The identity of any chemical element is determined by the number of protons in its atomic nucleus. This count, known as the atomic number (Z), dictates the element’s position on the periodic table and its chemical properties. The search for new elements creates increasingly massive and unstable atoms that exist only for fleeting moments. This pursuit of superheavy elements has culminated in the creation of the heaviest element known today.
The Significance of Atomic Number 118
Oganesson has 118 protons in its nucleus, giving it an atomic number (Z) of 118. This proton count places it at the end of the seventh period on the periodic table. The element is officially designated with the chemical symbol Og.
Before its official assignment, Oganesson was temporarily known as ununoctium, derived from the Latin terms for its atomic number. The formal name was approved by the International Union of Pure and Applied Chemistry (IUPAC) in 2016, honoring Russian nuclear physicist Yuri Oganessian. This naming acknowledges Oganessian’s pioneering contributions to the discovery of superheavy elements.
Defining Oganesson
Oganesson is classified as a superheavy, synthetic element, distinguishing it from the 94 elements found naturally on Earth. It is the only synthetic member of Group 18, which consists of the noble gases. Although its placement suggests non-reactive properties, its immense size complicates this expectation.
Oganesson provides evidence for the theoretical “Island of Stability,” a region where specific combinations of protons and neutrons are predicted to yield longer-lived nuclei. Oganesson-294 is extremely short-lived, with a half-life of less than one millisecond, but its measured decay time exceeds initial predictions. Scientists theorize that isotopes with around 184 neutrons might be significantly more stable, residing closer to the center of this predicted island.
The confirmation of Oganesson confirms that the strong nuclear force can hold together a nucleus with a high number of positive charges. Oganesson represents the current limit of elements synthesized by human effort.
Synthesizing Superheavy Elements
Oganesson cannot be found in nature because its nuclei are too unstable to persist, meaning every atom must be created in a laboratory. Creating an element with 118 protons requires a high-energy nuclear reaction performed in a particle accelerator, such as the cyclotron at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. The synthesis involves nuclear fusion where two lighter nuclei are smashed together.
Scientists created Oganesson by bombarding Californium-249 (98 protons) with a beam of Calcium-48 ions (20 protons). The sum of these protons (98 + 20) equals the 118 protons required for Oganesson. This process is highly inefficient, requiring the irradiation of the Californium target over hundreds of hours.
The fusion event forming Oganesson-294 is accompanied by the expulsion of three free neutrons. Scientists confirmed the element’s brief existence by tracking its specific radioactive decay chain, not by direct observation.
Oganesson-294 immediately undergoes alpha decay, losing two protons and two neutrons to become Livermorium-290, which then decays further. Detecting this unique sequence of decay events verifies the element’s synthesis.
How Relativity Changes Oganesson’s Chemistry
The high number of protons in Oganesson’s nucleus creates an immense positive charge that influences the surrounding electrons. This strong attraction causes inner electrons to accelerate to near the speed of light, introducing significant relativistic effects that alter the element’s chemistry. These effects fundamentally change the electron orbital structure, causing shells to contract and split in ways that defy classical chemistry predictions.
The traditional expectation for a Group 18 element is that it would be an inert gas. However, Oganesson is predicted to deviate dramatically. Theoretical calculations suggest relativistic effects enhance the attraction between Oganesson atoms, giving it a predicted melting point of about 325 Kelvin. This means it would likely be a solid under standard conditions, contrasting with the gaseous state of all its lighter noble gas counterparts.
The relativistic modification of its electron configuration suggests Oganesson may be more chemically reactive than any other noble gas. It is predicted to have a higher dipole polarizability and may exhibit variable oxidation states, such as +2 and +4, behaviors not seen in lighter noble gases.