Lawrencium Ionization Energy Measured

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]5f¹⁴7s²7p_1/2¹ (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.