The actinoids are radioactive elements and the earlier members haverelatively long half-lives, the latter ones have half-life values ranging from a day to 3 minutes for lawrencium (Z = 103). The latter members couldbe prepared only in nanogram quantities. These facts render their studymore difficult.
There is a greater range of oxidation states, which is attributed to the fact thatthe 5f, 6d and 7s levels are of comparable energies. The actinoids show ingeneral +3 oxidation state. The elements, in the first half of the series frequentlyexhibit higher oxidation states. For example, the maximum oxidation stateincreases from +4 in Th to +5, +6 and +7 respectively in Pa, U and Np butdecreases in succeeding elements. The actinoids resemble the lanthanoids inhaving more compounds in +3 state than in the +4 state. However, +3 and +4ions tend to hydrolyse. Because the distribution of oxidation states amongthe actinoids is so uneven and so different for the earlier and latter elements.It is unsatisfactory to review their chemistry in terms of oxidation states.