The periodic table organizes all known chemical elements based on the number of protons in their atomic nucleus. While many elements have existed since the formation of the Earth, a significant number are not naturally occurring and exist only because of human scientific endeavor. Of the 118 elements currently recognized, approximately 24 are considered exclusively man-made, or synthetic. These elements do not appear in nature and are solely the result of high-energy laboratory experiments.
The Natural Limit and the Count
A chemical element is defined as “man-made” or synthetic if it is not found in the Earth’s crust or atmosphere in any meaningful quantity. The boundary between natural and man-made elements is generally drawn at element 92, uranium, the heaviest element found in substantial amounts on Earth. Neptunium (93) and plutonium (94) complicate this division. These two elements were first created in a laboratory, but trace amounts occur naturally in uranium ores as a result of spontaneous nuclear reactions. The purely synthetic elements are those with atomic numbers 95 through 118, spanning from americium to oganesson, which have no confirmed natural existence.
Creating Synthetic Elements
Creating heavy synthetic elements requires overcoming the Coulomb force, the electrical repulsion between positively charged protons. To fuse two nuclei into a single, heavier nucleus, scientists must accelerate them to immense speeds so the strong nuclear force can briefly overpower the repulsive electrical force. This process is carried out in specialized machines called particle accelerators, such as cyclotrons and synchrotrons.
The technique involves a “target and projectile” method. A beam of lighter nuclei (the projectile) is accelerated and directed at a fixed sheet of a heavy element (the target). For example, researchers might accelerate calcium (20 protons) into californium (98 protons) to create element 118. This collision is extremely inefficient; trillions of projectile atoms must be fired, often resulting in the detection of only a few atoms of the new element.
Shared Characteristics of Man-Made Elements
All synthetic elements share a high degree of instability and intense radioactivity. These heavy nuclei have too many protons and neutrons to remain intact for long. Instability is measured by the half-life, the time it takes for half of a sample of the element to decay into a different substance. For the heaviest synthetic elements, the half-life is measured in fractions of a second; Oganesson (Element 118) has a half-life of less than one millisecond.
Because the atoms exist for such a short duration, they cannot be collected or studied directly using conventional chemical methods. Their existence is confirmed by observing a predictable sequence of radioactive disintegrations known as a decay chain. When a newly formed superheavy atom decays, it transforms into a slightly lighter element, and the process continues until a known, stable element is reached. Scientists use sensitive detectors to track the unique “signature” of this decay cascade, proving the original synthetic element was briefly formed.