The periodic table of elements serves as a fundamental organizational chart for chemistry, arranging all known chemical elements in a tabular array. This structure is based primarily on the atomic number, which is the count of protons found within the nucleus of an atom. Every element is uniquely defined by this proton count, meaning any change in the number of protons creates a completely new substance with different properties. The central question in modern physics and chemistry is whether this sequence of unique elements continues indefinitely or if there is a finite limit to the size an atomic nucleus can reach.
The Confirmed Roster of Elements
The periodic table currently contains 118 elements, from hydrogen (1) to oganesson (118). This roster is considered structurally complete because the table is organized into seven horizontal rows, or periods, and element 118 completes the seventh period. The International Union of Pure and Applied Chemistry (IUPAC), the global authority for chemical standards, confirmed the completion of this seventh row in 2016.
IUPAC’s process for adding a new element is rigorous, requiring verification by independent laboratories and scrutiny by a Joint Working Party. The discovery must be confirmed through several methods, such as cross-reactions, which involve creating the same element through two different combinations of lighter nuclei. Once the discovery is confirmed, the collaborating research teams are invited to propose a permanent name and symbol, which must then pass a public review before final approval by the IUPAC Council.
Synthesizing New Elements
Elements beyond uranium (92 protons) are not found in nature and must be created artificially in laboratories. These elements, often called superheavy or transactinide elements, require specialized facilities like powerful particle accelerators for synthesis. The accelerators are necessary to overcome the natural repulsive forces within the atom.
The most common method is nuclear fusion, which involves directing a beam of ions from a lighter element into a heavier target. For instance, to create oganesson (element 118), scientists used a beam of calcium ions (20 protons) directed at a target of californium (98 protons). This collision must be precise, accelerating the lighter nuclei to about one-tenth the speed of light to briefly overcome the electrostatic repulsion between the positively charged nuclei.
The resulting superheavy nuclei are extremely unstable and are not produced in macroscopic samples. Their existence is confirmed only by detecting the unique, characteristic decay chains that occur instantly after formation. These elements are highly radioactive, with half-lives often measured in milliseconds or even microseconds.
The Theoretical Edge: Limits to Atomic Existence
The increasing instability of superheavy elements is due to the fundamental forces at work within the nucleus. As the atomic number climbs, the number of positively charged protons increases, leading to a much stronger electrostatic repulsion that attempts to tear the nucleus apart. This repulsive force is only counteracted by the strong nuclear force, which acts over a very short range to bind protons and neutrons together. However, the strong force cannot indefinitely overcome the electrostatic repulsion as the nucleus grows larger.
Theoretical physics suggests that the maximum possible size for an atom may be limited by relativistic effects related to the speed of electrons. Calculations, which account for the finite size of the atomic nucleus, place the most probable highest atomic number at around 172. Beyond this point, the electrical field of the nucleus would be so intense that the innermost electrons would be pulled into the nucleus, making the formation of a conventional, neutral atom impossible.
The most compelling theoretical concept driving current research is the “Island of Stability.” This hypothesis predicts that certain combinations of protons and neutrons, known as “magic numbers,” could create a closed-shell configuration in the nucleus, similar to how noble gases have stable electron shells. Elements potentially located on this island, such as those around atomic numbers 120 or 126, are theorized to be significantly more stable than their immediate neighbors, perhaps exhibiting half-lives of minutes, days, or possibly even longer. This temporary respite from instability is a primary goal for physicists seeking to extend the periodic table.
Is the Periodic Table Truly Complete?
The periodic table is currently considered structurally complete because the seventh period is entirely filled with confirmed elements up to oganesson (atomic number 118). This means the organizational framework of the known table is fully populated according to the principles of electron shells and chemical periodicity.
The table is not theoretically complete, however, as no physical law prevents the creation of elements beyond 118. Scientists are actively pursuing the synthesis of elements 119 and 120, which would begin the eighth period. The primary challenge is the practical difficulty of synthesis; reactions are extremely inefficient, and the resulting nuclei are increasingly short-lived.
The search for the “Island of Stability” confirms the belief that the table can be extended, even if the new elements are only briefly detectable. The underlying principle of increasing atomic number suggests the potential for new periods. Future discoveries will likely slow dramatically due to the immense energy and time required to produce and confirm just a few atoms of these transient superheavy elements.