Currently, the International Union of Pure and Applied Chemistry (IUPAC) officially recognizes and names 118 distinct chemical elements, from Hydrogen (Z=1) to Oganesson (Z=118). A chemical element is a specific type of atom defined exclusively by the number of protons contained within its nucleus, a value known as the atomic number (\(Z\)). Every atom with a unique atomic number, such as Carbon (Z=6) or Gold (Z=79), represents a different element. Therefore, the current count is 118, determined by the elements scientists have successfully discovered or created.
The Periodic Table: Defining the Current Count
The periodic table serves as the organizational framework for all known elements, systematically arranging them by increasing atomic number (\(Z\)). This organization reflects the repeating patterns in chemical properties. The current periodic table is complete up to the seventh row, or period, ending with Oganesson (Z=118).
Of these 118 elements, the vast majority are naturally occurring, found in measurable quantities on Earth. Natural elements span from Hydrogen (Z=1) up to Uranium (Z=92), with two exceptions. Technetium (\(Z=43\)) and Promethium (\(Z=61\)) are not naturally abundant because all their isotopes are radioactive and decay quickly.
The Distinction Between Natural and Synthetic Elements
Elements with an atomic number greater than 92 are known as transuranium elements, representing the transition to synthetic creation. These elements are not found in significant natural quantities due to their inherent nuclear instability, which causes them to decay rapidly. Neptunium (\(Z=93\)) and Plutonium (\(Z=94\)) were the first transuranium elements created, though trace amounts of both can be found in uranium ores.
The creation of heavier elements requires laboratory methods, such as nuclear reactors or particle accelerators. In a nuclear reactor, lighter target nuclei are bombarded with neutrons, which are captured to form unstable isotopes. These isotopes then undergo beta decay, where a neutron converts into a proton, thereby increasing the atomic number. For the heaviest elements, scientists use particle accelerators to smash a beam of light nuclei into a target of heavy nuclei. This high-speed fusion allows for the synthesis of the heaviest elements, such as those from \(Z=113\) to \(Z=118\).
Cosmic Forge: The Universal Origin of Elements
The elements in the universe originated from processes on a cosmological scale, known as nucleosynthesis. The lightest elements—Hydrogen (\(Z=1\)), Helium (\(Z=2\)), and trace amounts of Lithium (\(Z=3\))—were forged in the immediate aftermath of the Big Bang. These three primordial elements account for approximately 98% of the observable matter in the cosmos.
All elements heavier than Lithium were later created within stars through stellar nucleosynthesis. In massive stars, nuclear fusion combines lighter elements to create progressively heavier ones, starting with Helium fusing into Carbon, then Oxygen, and continuing up the periodic table. This fusion process releases the energy that powers stars and continues until Iron (\(Z=26\)), the point where fusion no longer releases energy.
Elements heavier than Iron require far more violent and energetic environments to form. They are created primarily during explosive events like supernovae and the merger of two neutron stars. These events initiate a rapid neutron-capture process (the r-process), which quickly builds up the heaviest elements and scatters them across the galaxy.
Theoretical Limits and the Search for Superheavy Elements
The theoretical question of whether the periodic table has an absolute end is a matter of nuclear physics. Scientists are actively searching for elements \(Z=119\) and \(Z=120\) to begin the eighth period of the table. The concept of an “Island of Stability” predicts that certain superheavy elements, such as those around \(Z=114\), \(Z=120\), or \(Z=126\), might have isotopes with significantly longer half-lives than their neighbors. This stability is attributed to specific numbers of protons and neutrons, called “magic numbers,” which create a closed-shell configuration in the nucleus.
There is a physical limit to how many protons a nucleus can hold before electrical repulsion overcomes the strong nuclear force. Theoretical calculations, which account for relativistic effects on orbiting electrons, suggest this limit is around atomic number \(Z=173\). At this point, the innermost electrons would need to move near the speed of light, fundamentally changing the atom’s structure and preventing the formation of a stable, neutral atom. Beyond this boundary, the possibility of a traditional chemical element ceases to exist.