Measurement of the first ionization potential of lawrencium, element 103

Lawrencium, with atomic number 103, has an isotope with a half-life of 27 seconds; even so, its first ionization potential has now been measured on an atom-at-a-time scale and agrees well with state-of-the-art theoretical calculations that include relativistic effects. The chemistry of element 103 The most dramatic modern revision of Mendeleev's periodic table of elements came in 1944 when Glenn T. Seaborg placed a new series of elements, the actinides (atomic numbers 89–103), below the lanthanides. In this issue of Nature , Yuichiro Nagame and colleagues report the first measurement of one of the basic atomic properties of element 103 (lawrencium), namely its first ionization potential. Lawrencium is only accessible via atom-at-a-time synthesis in heavy-ion accelerators, so experimental investigations of its properties are rare. Nagame and colleagues were able to reduce the number of atoms required to measure the ionization potential from billions to thousands, and these results — in agreement with the latest theoretical calculations — show that the last valence electron in lawrencium is the most weakly bound one in all actinides and any other element beyond group 1 of the periodic table. This signature — in a region of the periodic table where the sheer size of the atoms means that relativistic effects play a crucial role — confirms the end of the actinide series at element 103. The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row—including the actinides—even affecting ground-state configurations 1 , 2 . Atomic s and p 1/2 orbitals are stabilized by relativistic effects, whereas p 3/2 , d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP 1 ) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP 1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by the difficulty in obtaining the heaviest elements on scales of