The periodic table has expanded recently with the creation of synthetic, superheavy elements. These elements do not occur naturally and are forged in specialized laboratories. Their existence completes the seventh row of the table, offering physicists a glimpse into the behavior of matter at its limit. Creating these new atomic species requires immense energy and cutting-edge technology, pushing the boundaries of nuclear science.
Element 118: Identification and Basic Characteristics
The most recently discovered element officially recognized is Oganesson (Og), designated by the atomic number 118. This synthetic element completes the seventh period of the periodic table and is classified as a transuranium element, meaning its atomic number is greater than that of uranium (92).
Oganesson is positioned in Group 18, the column known for noble gases. Theoretical models suggest Oganesson may not behave like a typical noble gas due to relativistic effects altering its properties. The element is extremely unstable; its most stable isotope, Oganesson-294, has a half-life of approximately 0.7 milliseconds. This rapid decay limits the ability to experimentally study its chemical and physical characteristics.
Synthesizing Superheavy Elements in the Lab
The creation of superheavy elements relies on “hot fusion,” which requires a powerful particle accelerator. This process involves accelerating a beam of lighter, positively charged nuclei and smashing them into a target made of a heavier element. For Oganesson-294, scientists in Dubna, Russia, used a beam of Calcium-48 ions directed at a target of Californium-249.
Calcium-48 was chosen because its neutron-rich nucleus helps stabilize the resulting superheavy nucleus. The calcium ions were accelerated to overcome the strong repulsive force between the positive charges and briefly fuse. This collision must be precisely tuned to ensure the nuclei fuse without immediately breaking apart, forming a compound nucleus. Successful fusion is exceedingly rare, often creating only a few atoms before the target material is depleted.
The resulting compound nucleus of Oganesson is highly excited and immediately sheds excess energy by evaporating neutrons, typically three, to reach a more stable state. Scientists use magnetic separators to filter the desired atoms from the stream of unreacted particles and byproducts. The Oganesson atom is detected indirectly by observing the characteristic sequence of alpha particles it emits as it decays through a chain of lighter elements. Hot fusion, using neutron-rich materials, has been the most successful method for synthesizing the heaviest elements.
The Official Process for Naming and Validation
The journey to a permanent place on the periodic table is overseen by international scientific bodies. The discovery claim is first reviewed by the Joint Working Party (JWP), a committee composed of members from the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP). This group rigorously examines the experimental data to determine if the evidence is sufficient and reliable.
A discovery is confirmed only when independent laboratories have successfully reproduced the results, observing the same identifying decay chains. Before official recognition, the element is given a temporary systematic name based on its atomic number, such as “ununoctium” for Element 118. Once the JWP verifies the discovery, the claiming team proposes a permanent name and symbol to the IUPAC Inorganic Chemistry Division.
IUPAC guidelines allow new elements to be named after a mythological concept, a mineral, a place, a property, or a scientist. The discoverers of Element 118 proposed Oganesson, honoring Russian nuclear physicist Yuri Oganessian. The proposed name undergoes a public review before the IUPAC Council grants final ratification, a process that can take several years. Oganesson was formally approved in November 2016, and its “-on” ending maintains consistency with other Group 18 noble gases.
The Future: Searching for the Island of Stability
The synthesis of Element 118 has prompted physicists to focus on the search for elements 119 and 120, which will begin the eighth row. This pursuit is driven by the theoretical “Island of Stability.” Nuclear models predict that a specific combination of protons and neutrons, known as “magic numbers,” could result in nuclei with significantly enhanced stability.
While current superheavy elements decay in milliseconds, elements on the theoretical island are predicted to have half-lives measured in minutes, hours, or longer. The center of this island is believed to reside around elements with 114 to 126 protons and 184 neutrons. Reaching this region requires more powerful accelerators and increasingly neutron-rich projectiles and targets, as the supply of necessary actinide targets is limited.
Experiments are underway globally to synthesize elements 119 and 120, for example, by bombarding curium-248 with a vanadium-51 beam. The challenge is immense because the probability of successful fusion decreases dramatically with each heavier element. Proving the existence of the Island of Stability would provide profound insights into the fundamental forces governing the atomic nucleus.