \(7p_{3/2}\) subshells due to strong spin-orbit coupling, a relativistic interaction between the electron’s spin and its orbital motion.
This splitting of the \(7p\) energy levels is so pronounced that the traditional separation between the \(7s\) and \(7p\) subshells effectively disappears. The electrons are no longer neatly organized into distinct shells and subshells, but are instead “smeared out” into a more uniform distribution, sometimes described as an electron gas. This delocalization suggests that the concept of a clearly defined valence shell, which underpins the count of eight, may break down entirely for Oganesson.
These complex relativistic interactions predict that Oganesson will not behave like a typical noble gas. The tightly bound \(7s\) electrons and the split \(7p\) subshells mean that Oganesson’s ionization energy is predicted to be relatively low. This suggests it might actually be more reactive than its lighter congener, Radon.
Theoretical calculations even predict that Oganesson could form stable compounds and exhibit multiple positive oxidation states, such as \(+2\) and \(+4\). This behavior contrasts sharply with the inert gases above it.
Models suggest that Oganesson may be a solid at room temperature, a contrast to all other gaseous noble gases, and may even behave as a semiconductor. This is due to a predicted narrow band gap between the filled valence orbitals and the empty conduction orbitals, a direct result of the relativistic changes to the electronic structure.