Cesium 137 dating wiki

However, scandium still shows many differences from lutetium because it is even smaller, and in any case the similarity of yttrium is more generally to all of the late lanthanides from gadolinium onward, especially holmium which has almost the same ionic radius.The trends going down from scandium and yttrium to lanthanum tend to be more similar to those going down groups 1 and 2 in the periodic table, while those going down from scandium and yttrium to lutetium tend to be more similar to those in the early transition metals.This phenomenon, based on the poor shielding of nuclear charge by the 4f electrons that are added across the lanthanide series, results in a decrease of ionic and atomic radii across the lanthanide series, causing the early period 6 transition metals (just after the lanthanides) until about rhenium to be very similar to their period 5 homologs.This same effect makes yttrium more similar to lutetium ([Xe]4f) than lanthanum.

Among the lanthanides, lanthanum is exceptional as it does not have any 4f electrons; indeed, the sudden contraction and lowering of energy of the 4f orbital that is important for the chemistry of the lanthanides only begins to happen at cerium.It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype.It is also sometimes considered the first element of the 6th-period transition metals and is traditionally counted among the rare earth elements. Lanthanum has no biological role in humans but is essential to some bacteria.Traditionally, from the 1940s, lanthanum has been placed under scandium and yttrium in group 3 of the periodic table, as its differentiating electron from the previous element goes into a d-orbital.This results in a consistent set of electron configurations in group 3 (Sc: [Ar]3d).

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