Europium general properties

Europium and ytterbium di-valence. The oxidation state II for Eu and Yb has already been considered when discussing the properties of a number of divalent metals (Ca, Sr, Ba in 5.4). This topic was put forward again here in order to give a more complete presentation of the lanthanide properties. The sum of the first three ionization enthalpies is relatively small the lanthanide metals are highly electropositive elements. They generally and easily form in solid oxides, complexes, etc., Ln+3 ions. Different ions may be formed by a few lanthanides such as Ce+4, Sm+2, Eu+2, Yb+2. According to Cotton and Wilkinson (1988) the existence of different oxidation states should be interpreted by considering the ionization... 

A book (775) by Sinha about rare earth complexes in general, and another book (775) about europium, illustrate well the two main epochs through which the interest in lanthanides has passed. For the chemist, it is useful to have a smoothly var5ung series from La(III) to Lu(III) in which Y(III) is inserted between Dy(III) and Ho(III), where the chemical properties essentially vary as a function of the ionic radius, and it is also interesting to study the exceptional deviations in direction of M(IV) or M(II). The chemists early developed a devotion to half-filled shells which is now explained by interelectronic repulsion in the partly filled shell, and which got its quantitative expression as spin-pairing energy. For the spectroscopist, each M(III) is interesting as an individual, and... 

Here, the so-called heavy lanthanides include the elements from samarium to-lutetium, except for ytterbium and europium which behave like bivalent metals and have unique properties. For these heavy-lanthanide-carbon systems, no complete phase diagram was found, only some information about the formation and the crystal structure of the carbides is available. On the basis of these data the general characteristics of the phase diagrams of the heavy-rare-earth-carbon systems can be summarized. In this case the yttrium-carbon phase diagram may be regarded as the best prototype available for compounds of the heavy lanthanide systems with carbon. 

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