A synthetic element is a chemical element that does not occur naturally on Earth and can only be created artificially through human-induced nuclear reactions. These elements are highly unstable and decay radioactively into other elements within timeframes ranging from millions of years to fractions of a millisecond. In the Modern Periodic Table, while the first 94 elements occur naturally (though some only in trace amounts through radioactive decay), all elements with atomic numbers 95 through 118 are strictly synthetic. The creation and confirmation of these elements are overseen globally by the International Union of Pure and Applied Chemistry (IUPAC).
The Discovery Frontier: Technetium and Promethium
While most synthetic elements possess high atomic numbers and are positioned at the bottom of the periodic table, there are two distinct anomalies located within the main body of the table. These lighter elements have no stable isotopes, creating gaps in the sequence of naturally occurring elements.
- Technetium (Te, Z = 43): Technetium was the first element to be produced artificially. It was synthesized in 1937 by Carlo Perrier and Emilio Segrè by bombarding a Molybdenum sample with deuterons. Its name is derived from the Greek word tekhnetos, meaning “artificial.”
- Promethium (Pm, Z = 61): Positioned within the Lanthanide series, Promethium was first systematically isolated in 1945 at the Oak Ridge National Laboratory as a byproduct of uranium fission.
Transuranic Elements
Elements that succeed Uranium (Z = 92) in the periodic table are classified as Transuranic Elements. Every transuranic element is synthetic and radioactive. They are synthesized by bombarding heavy target nuclei (such as Uranium or Plutonium) with neutrons or lighter atomic nuclei in nuclear reactors and particle accelerators.
The Actinide Transuranics (Z = 93 to $103$)
This group completes the $5felectron subshell. Key examples include: </p> <ul> <li> <b>Neptunium (\text{Np},Z=93) and Plutonium (\text{Pu},Z=94):</b> Sourced initially by bombarding Uranium-238 with neutrons. While trace amounts of Plutonium-239 can form naturally in uranium ores via neutron capture, it is considered a synthetic element for practical and industrial purposes. </li> <li> <b>Americium (\text{Am},Z=95) and Curium (\text{Cm},Z=96):</b> Created during the Manhattan Project by exposing plutonium to intense neutron radiation. </li> </ul> <h5>Superheavy Elements / Transactinides (Z = 104to %%MONEYBLOCK1%%)</h5> <p> Elements following the Actinide series (Z \ge 104) are known as <b>Superheavy Elements</b> or <b>Transactinides</b>. They occupy the %%MONEYBLOCK4%%d and $7psubshells in the 7th period. </p> <ul> <li> <b>Synthesis Method:</b> These elements cannot be produced in standard nuclear reactors because their nuclei are too unstable to undergo successive neutron captures. Instead, they are synthesized using heavy-ion colliders, where target atoms (like Californium or Lead) are bombarded with high-energy projectiles (like Calcium-48 ions) to overcome the electrostatic repulsion between the nuclei. </li> </ul> <h4>The Complete List of Period 7 Synthetic Elements</h4> <table> <thead> <tr> <td><strong>Atomic Number (Z)</strong></td> <td><strong>Element Name</strong></td> <td><strong>Symbol</strong></td> <td><strong>Discovering/Naming Affiliation</strong></td> <td><strong>Key Stability/Half-Life Metric</strong></td> </tr> </thead> <tbody> <tr> <td><b>95</b></td> <td>Americium</td> <td>\text{Am}</td> <td>Lawrence Berkeley Lab, USA</td> <td>^{243}\text{Am}(\approx 7,370years)</td> </tr> <tr> <td><b>96</b></td> <td>Curium</td> <td>\text{Cm}</td> <td>Lawrence Berkeley Lab, USA</td> <td>^{247}\text{Cm}(\approx 1.56 \times 10^7years)</td> </tr> <tr> <td><b>97</b></td> <td>Berkelium</td> <td>\text{Bk}</td> <td>University of California, Berkeley</td> <td>^{247}\text{Bk}(\approx 1,380years)</td> </tr> <tr> <td><b>98</b></td> <td>Californium</td> <td>\text{Cf}</td> <td>University of California, Berkeley</td> <td>^{251}\text{Cf}(\approx 900years)</td> </tr> <tr> <td><b>99</b></td> <td>Einsteinium</td> <td>\text{Es}</td> <td>Discovered in thermonuclear debris</td> <td>^{252}\text{Es}(\approx 471days)</td> </tr> <tr> <td><b>100</b></td> <td>Fermium</td> <td>\text{Fm}</td> <td>Discovered in thermonuclear debris</td> <td>^{257}\text{Fm}(\approx 100.5days)</td> </tr> <tr> <td><b>101</b></td> <td>Mendelevium</td> <td>\text{Md}</td> <td>Named after Dmitri Mendeleev</td> <td>^{258}\text{Md}(\approx 51.5days)</td> </tr> <tr> <td><b>102</b></td> <td>Nobelium</td> <td>\text{No}</td> <td>Named after Alfred Nobel</td> <td>^{259}\text{No}(\approx 58minutes)</td> </tr> <tr> <td><b>103</b></td> <td>Lawrencium</td> <td>\text{Lr}</td> <td>Named after Ernest Lawrence</td> <td>^{266}\text{Lr}(\approx 11hours)</td> </tr> <tr> <td><b>104</b></td> <td>Rutherfordium</td> <td>\text{Rf}</td> <td>Joint Institute for Nuclear Research</td> <td>^{267}\text{Rf}(\approx 1.3hours)</td> </tr> <tr> <td><b>105</b></td> <td>Dubnium</td> <td>\text{Db}</td> <td>Named after Dubna, Russia</td> <td>^{268}\text{Db}(\approx 28hours)</td> </tr> <tr> <td><b>106</b></td> <td>Seaborgium</td> <td>\text{Sg}</td> <td>Named after Glenn T. Seaborg</td> <td>^{269}\text{Sg}(\approx 3.1minutes)</td> </tr> <tr> <td><b>107</b></td> <td>Bohrium</td> <td>\text{Bh}</td> <td>Named after Niels Bohr</td> <td>^{270}\text{Bh}(\approx 61seconds)</td> </tr> <tr> <td><b>108</b></td> <td>Hassium</td> <td>\text{Hs}</td> <td>GSI Helmholtz Centre, Germany</td> <td>^{277}\text{Hs}(\approx 30seconds)</td> </tr> <tr> <td><b>109</b></td> <td>Meitnerium</td> <td>\text{Mt}</td> <td>Named after Lise Meitner</td> <td>^{278}\text{Mt}(\approx 8seconds)</td> </tr> <tr> <td><b>110</b></td> <td>Darmstadtium</td> <td>\text{Ds}</td> <td>Named after Darmstadt, Germany</td> <td>^{281}\text{Ds}(\approx 11seconds)</td> </tr> <tr> <td><b>111</b></td> <td>Roentgenium</td> <td>\text{Rg}</td> <td>Named after Wilhelm Röntgen</td> <td>^{282}\text{Rg}(\approx 2.1minutes)</td> </tr> <tr> <td><b>112</b></td> <td>Copernicium</td> <td>\text{Cn}</td> <td>Named after Nicolaus Copernicus</td> <td>^{285}\text{Cn}(\approx 29seconds)</td> </tr> <tr> <td><b>113</b></td> <td>Nihonium</td> <td>\text{Nh}</td> <td>RIKEN Institute, Japan</td> <td>^{286}\text{Nh}(\approx 20seconds)</td> </tr> <tr> <td><b>114</b></td> <td>Flerovium</td> <td>\text{Fl}</td> <td>Flerov Laboratory, Russia</td> <td>^{289}\text{Fl}(\approx 2.6seconds)</td> </tr> <tr> <td><b>115</b></td> <td>Moscovium</td> <td>\text{Mc}</td> <td>Named after Moscow region, Russia</td> <td>^{290}\text{Mc}(\approx 0.8seconds)</td> </tr> <tr> <td><b>116</b></td> <td>Livermorium</td> <td>\text{Lv}</td> <td>Lawrence Livermore Lab, USA</td> <td>^{293}\text{Lv}(\approx 61milliseconds)</td> </tr> <tr> <td><b>117</b></td> <td>Tennessine</td> <td>\text{Ts}</td> <td>Named after Tennessee region, USA</td> <td>^{294}\text{Ts}(\approx 80milliseconds)</td> </tr> <tr> <td><b>118</b></td> <td>Oganesson</td> <td>\text{Og}</td> <td>Named after Yuri Oganessian</td> <td>^{294}\text{Og}(\approx 0.7milliseconds)</td> </tr> </tbody> </table> <h4>Nuclear Stability and the “Island of Stability”</h4> <p> The primary limiting factor in the synthesis of superheavy elements is their rapid decay, driven by spontaneous fission and alpha particle emission. As the number of protons (Z) increases, the electrostatic repulsion between them rapidly overcomes the attractive strong nuclear force that holds the nucleus together. </p> <h5>The Conceptual Concept</h5> <p> Nuclear physicists utilize the <b>Shell Model of the Nucleus</b> to predict structural stability. Similar to how chemical noble gases exhibit exceptional stability when their electron shells are completely filled, atomic nuclei exhibit enhanced stability when they contain specific “magic numbers” of protons or neutrons (such as 2, 8, 20, 28, 50, and 82). </p> <h5>The Island of Stability</h5> <p> This theoretical model predicts an <b>“Island of Stability”</b> in the superheavy region of the periodic table. It is hypothesized that superheavy isotopes with a specific combination of protons (potentiallyZ=114, 120,or %%MONEYBLOCK2%%) and neutrons (N=184) will form closed, stable nuclear shells. While elements like Flerovium and Oganesson decay in fractions of a second, isotopes located closer to the center of this hypothetical island might possess half-lives extending for minutes, days, or even years, allowing for more detailed study of their chemical and physical properties. </p> <h4>Practical and High-Yield Industrial Applications</h4> <p> Despite their instability and high production costs, several synthetic elements play critical roles across medicine, industry, and scientific research. </p> <h5>Technetium-99m (\text{Tc}-99\text{m}) in Nuclear Medicine</h5> <p> The metastable nuclear isomer Technetium-99m is the most widely used radioactive tracer in modern diagnostic medicine. </p> <ul> <li> It emits readily detectable, low-energy gamma rays without harmful beta radiation. </li> <li> It possesses a short half-life of 6 hours, ensuring it clears rapidly from the patient’s body. </li> <li> It is bound to specific carrier molecules to map blood flow and diagnose pathologies in the human heart, brain, thyroid, and skeletal systems. </li> </ul> <h5>Americium-241 (\text{Am}-241) in Domestic Smoke Detectors</h5> <p> Americium-241 is used inside conventional ionization smoke detectors. </p> <ul> <li> It emits alpha particles that ionize the air molecules inside a small sensing chamber, creating a continuous, weak electric current. </li> <li> When smoke particles enter the chamber, they attach to the ionized air molecules and disrupt the electrical current, triggering the alarm system. </li> </ul> <h5>Californium-252 (\text{Cf}-252) as a Neutron Source</h5> <p> Californium-252 undergoes spontaneous fission at a fixed, highly predictable rate, making it an intense and compact source of neutrons. </p> <ul> <li> It is used in <b>Neutron Activation Analysis (NAA)</b> to inspect luggage and cargo containers for explosives or fissile materials. </li> <li> It is used as a portable neutron source to ignite nuclear reactors and to analyze moisture content in soil layers during geological oil well logging. </li> </ul> <h5>Plutonium-238 (\text{Pu}-238$) in Deep-Space Exploration
Plutonium-238 emits steady alpha radiation as it decays, generating significant thermal energy. This heat is converted into electricity using thermocouples within Radioisotope Thermoelectric Generators (RTGs).
- Because solar energy diminishes rapidly in the outer solar system, RTGs serve as the primary long-term power source for deep-space missions.
- Notable applications include powering NASA’s Voyager probes, the Cassini spacecraft, and the Curiosity and Perseverance Mars rovers.