The fourteen elements following actinium ,i.e., from thorium (Th) to lawrentium (Lr) are called actinoids. Unlike the lanthanoids, all the actinoids are radioactive and most of them have short half lives. Only thorium and uranium(U) occur in significant amount in nature and a trace amounts of Plutonium(Pu) is also found in Uranium ores.Neptunium(Np) and successive heavier elements are produced synthetically by the artificial transformation of naturally occuring elements by nuclear reactions.
Similar to lanthanoids, they are placed at the bottom of the periodic table.
The electronic configuration of actinoids is not definite. The general valence shell electronic configuration of 5f elements is represented as [Rn]5f 2 −14 6d0 −2 7s2 . The following table show the electronic configuration of actinoids.
Table : electronic configuration of actinoids
Like lanthanoids, the most common state of actinoids is +3. In addition to that actinoids show variable oxidation states such as +2 , +3 , +4 ,+5,+6 and +7.
The elements Americium(Am) and Thorium (Th) show +2 oxidation state in some compounds , for example thorium iodide (ThI2). The elements Th , Pa, U ,Np , Pu and Am show +5 oxidation states. Np and Pu exhibit +7 oxidation state.