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7.1: Lanthanoids

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    The fifteen elements shown in Table \(\PageIndex{1}\) from lanthanum, La (4f0), to lutetium, Lu (4f14), are lanthanoids. Ln may be used as a general symbol for the lanthanoid elements. Although lanthanoids, scandium, Sc, and yttrium, Y, are sometimes called rare earth elements, they are relatively abundant in the earth’s crust. With the exception of promethium, Pm, which does form a stable isotope, even the least abundant thulium, Tm, and lutetium, Lu, are as abundant as iodine. Because lanthanoids have very similar properties and are difficult to separate from one another, they were not useful for basic research and application, and hence they were regarded as rare elements. Since a liquid-liquid solvent extraction method using tributylphosphine oxide became available in the 1960s, lanthanoid elements have been readily available and widely used not only for chemical research but also as materials in alloys, catalysts, lasers, cathode-ray tubes, etc.

    Exercise \(\PageIndex{1}\)

    What is the difference between lanthanoids and lanthanides?


    Fifteen elements La-Lu are lanthanoids and fourteen elements Ce-Lu without lanthanum are lanthanides (meaning the elements similar to lanthanum). Occasionally the names are confused and 15 elements including lanthanum may be called lanthanides.

    Table \(\PageIndex{1}\) Properties of lanthanoids
    Atomic number Name Symbol Electron configuration M3+ radius (pm)
    57 Lanthanum La 5d16s2 116
    58 Cerium Ce 4f15d16s2 114
    59 Praseodymium Pr 4f36s2 113
    60 Neodymium Nd 4f46s2 111
    61 Promethium Pm 4f56s2 109
    62 Samarium Sm 4f66s2 108
    63 Europium Eu 4f76s2 107
    64 Gadolinium Ge 4f75d16s2 105
    65 Terbium Tb 4f96s2 104
    66 Dysprosium Dy 4f106s2 103
    67 Holmium Ho 4f116s2 102
    68 Erbium Er 4f126s2 100
    69 Thurium Tm 4f136s2 99
    70 Ytterbium Yb 4f146s2 99
    71 Lutetium Lu 4f145d16s2 98

    Because the three stages of ionization enthalpy of lanthanoid elements are comparative low, they are positive elements and readily assume trivalent ionic states. Most compounds of lanthano other than Ce4+ (4f0), Eu2+ (4f7), Yb2+ (4f14), are usually Ln3+ ones. Ln3+ species are hard acids, and since f electrons are buried deeply and not used for bonding, they are hardly influenced by ligands. There is a tendency for atomic and ionic radii to decrease with the increase of the atomic number, and this phenomenon is called the lanthanide contraction. This contraction is due to small shielding effects of 4 f electrons, which causes the atomic nucleus to draw outer shell electrons strongly with an increase of atomic number.

    Complexes of lanthanoid metals are 6 to 12 coordinate and especially many 8 and 9 coordinate compounds are known. Organometallic compounds with cyclopentadienyl ligands of the types \(\ce{Cp3Ln}\) or \(\ce{Cp2LnX}\) are also known, all of which are very reactive to oxygen or water.

    This page titled 7.1: Lanthanoids is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Taro Saito via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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