Actinium oxidation state

The metallic ion of actinium has an oxidation state of +3. Two examples of Ac compounds follow ... 

The high oxidation states of metal ions occurring at the beginning of the transition and actinium series usually are found in complex oxycations of the types MO + and M0 +. The remarkable... 

Actinium forms halides only in the (+3) oxidation state, AcXs and AcOX (X = F, Cl, Br). The trihalides have the LaFs (X = F) and UCI3 (X = Cl, Br) structures, respectively. 

Table 24.2 Oxidation states of actinium and the actinoids. The most stable states are shown in red.

Little need be said about the halides of actinium. All of the binary halides of this element have been prepared by conventional procedures, and the straightforward, uncomplicated chemical behavior that actinium exhibits generally is also evident here. Thorium, however, presents quite a different problem. Thorium gives no indication of existence in aqueous solution in an oxidation state lower than +4. From considerations of the... 

As early as 1923 N. Bohr suggested that there might exist a group of IS elements at the end of the Periodic Table Uiat would be analogous in their properties to the IS lanthanide ("rare earth") elemrats. This idea, combined with the increasing stability of the -t-3 oxidation state for the transuranium elem ts as the atomic number increases from Z = 93 to 96, led Seaborg to the conclusion that these new elemrats constituted a second rare earth series whose initial member was actinium. As the atomic number increases from 90, electrons are added in the Sf subshell similar to the occupation of the 4f subshell in the lanthanides, see Table 16.1. This series would be terminated with element 103 since this would correspond to the addition of 14 electrons for a completed Sf subshell. 

The chemical properties span a range similar to the representative elements in the first few rows of the periodic table. Francium and radium are certainly characteristic of alkah and alkaline earth elements. Both Fr and Ra have only one oxidation state in chemical comhina-tions and have little tendency to form complexes. Thallium in the 1+ oxidation state has alkah-like properties, but it does form complexes and has extensive chemistry in its 3+ state. Similarly, lead can have alkaline earth characteristics, hut differs from Ra in forming complexes and having a second, 4+, oxidation state. Bismuth and actinium form 3+ ions in solution and are similar to the lanthanides and heavy (Z > 94) actinides. Thorium also has a relatively simple chemistry, with similarities to zirconium and hafiuum. Protactinium is famous for difficult solution chemistry it tends to hydrolyze and deposit on surfaces unless stabilized (e.g., by > 6 M sulfuric acid). The chemistry of uranium as the uranyl ion is fairly simple, hut... 

O Table 18.9 gives oxidation states of actinide elements (Katz et aL 1986). Actinium and transplutonium elements (from Am to Lr) take 3+ as the most stable oxidation state and they behave similar to the lanthanide elements, except element 102, No, which seems to prefer the 2+ state. Because of the itinerancy of the 5f electrons, the lighter actinide elements take broad range of oxidation states. The light transuranium elements, Np, Pu, and Am can behave as 3+ to 7+ cations and the most stable oxidation states of these three elements are 5+, 4+, and 3+, respectively. 

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