The search for elements beyond the 118 currently known drives modern scientific exploration, pushing the boundaries of our understanding of matter. An element is fundamentally defined by the number of protons residing within the nucleus of its atoms. This unique proton count, known as the atomic number, dictates an element’s identity. The ongoing quest involves not only searching for new naturally occurring elements but also creating entirely new forms of matter that have never before existed.
The Current Periodic Table
The periodic table organizes all known chemical elements, systematically arranging them by their atomic number. Each position on the table represents an element with a distinct number of protons, from hydrogen with one proton to oganesson with 118 protons. This arrangement also groups elements with similar chemical properties, reflecting recurring patterns in their behavior. While many elements exist naturally on Earth, some of the heaviest elements are not found in nature and can only be produced through synthetic means in laboratories. These laboratory-created elements extend the periodic table beyond what was once thought possible, showcasing the dynamic nature of scientific discovery.
Creating New Elements in the Lab
Scientists synthesize new, superheavy elements by overcoming the natural repulsion between positively charged atomic nuclei. This process, a form of nuclear fusion, involves accelerating lighter nuclei to extremely high speeds. These accelerated “projectile” nuclei are then directed to collide with a “target” nucleus, with the aim of fusing them into a single, heavier nucleus. Such experiments are conducted in specialized facilities like particle accelerators, where precise control over the collision energy is maintained.
The conditions required for these fusion reactions are extreme, making the creation of new elements a challenging endeavor. Even with powerful accelerators, successful fusion events are rare. The newly formed superheavy elements are highly unstable, existing for only fleeting moments. For instance, oganesson (element 118) and tennessine (element 117) were observed for only fractions of a second before decaying.
The Search for the Island of Stability
Despite the fleeting existence of most superheavy elements, theoretical predictions suggest the possibility of an “Island of Stability.” This concept proposes a region on the chart of nuclides where specific combinations of protons and neutrons could result in significantly longer-lived superheavy elements. The underlying theory is based on the nuclear shell model, which posits that atomic nuclei, much like electrons in an atom, are arranged in shells.
Nuclei with filled proton or neutron shells, corresponding to “magic numbers,” are predicted to exhibit enhanced stability. For superheavy elements, theoretical magic numbers are often predicted around 114, 120, or 126 protons, and 184 neutrons. A nucleus with both a magic number of protons and neutrons is considered “doubly magic,” and would be particularly stable. Flerovium-298 (114 protons, 184 neutrons) and unbihexium-310 (126 protons, 184 neutrons) are prime candidates for enhanced stability within this theoretical island. If such an island exists, the elements within it might have half-lives ranging from minutes or days to millions of years, enabling more extensive study and potentially new applications.
The Ultimate Limits of Elements
The search for new elements also involves understanding the ultimate physical boundaries to their existence. One theoretical limit is defined by the “drip lines,” which mark the point at which a nucleus can no longer hold onto additional protons or neutrons. Beyond the proton drip line, adding more protons causes the nucleus to immediately emit a proton due to overwhelming electrostatic repulsion. Similarly, beyond the neutron drip line, a nucleus spontaneously emits a neutron.
While the proton drip line is relatively well-established for many elements, the neutron drip line is known experimentally only for lighter elements up to neon. Beyond these theoretical limits, practical challenges also constrain the discovery of new elements. The increasing difficulty and expense of synthesizing ever-heavier elements, combined with their extremely short half-lives, make their detection and detailed study increasingly demanding. This ongoing scientific quest continues to push these boundaries, providing deeper insights into the fundamental forces that govern atomic nuclei.