Transactinides


What are transactinides?

How do you make transactinides?

How do you perform chemistry with single atoms?

What can we learn from these experiments?

Why is this interesting?


What are transactinides?

Transactinides are elements in the periodic table with numbers >104. Element 103, Lawrencium, has a filled 5f electron shell. The known transactinides (elements 104 to 112) form the 4th transition series in the periodic table. The lately IUPAC recommended names are:

For the elements 110, 111 and 112 there are no proposed names yet. Some facts about the elements you can find here.

How do you make transactinides?

Transactinides are produced in heavy ion reactions. For example, at GSI Darmstadt, at the Paul Scherrer Institut Villigen (Switzerland) or at the Lawrence Berkeley Laboratory. There are only single atoms produced in such reactions. Because these have quite short half lives, one really has to deal with single atoms while doing chemistry.

How do you perform chemistry with single atoms?

Doing chemistry with single atoms requires an answer to the question whether single atoms behave exactly like macroscopic amounts. Macroscopic amounts often show a kind of equilibrium. For example, a substance can be partly dissolved, partly precipated; a liquid evaporates slowly (it is in equilibrium with the gaseous phase); weak acids are partly dissociated and so on.

So the question is: What does a single atom in such a case? One atom can not be in two states at the same time. What does a "concentration" mean in equilibrium constants? Guillaumont showed that in this case, concentrations change into probabilities to find the atom in the referred state. That means: If I use conditions in single atom experiments which lead quickly to an equilibrium, the properties of a single atom are representative for the element.

Hence, chromatographic methods (HPLC) are ideal for this type of experiments. Because of the relative low activation energy of adsorption and desorption in chromatographic systems the equilibrium is reached quickly. A single atom in a HPLC column changes many times from the mobile phase into the stationary one and vice versa. So the retention time is characteristic for the chemical behaviour of the species. An automated chromatography apparatus used for such purposes is ARCA.

What can we learn from these experiments?

The short half lives of the heavy elements restricts the number of possible chemical conclusions. The first examination of transactinides should help to decide whether the element behaves like the other members of the group in the periodic table. The next logical step is to find out, which element in the group is the most similar one.

Examinated properties are, for example, volatilities of the Halogenides, extraction behaviour on different extraction chromatography columns and ion exchange resins. These are determined by the stochiometry of the compounds which can therefore be derived.

Why is this interesting?

The Quantum theory can predict properties of heavy elements. So results of experiments can prove that quantum effents are well understood. Escpecially interesting are the consequences of the relativistic effects:

Caused by the high nuclear charge the electrons "move" (in the classical interpretation) so fast, that the velocity is near the speed of light. The equivalence of mass and energy (relativity) lets the mass of the electron increase. This causes certain orbitals to change their size and necessarily atomic properties. This "relativistic effect" is well known from the further period and can be given as the reason for the colour of gold (which is unique among metals) or the liquidity of mercury. It is expected that the relativistic effects are so strong for heavy transactinides that the group classification becomes meaningless.

Some articles about chemical behaviour of transactinides:

Latest results of element 106 chemistry:


Links:


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October 1997 by Erik Strub.