How Are New Elements Discovered?

New Elements and the Periodic Table

New elements may be found to fill in gaps and add to the periodic table.
New elements may be found to fill in gaps and add to the periodic table. Jaap Hart, Getty Images

Dmitri Mendeleev is credited with making the first periodic table that resembles the modern periodic table. His table ordered the elements by increasing atomic weight (we use atomic number today). He could see recurring trends, or periodicity, in the properties of the elements. His table could be used to predict the existence and characteristics of elements that hadn't been discovered.

When you look at the modern periodic table, you won't see gaps and spaces in the order of the elements. New elements aren't exactly discovered anymore. However, they can be made, using particle accelerators and nuclear reactions. A new element is made by adding a proton (or more than one) or neutron to a pre-existing element. This can be done by smashing protons or neutrons into atoms or by colliding atoms with each other. The last few elements in the table will have numbers or names, depending on which table you use. All of the new elements are highly radioactive. It's difficult to prove that you have made a new element, because it decays so quickly.

Key Takeaways: How New Elements Are Discovered

  • While researchers have found or synthesized elements with atomic number 1 through 118 and the periodic table appears full, it's likely additional elements will be made.
  • Superheavy elements are made by striking pre-existing elements with protons, neutrons, or other atomic nuclei. The processes of transmutation and fusion are used.
  • Some heavier elements are likely made within stars, but because they have such short half-lives, they haven't survived to be found on Earth today.
  • At this point, the problem is less about making new elements than detecting them. The atoms that are produced often decay too quickly to be found. In some cases, verification might come from observing daughter nuclei that have decayed but couldn't have resulted from any other reaction except using the desired element as a parent nucleus.

The Processes That Make New Elements

The elements found on Earth today were born in stars via nucleosynthesis or else they formed as decay products. All of the elements from 1 (hydrogen) to 92 (uranium) occur in nature, although elements 43, 61, 85, and 87 result from radioactive decay of thorium and uranium. Neptunium and plutonium were also discovered in nature, in uranium-rich rock. These two elements resulted from neutron capture by uranium:

238U + n → 239U → 239Np → 239Pu

The key takeaway here is that bombarding an element with neutrons can produce new elements because neutrons can turn into protons via a process called neutron beta decay. The neutron decays into a proton and releases an electron and antineutrino. Adding a proton to an atomic nucleus changes its element identity.

Nuclear reactors and particle accelerators can bombard targets with neutrons, protons, or atomic nuclei. To form elements with atomic numbers greater than 118, it's not enough to add a proton or neutron to a pre-existing element. The reason is that the superheavy nuclei that far into the periodic table simply aren't available in any quantity and don't last long enough to be used in element synthesis. So, researchers seek to combine lighter nuclei that have protons that add up to the desired atomic number or they seek to make nuclei that decay into a new element. Unfortunately, because of the short half life and the small number of atoms, it's very hard to detect a new element, much less verify the result. The most likely candidates for new elements will be atomic number 120 and 126 because they are believed to have isotopes that might last long enough to be detected.

Superheavy Elements in Stars

If scientists use fusion to create superheavy elements, do stars also make them? No one knows the answer for certain, but it's likely stars also make transuranium elements. However, because the isotopes are so short-lived, only the lighter decay products survive long enough to be detected.

Sources

  • Fowler, William Alfred; Burbidge, Margaret; Burbidge, Geoffrey; Hoyle, Fred (1957). "Synthesis of the Elements in Stars." Reviews of Modern Physics. Vol. 29, Issue 4, pp. 547–650.
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  • Heenen, Paul-Henri; Nazarewicz, Witold (2002). "Quest for superheavy nuclei." Europhysics News. 33 (1): 5–9. doi:10.1051/epn:2002102
  • Lougheed, R. W.; et al. (1985). "Search for superheavy elements using 48Ca + 254Esg reaction." Physical Review C. 32 (5): 1760–1763. doi:10.1103/PhysRevC.32.1760
  • Silva, Robert J. (2006). "Fermium, Mendelevium, Nobelium and Lawrencium." In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 978-1-4020-3555-5.