Oganesson (Og), with atomic number 118, is not expected to be a gas at standard conditions, despite its position on the periodic table. This superheavy, synthetic element exists only fleetingly, making direct study extremely challenging. Its predicted properties are largely theoretical, differing significantly from its lighter counterparts due to complex atomic interactions.
What is Oganesson?
Oganesson (Og) is a synthetic, superheavy element with atomic number 118. It does not occur naturally on Earth and is instead created in specialized laboratories through nuclear fusion reactions. This process involves the collision of lighter atomic nuclei to form a heavier one. Oganesson is characterized by its extreme radioactivity and an incredibly short half-life, with its most common isotope, Oganesson-294, decaying in approximately 0.7 milliseconds. The fleeting existence of Oganesson-294 makes it exceptionally difficult to study directly, as only a handful of atoms have ever been successfully produced.
Oganesson’s Place Among Noble Gases
The question of whether Oganesson is a gas arises from its placement within Group 18 of the periodic table. This group is known as the noble gases, which include elements such as helium, neon, argon, krypton, xenon, and radon. These elements are characterized by their full outer electron shells, which makes them highly stable and unreactive. Under standard conditions, all the lighter noble gases exist as colorless, odorless, monatomic gases with very low boiling and melting points.
As the heaviest element in this group, Oganesson might intuitively be expected to share these gaseous properties and chemical inertness. Following periodic trends, elements generally become more metallic and less non-metallic down a group. This pattern could suggest that Oganesson would indeed behave like its noble gas predecessors. However, the extreme atomic mass and nuclear charge of Oganesson lead to significant deviations from these expected trends.
Why Oganesson is Not Expected to Be a Gas
Oganesson is not expected to be a gas due to unique atomic interactions known as “relativistic effects.” For elements with very high atomic numbers, electrons in the inner shells are accelerated to speeds approaching that of light. This extreme velocity causes electrons to gain significant mass and their orbits to contract, pulling them closer to the nucleus. This phenomenon, known as relativistic contraction, profoundly alters the electron cloud’s structure and behavior, especially for the outermost electrons that dictate chemical properties.
The strong relativistic effects in Oganesson cause a blurring or “smearing out” of its electron shells, particularly the valence electrons, making them behave more like a uniform electron gas. This altered electron configuration results in stronger interatomic forces than found in lighter noble gases. Theoretical calculations, which account for these relativistic effects, predict Oganesson will have a significantly higher melting point than what would be expected based on non-relativistic models. For instance, without considering relativity, Oganesson’s melting point would be around 220 K, suggesting a gaseous or liquid state at room temperature. However, with relativistic effects factored in, its melting point is predicted to be around 325 K (approximately 52 °C), indicating it would be a solid under standard conditions. This makes Oganesson behave more like a semiconductor or even a solid metal.
The Scientific Quest to Understand Oganesson
Direct experimental verification of Oganesson’s properties is nearly impossible. Its extreme instability and rarity necessitate a heavy reliance on theoretical models and sophisticated quantum mechanical calculations, specifically relativistic quantum chemistry, to predict its behavior. These calculations are crucial for understanding how its electrons behave under the immense nuclear charge.
Oganesson is synthesized in specialized facilities using particle accelerators. The process typically involves bombarding a target of Californium-249 atoms with a high-energy beam of Calcium-48 ions. This nuclear fusion reaction, represented as 249Cf + 48Ca → 294Og + 3n, creates the Oganesson nucleus along with three neutrons. Scientists continue to refine these methods and explore the possibility of creating more stable, heavier isotopes of Oganesson for more extensive chemical studies.