The most fundamental goal in chemistry is the determination of the chemical properties of the elements. Information on the chemical properties of the heaviest elements can be used to assess the importance of relativistic effects in the valence electrons, and to refine theoretical calculations and our understanding of their chemical properties. Knowledge gained for the heaviest elements can be applied to understanding of chemical properties throughout the periodic table.

Isotopes of lawrencium (Lr, element 103) and heavier elements have half-lives of a few minutes or less, and can only be produced at accelerators. Production rates are low, ranging from one atom per minute to one atom per day. Because of these limitations, chemistry must be performed on single atoms, using extremely sensitive and specialized techniques. Therefore, relatively little is known about the chemistry of the heaviest elements. So far, there have been only five chemical experiments with seaborgium (Sg, element 106), one with bohrium (Bh, element 107), and one with hassium (Hs, element 108). For these three elements, only very general chemical properties have been measured, tentatively placing them in their groups 6, 7, and 8 of the periodic table, respectively. There have been a few dozen publications on experimental determination of the chemical properties of dubnium (Db, element 105) and rutherfordium (Rf, element 104). These more detailed results give tantalizing clues about the finer points of chemical bonding and stability of simple complexes, but are at times, contradictory.

Most of the heavy element chemical properties that have been measured to date resulted from experiments conducted by the LBNL team or where LBNL scientists played a substantial role in international collaborations (Germany, Switzerland, Russia, and Japan). These experiments represent the bulk of knowledge of chemical properties for six elements, from lawrencium (103) to hassium (108), and extended the periodic table by six percent. A brief summary of heavy element chemical knowledge is given in the appendix.

When producing isotopes of elements 103-108 at accelerators, large amounts of interfering radioactivities are produced concurrently. Until now, the most important aspect of a heavy element chemical separation was the need for an extremely efficient separation of the heavy element atoms from those interfering radioactivities. This severely limited the chemical reactions that could be used. We have pioneered the use of the Berkeley Gas-filled Separator (BGS) as a preseparator to provide high-purity heavy element samples for chemical separations. This allows a shift in priority when choosing a chemical reaction: the chemical reaction can now be chosen to better elucidate the heavy element chemical properties, rather than concentrating on removal of interfering activities.

In recent experiments, 257-Rf, an isotope of element 104 with a 4-second half-life, was produced and separated from other nuclear reaction products by the BGS. After stopping the Rf in a gas cell, it was transported to the chemical separation system with a gas-jet system. Rapid liquid-liquid extractions were carried out with an automated chemistry and detection system. These experiments demonstrated the large increase in sensitivity afforded by the use of the BGS as a preseparator. Taking advantage of these new capabilities, we are presently developing new liquid-liquid extraction and gas-phase chemical systems which will provide new insights into the chemical properties of Rf and Db (element 105).

For future experiments, we will develop a 244-Pu target capability for the BGS. Use of this 244-Pu target will allow access to longer-lived isotopes of Rf and Db, as well as isotopes of Sg (element 106), Bh (element 107), Hs (element 108), and possibly elements 112 and 114. Chemical reaction systematics of elements 104 through 108, and possibly 112 and 114, will be studied by liquid-liquid solvent extractions with organic extractants having different functional groups and extraction mechanisms; for example, chelate complexation via beta-diketonates and crown ethers, adduct formation with organophosphates, and liquid ion exchange with amines. Additionally, gas phase reactions with highly volatile organic compounds will be performed to measure reaction kinetics and thermodynamic adsorption enthalpies on various surface materials such as quartz and transition metal surfaces.

The combination of the versatile and reliable LBNL 88-Inch Cyclotron, with the world-leading ECR ion source development, and the highly efficient and selective Berkeley Gas-filled Separator, is ideally suited for studies of heavy element chemical properties. The LBNL Heavy Element Nuclear and Radiochemistry program will take full advantage of these new experimental opportunities in the study of the nuclear chemistry of the heaviest elements.