<P> The actinide series derives its name from the first element in the series , actinium . The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide . All but one of the actinides are f - block elements , with the exception being either actinium or lawrencium . The series mostly corresponds to the filling of the 5f electron shell , although actinium and thorium lack any f - electrons , and curium and lawrencium have the same number as the preceding element . In comparison with the lanthanides , also mostly f - block elements , the actinides show much more variable valence . They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties . While actinium and the late actinides ( from americium onwards ) behave similarly to the lanthanides , the elements thorium , protactinium , and uranium are much more similar to transition metals in their chemistry , with neptunium and plutonium occupying an intermediate position . </P>
<P> The actinide series derives its name from the first element in the series , actinium . The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide . All but one of the actinides are f - block elements , with the exception being either actinium or lawrencium . The series mostly corresponds to the filling of the 5f electron shell , although actinium and thorium lack any f - electrons , and curium and lawrencium have the same number as the preceding element . In comparison with the lanthanides , also mostly f - block elements , the actinides show much more variable valence . They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties . While actinium and the late actinides ( from americium onwards ) behave similarly to the lanthanides , the elements thorium , protactinium , and uranium are much more similar to transition metals in their chemistry , with neptunium and plutonium occupying an intermediate position . </P>
where are the actinide and lanthanide elements found
where are the actinide and lanthanide elements found
f - block
f - block