Chemical properties 

Different from the 4f orbitals in the lanthanides, the 5f orbitals within the earlier actinide elements are more extended and so can be occupied in chemical bonding. This directs to a pattern of chemistry more similar to that found in the d block, with the opportunity of variable oxidation states up to the maximum probable determined through the number of valence electrons. Most thorium compounds consist of Th^IV (example ThO₂) and with uranium the states from +3 to +6 can be created. UO₂ is often nonstoichiometric, and the natural mineral U₃O₈ possibly consists of U^IV and U^VI. Uranium hexafluoride is created industrially by using ClF₃ like a fluorinating agent:

Being unpredictable, it is employed to separate the isotopes ²³⁵U and ²³⁸U for nuclear fuel applications. Several other U^VI compounds consist of the uranyl ion UO²⁺₂a linear unit along with bonding involving both 5f and 6d orbitals: instances involve the mineral carnotite and Cs₂[UO₂Cl₄] in which uranyl is complexed to four chloride ions.

In the series the maximum attainable oxidation state is +7, within the mixed oxides Li₅AnO₆ (An=Np, Pu). High oxidation states become more strongly oxidizing with increasing atomic number, like in the d block. This tendency is demonstrated in Fig. 1. That depicts a Frost diagram with the oxidation states of a number of actinides that are found in aqueous solution. The oxocations AnO⁺₂and AnO²⁺₂ are feature for An^V and An^VI with An=U, Np, Pu and Am, except the slopes of the lines in the figure depict their progressively more strong oxidizing character. Complex solution equilibria are feasible: with Pu, for instance, all states from +3 to +6 can be exists simultaneously. The dissimilar redox stability of U and Pu is significant in nuclear fuel reprocessing, one function of that is to separate not used uranium from

Fig. 1. Frost diagram showing the oxidation states of some actinides in aqueous solution at pH=0.

²³⁹Pu that is itself used like a nuclear fuel. Dissolving the used up fuel elements in aqueous HNO₃ gives Pu^IV and U^VI. Consequent separation steps then rely on variations in complexing power and solubility of these ions.

The organometallic chemistry is very much less wide than that of the d block, and different from that of the lanthanides through virtue of the large sizes of the early actinides and their wide variety of accessible oxidation states. Uranium has been very much investigated than other elements. Usual compounds involve the cyclopentadienyl (Cp=η⁵-C₅H₅) compounds [AnCp₃], [AnCp₄] and mixed Cp-halides like [AnCp₃Cl]. Mainly interesting is the sandwich compound [U(η⁸-C₈H₈)₂] along with two planar cyclooctatetraene rings termed as uranocene; analogs are created with neighboring actinides. Even though formally they can be considered like compounds of An⁴⁺ with the aromatic 10 π electron ring [C₈H₈]^2- there is a few covalent bonding that is involving actinide 5f and 6d orbitals.

Later actinides depict a more restricted range of oxidation states, and are more identical to the lanthanides. The +4 state is observe in AnO₂ and AnF₄ so far as Cf. It becomes increasingly more oxidizing for later elements, although with a break at Bk⁴⁺ (that is more easily created than Cm⁴⁺ or Cf⁴⁺) following the half-filled 5f shell and so analogous

to the happening of Tb⁴⁺ in the lanthanides. From Am to Md the +3 state is mainly stable in aqueous solution and solid compounds. Though, near the end of the series the +2 state shows more stable than in the lanthanides and is the usual one for No. This variation must reflect a dissimilar balance of ionization energies and lattice or solvation energies, although the data needed to comprehend it in detail are not available. With only some atoms presented and along with extremely short half-lives, chemical investigations of afterwards actinides rely on tracer methods by using a stable element of supposed similar chemical behavior to act like a carrier. For instance, the existence of No²⁺ can be inferred from its precipitation (and subsequent detection through its radioactivity) with Ba²⁺ as BaSO₄ under circumstances in which other oxidation states form soluble compounds.