Determination of oxidation potential of the pair Fm2+/Fm3+

Lanthanides / Actinides / Redox properties / Hydration / CovalenceSummary. The existence of low oxidation states of lanthanides and actinides in aqueous solution has been reexamined in the light of recent data. The retained redox data corresponding to the 3 + /2+ couples are given, and earlier reports of the existence of monovalent mendelevium is not confirmed. By comparing divalent, trivalent and tetravalent ions, the effective charges of the lanthanide and actinide ions have been quantified. It is shown, based on experimental EXAFS data, and modelling of the aquo ions, that the covalent effect in these series increases with the oxidation state, is larger for actinides than for lanthanides and maximum for trivalent and tetravalent ions at the beginning of the series and, in each case, becoming negligible around the middle of the series. For divalent ions this covalent effect is small and constant through the series. Characteristics of the ions have been evaluated and hydration properties deduced.

Section: Existence Of Low Oxidation States Of Lanthanides and Actinidmentioning

confidence: 99%

About low oxidation states, hydration and covalence properties of f elements

David¹

2008

“…But its direct production by Cm(III) oxidation is difficult due to the high potential of the Cm(IV)/Cm(III) pair [151,152]. The stability of +2 state of oxidation on the whole increases with rising TPE atomic number [151], and the Fm(III)/Fm(II) pair has the same oxidation potential as the Yb(III)/Yb(II) pair [153], It has been shown [154] that Fm(III) can be reduced to Fm(II) by electrolysis on mercury cathode.…”

Section: Isotopes and Their Propertiesmentioning

confidence: 99%

Recent Analytical Chemistry of the Transplutonium Elements

Myasoedov¹

1983

The modern state of the analytical chemistry of the transplutonium elements (TPE) ranging from Americium to Lawrencium are reviewed. The main characteristics of the most important isotopes are given, and properties of metals and oxides are discussed. Special attention is paid to the TPE properties in unusual oxidation states in solutions, the methods of production and stabilization, and current methods of isolating and separating of these elements. In conclusion the principal methods of determining TPE and impurities in them are considered.

“…The results for Fm may be expressed as follows: to -1.55 V relative to the standard Pt, H 2 ¡ H + electrode. Later work [74] by these scientists narrowed the range to between -0.64 and -1.15V and, most recently, they were able to estimate the potential was the same as the Yb 3+ Yb 2 + couple within 0.02 V, or -1.15 V [75,76], This estimate was based on measuring the ratio of Fm(III) to Fm(II) during the cocrystallization of Fm(II) with SrCl 2 while changing the ratio of Yb(II)/Yb(III) in each experiment. The difference between the standard potentials of Fm and Yb is then easily determined from the Nernst equation.…”

Section: Few Atom Chemistrymentioning

confidence: 99%

Chemistry of the Elements Einsteinium through Element-105

Hulet

1983

All known chemical properties of each of the elements 99 (Es) through 105 are reviewed and these properties are correlated with the electronic structure expected for 5/and 6 d elements. A major feature of the heavier actinides, which differentiates them from the comparable lanthanides, is the increasing stability of the divalent oxidation state with increasing atomic number. The divalent oxidation state first becomes observable in the anhydrous halides of californium and increases in stability through the series to nobelium, where this valency becomes predominant in aqueous solution. In this range of elements, the II -<· III oxidation potential decreases from ~ +1.5 to -1.5 volts. These observations lead to the conclusion that, in comparison with the analogous 4/electrons, the 5/ electrons in the latter part of the series are more tightly bound. Thus, there is a lowering of the 5/energy levels with respect to the Fermi level as the atomic number increases.The metallic state of the heavier actinides has not been investigated except from the viewpoint of the relative volatility among members of the series. In aqueous solutions, ions of these elements behave as "normal" trivalent actinides and lanthanides (except for nobelium). Their ionic radii decrease with increasing nuclear charge which is moderated because of increased screening of the outer 6 ρ electrons by the 5/electrons. These relative ionic radii have been obtained from comparisons of the elution position in chromatographic separations.Lawrencium (Lr) completes the actinide series of elements with an electronic configuration of 5 / 14 7 s J 7 p. From Mendeleev's periodicity and Dirac-Fock calculations, the next group of elements is expected to be a ¿/-transition series corresponding to the elements Hf through Hg. The chemical properties of elements 104 and 105 only have been studied and they indeed appear to show the properties expected of eka-Hf and eka-Ta. However, their nuclear lifetimes are so short and so few atoms can be produced that a rich variety of chemical information is probably unobtainable.