The periodic table has expanded significantly in the last century, moving far beyond naturally occurring elements. This modern expansion involves creating entirely new elements that do not exist in bulk quantities on Earth. These synthesized atoms challenge the limits of nuclear structure and stability. Their nature is fundamentally different from historically discovered elements because their existence is fleeting, requiring immense energy and specialized technology for creation. Understanding these additions provides deep insights into the forces that hold the atomic nucleus together.
Defining the Newest Elements
The newest elements are formally defined as transuranic elements, possessing an atomic number greater than 92 (the proton count of uranium). Except for trace amounts of neptunium and plutonium found in uranium ore, all elements beyond uranium must be created artificially in a laboratory setting. This synthetic nature is their defining characteristic because their extremely short half-lives ensure any primordial atoms have long since decayed. Consequently, the study of these elements is limited to a microscopic scale, as they are often produced one atom at a time.
Scientists cannot collect these superheavy elements into a visible sample or weigh them on a scale. Instead, they are identified solely through the unique signatures of their radioactive decay chains. The scarcity and rapid decay necessitate highly sensitive detection equipment. This equipment records the exact sequence of particles emitted from a single nucleus, confirming the element’s identity and providing data on its nuclear properties.
How Superheavy Elements Are Synthesized
Superheavy elements are created through nuclear fusion reactions conducted within particle accelerators. This process involves bombarding a heavy target nucleus with a beam of lighter projectile ions at high speeds. The goal is to fuse the two nuclei into a single, heavier, and highly unstable compound nucleus. The efficiency of this fusion is incredibly low, often requiring billions of collisions to produce a single new atom.
Two primary approaches are used to achieve this fusion, often referred to as “cold” and “hot” fusion. The cold fusion method typically involves bombarding a heavy, stable target like lead or bismuth with a medium-weight projectile, resulting in a compound nucleus with a lower internal excitation energy. Facilities like the GSI Helmholtz Centre in Germany successfully used this method to discover elements up to copernicium (element 112). These reactions tend to stabilize the new nucleus by releasing one or two neutrons.
The hot fusion method, used at the Joint Institute for Nuclear Research in Dubna, Russia, uses a more neutron-rich projectile, specifically calcium-48 (Ca-48), to bombard actinide targets such as curium or californium. This creates a compound nucleus with significantly higher excitation energy, which then stabilizes by “boiling off” three or four neutrons. The use of the neutron-rich Ca-48 beam is advantageous because it pushes the newly formed nucleus closer to the theoretically stable region of the nuclear chart.
Characteristics of Extreme Instability
The defining characteristic of the newest elements is their profound nuclear instability, quantified by their extremely short half-lives. For the heaviest synthesized elements, this half-life often ranges from milliseconds to mere seconds. Some isotopes of oganesson (element 118) decay in less than a thousandth of a second. This rapid decay explains why these elements cannot be observed in nature.
The primary ways these unstable nuclei decay are through alpha decay and spontaneous fission. Alpha decay involves the emission of an alpha particle, which is the nucleus of a helium atom, reducing the atomic number by two and starting a decay chain that eventually leads to a known, lighter element. Spontaneous fission, on the other hand, is the immediate splitting of the nucleus into two or more smaller nuclei, often with the release of several neutrons. The specific decay mode observed helps physicists map the nuclear structure of the new element.
A major theoretical concept driving current research is the “Island of Stability,” a predicted region where superheavy elements might exhibit significantly longer half-lives than their immediate neighbors. This theoretical increase in stability is attributed to “magic numbers” of protons and neutrons that create closed nuclear shells, similar to the electron shells that determine chemical stability. While most superheavy elements decay rapidly, the hope is that isotopes with certain neutron counts, possibly near the magic number of 184, will have half-lives potentially measured in minutes, days, or even longer. This extended lifespan would allow chemists to perform more extensive experiments to determine the new element’s chemical properties.
Official Discovery and Naming Conventions
The process of officially adding a new element to the periodic table is overseen by the joint working group of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP). Before recognition, the discovery claim must be independently confirmed by a second laboratory to ensure validity and reproducibility. This verification process can take years, especially when multiple research teams submit competing claims for the same element.
Once the joint working group confirms the discovery, the collaborating scientists are invited to propose a permanent name and a one- or two-letter symbol. In the interim period, before the name is officially approved, the element is referred to by its atomic number or a provisional systematic name, such as ununseptium for element 117. The final names often follow a tradition of honoring a mythological concept, a geographical region, a mineral, or a scientist. After a public review period, the IUPAC Council grants the final ratification, formally cementing the element’s place on the periodic table.