We think of the periodic table as a static object that is the same in all textbooks. In the periodic tables that appear in our freshman chemistry book, for instance, the ionization energy of each element, the energy needed to remove an outer electron from the atoms, is a trait that we see as fixed — and therefore, an immutable property of each element. However, scientists today are making discoveries that can rearrange the periodic table of elements as we know it. Even the positions of some elements may not remain where they currently are in the table.
Most naturally occurring elements in the periodic table have long lifetimes and are therefore easy to study. The heaviest elements, however, are not found in nature. One example is lawrencium. Lawrencium appears at the bottom right corner of the periodic table, at the end of the row called the actinides, which also contains the well-known elements uranium and plutonium. The ionization energy of lawrencium has been theoretically predicted to be lower than that of the other actinides (Sato et al), but it has never been measured due to the difficulty of producing this massive element.
Scientists at the Japan Atomic Energy Agency have created lawrencium-256 atoms by bombarding californium atoms with energetic boron ions from an accelerator (Sato et al). It takes a few seconds to produce just one atom of lawrencium-256, and the atoms have a half-life of just 27 seconds, (Sato et al) so just moments are available to study their properties, a single atom at a time. The researchers were able to use an efficient detection system to successfully measure the first ionization energy of lawrencium-256. They published their results in the April 2015 issue of Nature (Sato et al). The team found that lawrencium does have an extremely low ionization energy, close in value to the theoretical prediction (Sato et al).
Some scientists have long believed that lawrencium is misplaced in the periodic table and actually belongs at the left side where elements with low ionization energy, such as sodium and magnesium, reside — under column three with elements such as scandium and ytterbium (Gray, Jenson). Other chemists still believe that lawrencium is correctly placed in the actinides section (Gray, Lavelle). These new measurements have reinvigorated this controversy. This would not change the way the periodic table would look at first glance, but the positions of four elements would be altered.
Lutetium, which is currently placed directly above lawrencium at the end of the row called the lanthanides, may exhibit similar properties, making it another candidate for column three (Gray). Lanthanum and actinium, which currently reside in column three of the periodic table would then be switched to head the lanthanide and actinide rows (Gray, Jenson). Will lawrencium and lutetium get catapulted to new spots in the periodic table? Stay tuned.
Gray, Richard, “Is the periodic table WRONG?” http://www.dailymail.co.uk/sciencetech/article-3033570/Is-periodic-table-WRONG-Elements-need-reordered-scientists-Lawrencium-looks-place.html
Jenson, W. B., “The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table: an update,” Foundations of Chemistry, March 2015. http://rd.springer.com/article/10.1007%2Fs10698-015-9216-1
Lavelle, L (2008) Lanthanum (La) and actinium (Ac) should remain in the d-block. J. Chem. Educ. 85: pp. 1482-1483 http://www.chemistry.ucla.edu/sites/default/files/publications/scerri/publication-download_publication_id_1005561
Sato, T. K., et al, “Measurement of the first ionization potential of lawrencium, element 103,” Nature, 2015, 520, 209, http://www.nature.com/nature/journal/v520/n7546/full/nature14342.html