One-atom-at-a-time chemistry

This chapter is divided in four parts. The first one is devoted to thermodynamic considerations, the second deals with kinetic aspects and one-atom-at-a-time chemistry. Then, experimental approaches and finally effects of the media and their influence on aqueous chemistry will be discussed. 

The concept of one-atom-at-a-time chemistry is different from that of a single atom chemistry. The main difference is the time. An observable chemical reaction of a given radio nuclide can be defined with the following temporal quantities ... 

Problems associated with the disintegration of a single radioactive atom will not be developed here However, an understanding of the decay appears rather important in one-atom-at-a-time chemistry [2,10],... 

Since the SHE chemistry is correlated with one-atom-at-a-time chemistry, one may ask if it is meaningful to carry out experiments with a single atom. From a theoretical point of view, as it was demonstrated above, for a 1 1 stoichiometry reaction the mass action law and the kinetics laws are valid. However, as there is no macrocomponent consumption, such reaction appears as of pseudo first order. Note that reactions with a 1 1 stoichiometry include all reactions between the microcomponent and a single macrocomponent. This concept can also be extended to stepwise reactions such as successive formation of metal complexes (hydrolysis, halide complexation) for example ... 

The feasibility of Kd determination in the context of one-atom-at-a-time chemistry is very promising since the collection of Kd values will allow to establish reliable variations of the chemical properties (complexation,... 

In this chapter, the special conditions of the synthesis and decay of the transactinides are considered followed by some remarks about performing chemistry with only one atom at a time (referred to therefore as one-atom-at-a-time chemistry or single-atom chemistry). The experimental techniques are outlined, and a description of theoretical predictions and experimental results on the chemistry of Rf, Db, Sg, Bh, Hs, and Cn is given and mutually compared. Perspectives to go beyond 112 are also briefly discussed. 

The actinides uranium and thorium occur in nature as primordial matter. Actinium and protactinium occur in nature as daughters of thorium and uranium, while small amounts of neptunium and plutonium are present as a result of neutron-capture reactions of uranium. All other members of the series are man-made. Separation chemistry has been central to the isolation and purification of the actinides since their discovery. The formation of the transplutonium actinides was established only as a result of chemical-separation procedures developed specifically for that purpose. The continued application of separation science has resulted in the availability of weighable quantities of the actinides to fermium. Separation procedures are central to one-atom-at-a-time chemistry used to identify synthetic trans-actinide (superheavy) elements to element 107 and above (Report of a Workshop on Transactinium Science 1990). 

The discovery and identification of element 101 (mendelevium, Md) was a landmark experiment in many ways [ 1 ]. It was the first new transuranium element to be produced and identified on the basis of one-atom-at-a-time chemistry and it is also the heaviest element (to date) to be chemically identified by direct chemical separation of the element itself. All of the higher Z elements have been first identified by physical/nuclear techniques prior to study of their chemical properties. In fact, one of the criteria for chemical studies is that an isotope with known properties be used for positive identification of the element being studied. Due to relativistic effects [1] chemical properties cannot be reliably predicted and a meaningful study of chemical properties cannot be conducted with both unknown chemistry and unknown, non-specific nuclear decay properties ... 

The chemical information deduced from these experiments, illustrative of one-atom-at-a-time chemistry, appears reliable. Intuitively, the numerous repetitive experiments give statistically significant results see Liquid-Phase Chemistry of SuperheavyElements and Gas-Phase Chemistry of Superheavy Elements for a comprehensive report of SHE chemistry experiments in the liquid-phase and gas-phase, respectively. The next paragraph will provide proof that kinetics and thermodynamics are valid at the atom scale for most chemical reactions performed with SHEs. 

However, reactions between Ei and E2 can only be observed if the half-life of El is compatible with the time characteristics of the reaction under study. For instance, the time needed to achieve the equilibrium must be shorter than the lifetime of the involved radionuclide. Studies of the chemical properties of SHEs give rise not only to the concept of single-atom chemistry but also to one-atom-at-a-time chemistry. For that purpose, chemical processes with high reaction rates are required. 

The feasibility of Kj determinations in the context of one-atom-at-a-time chemistry is very promising and the collection of Kj values will allow establishment of reliable variations of the chemical properties (complexation, hydrolysis) of elements within a group, for comparison with theoretical predictions, and, perhaps, for determination of thermodynamic constants. Moreover, other information can be derived from chromatography experiments. The mathematical treatment of elution curves can be carried out with various models, especially Glueckauf s, which offers the advantages of using simple equations and takes into account the possible dissymmetry of elution bands [31, 32]. The parameters included in Glueckauf s equations allow the determination of the distribution... 

Dr. Darleane C. Hoffman of the Nuclear Science Division of the Lawrence Berkeley National Laboratory and Department of Chemistry at the University of California at Berkeley has written and presented several papers documenting her work and that of her team on the laboratory production of transactinide and actinide elements one-atom-at-a-time. She explains the difficulty of determining the chemistry of heavy elements How long does an atom need to exist before it s possible to do any meaningful chemistry on it Is it possible to learn anything at all about the reactions of an element for which no more... 

This tiny quantity of material, if prepared as an aqueous solution of volume 1 L, would have a concentration of 10 14 mol/L. This simple calculation demonstrates a number of the important features of radiochemistry, that is, (a) the manipulation of samples involving infinitesimal quantities of material, (b) the power of nuclear analytical techniques (since 1 j.Ci is a significant, easily detectable quantity of radioactivity), and (c) in an extension of the calculation, since the decay of a single atom might occur by a-particle emission (with 100% detection efficiency), the ability to do chemistry one atom at a time. 

As the quantities of elements applied in nuclear chemistry are often small, down to one-atom-at-a-time, deposition and volatilization are predominately related to adsorption and desorption phenomena, respectively. Practically, pure condensed phases do not occur. The volatilization and the gas phase transport through a chromatography column depend on... 

The chemistry of superheavy elements always faces a one-atom-at-a-time situation - performing separations and characterizations of an element with single, short-lived atoms establishes one of the most extreme limits in chemistry. While large numbers of atoms and molecules are deeply inherent in the statistical approach to understanding chemical reactions as dynamic, reversible processes Chapter 3 discusses specific aspects how the behavior of single atoms mirrors properties of macro amounts. 

Single atom chemistry is of particular importance if only single atoms are available for chemical studies, as in the case of the heaviest elements. The short-lived isotopes of these elements can only be produced at a rate of one atom at a time, and the investigation of their chemical properties requires special considerations. 

D.C. Hoflinami and D.M. Lee (1999) Journal of Chemical Education, vol. 76, p. 331 - Chemistry of the heaviest elements - One atom at a time is an excellent article covering the development and future prospects of atom-at-a-time chemistry of the transuranium elements. 

Hoffinan, Darleane C., and Lee, Diana M. (1999). Chemistry of the Heaviest Elements—One Atom at a Time." Journal of Chemical Education 76(3) 331-347. 

Achievements in the area of the theoretical chemistry of the heaviest elements are overviewed. The influence of relativistic effects on properties of the heaviest elements is elucidated. An emphasis is put on the predictive power of theoretical investigations with respect to the outcome of "one-atom-at-a-time" chemical experiments. 

Of the transactinide elements, only the chemistry of rutherfordium and hahnium has been studied. These elements all have short half-lives and study of their chemical properties must occur at the accelerators where they are produced. Since typical production rates are such that the elements are produced one-atom-at-a-time, the experiments to deduce the chemistry of these elements must be carried out many times... 

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