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Physical Chemistry

Lawrencium Ionization Energy Measured

Actinides: Study confirms theoretical understanding of electronic structure of superheavy elements

by Jyllian Kemsley
April 9, 2015 | APPEARED IN VOLUME 93, ISSUE 15

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Credit: Nature
The first ionization energy for each element in the periodic table is represented by bar height. Energies for elements with blue symbols are theoretical predictions.
09315-notw3-periodictablecxd.jpg
Credit: Nature
The first ionization energy for each element in the periodic table is represented by bar height. Energies for elements with blue symbols are theoretical predictions.

Researchers have for the first time measured the first ionization energy of lawrencium, the last of the actinides, validating predictions of the element’s electronic structure (Nature 2015, DOI: 10.1038/­nature14342).

The first ionization energy is the energy required to remove one electron from a neutral atom in the gaseous state.

Compared with lighter members of the periodic table, the large nuclear charge for elements in rows six and seven causes their orbiting electrons to move faster. The speeding electrons generate relativistic effects that alter orbital energy levels.

Determining first ionization energies experimentally helps to ensure that researchers understand relativistic effects theoretically. Unfortunately, the superheavy elements with the greatest effects are also the most difficult to study because the elements can only be created through fusion reactions at heavy-ion accelerators and have short half-lives.

Lawrencium is now the heaviest element to have its first ionization energy determined experimentally. An international team led by Tetsuya K. Sato and Yuichiro Nagame of the Japan Atomic Energy Agency fired a 11B beam at a 249Cf target to produce 256Lr, which has a half-life of 27 seconds.

Sato, Nagame, and colleagues found that lawrencium’s first ionization energy is 4.96 eV, similar to those for group 1 of the periodic table. The predicted electronic configuration of Lr is [Rn]5f147s27p1/21 (the energies of p orbitals split from relativistic effects).

“This work represents a very important benchmark for testing theory predictions and validating computations for other atomic properties and other superheavy systems,” says Marianna Safronova, a physics professor at the University of Delaware.

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Comments
Eric Scerri (April 9, 2015 9:56 PM)

There seems to be a good deal of confusion concerning this article and what it means for the on-going question of the constitution of group 3 of the periodic table. According to a an on-line news report from Nature Magazine, the measurement of the ionization energy of Lr is interpreted by some of the authors of the paper to confirm that Lr is the first member of the f-block, while the lead author seems to think it supports placing Lr in the d-block!

http://www.nature.com/news/exotic-atom-struggles-to-find-its-place-in-the-periodic-table-1.17275

In my recent book, "A Very Short Introduction to the Periodic Table", published by OUP, I proposed a categorical argument in favor of group 3 being Sc, Y, Lu, Lr. This argument does not depend on measuring any particular property of any of these elements. If the periodic table is presented in the more correct 32-column or long-format, and if one maintains the order of increasing atomic numbers throughout the table, one is inevitably led to the conclusion that Lu and Lr belong to group 3 and that La and Ac should be placed at the start of the f-block elements. One can always return to a more familiar 18-column format but while retaining the group 3 arrangement of Sc, Y, Lu, Lr.

http://www.amazon.com/The-Periodic-Table-Short-Introduction/dp/0199582491/ref=sr_1_1?ie=UTF8&qid=1354680359&sr=8-1&keywords=eric+scerri

Eric Scerri, UCLA.
http://www.ericscerri.com

Eric Scerri (April 9, 2015 10:08 PM)
apologies I meant to write, some think that Lr should remain as the LAST member of the f-block.

eric scerri
Jerome Zoeller (April 17, 2015 8:37 AM)



This is the sort of question that Frank Cotton could have clarified. Elucidatiion will undoubtedly follow with a quantum mechanics approach. It IS an excellent question that requires reanalysis of several lanthanides

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