Oxidation States of Actinoids

Like the lanthanoids, the single most common oxidation state shown across the actinoid series is +3. However, the actinoid series as a whole shows FAR greater variability in accessible oxidation states than the lanthanoid series does -- in addition to the common +3 baseline, individual actinoids are also found showing +2, +4, +5, +6 and even +7 oxidation states, a considerably wider spread than the lanthanoids' more limited +2/+3/+4 range (section 4.5.3), and a direct consequence of the closer energy spacing between the 5f, 6d and 7s orbitals already discussed in section 4.5.5.1.

Specific worked examples illustrate this wider spread. Two elements, americium (Am) and thorium (Th), are noted as showing the LOW +2 oxidation state in certain compounds -- for example, thorium iodide, ThI₂, is a genuine (if unusual) example of thorium adopting the +2 state, well below its more typical +4. At the other end of the range, the elements thorium, protactinium, uranium, neptunium, plutonium and americium (Th, Pa, U, Np, Pu, Am) are collectively noted as showing the HIGH +5 oxidation state under suitable conditions. And at the very top of the accessible range, neptunium and plutonium (Np and Pu) specifically are noted as capable of reaching the exceptionally high +7 oxidation state -- the highest oxidation state reached anywhere within the actinoid series, and indeed among the highest oxidation states found anywhere in the periodic table outside of a handful of specialised high-valent transition-metal oxo/fluoro compounds. This dramatically wider oxidation-state range, spanning from +2 up to +7 across different actinoids (and, in a few cases, even within the accessible range of a SINGLE actinoid such as n …