Grupo 3 Da Tabela Peri³dica
Grupo 3 Da Tabela Peri³dica
Grupo 3 Da Tabela Peri³dica

Grupo 3 Da Tabela Peri³dica

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    The Positions of Lanthanum Actinium] and Lutetium

    Lawrencium] in the Periodic Table

    William B.

    ensen

    University of Wisconsin-Madison. Madison, WI 53706

    The deba te as to whether lanthanum and actinium or lu-

    tetium (and, more recently, lawrencium) should be placed in

    erouo IIIB of the neriodic table alone with scandium and

    vt

    .

    trium (or rquiv:ilintly, in electronic tir rns, which pair ihod d

    he considered as he iirsr memhrrs o ft he d block ior periuds

    6 and 7) has a long, but poorly publicized, history.

    r

    quite

    some time i t has been known tha t yttrium, and, to a lesser

    degree, scandium are closer in their chemical properties to

    lutetium and the other heavy rare earths than they are to

    lanthanum 1,2)and on this basis alone a number of chemists

    in the 1920's and 1930's assigned lutetium rather than lan-

    thanum

    to

    erouo IIIB 3).The current consensus. which olaces

    .

    lanrhanum and actinium in this position instead, appears to

    have evolved during the 194O's a h , : with the u s e d oeriodic

    tahles based on electronic configurk ion and t he concept of

    th e differentiating electron.

    Early spectroscopic work on t he rare earths seemed to in-

    dicate tha t the ground states of their atoms had, with few

    exceptions, an electronic configuration of the form [Noble

    Gas](n

    -

    2)fx-'(n l)d'ns2. Indeed, this was thought to

    conform to the ideal electronic configuration for the f-block

    elements in general

    (2).

    Thus, ytterbium was assigned the

    ground state [Xe]4f135d16s2 nd lutetium the ground sta te

    [Xe]4f145d16s2, esulting in a 4f differentiating electron for

    lutetium and firmly establishing it as the last member of the

    f-block for period 6.Barium, on the other hand, had t he con-

    figuration [Xe]6s2and lanthanum t he configuration [Xe].

    5d16s2, hus giving lanthanum a 5d differentiating electron

    and establishing it in group IIIB as the first member of the d

    block for period 6. This assignment for lanthanum appeared

    to be further justified by the analogy between its configuration

    and the configurations of the other members of group IIIB:

    Sc = [Ar]3d14s2 nd Y = [Kr]4d15s2.

    More recent spectroscopic work, however, has revised the

    earlier electronic configurations 4). Only three of the rare

    earths in period 6 (La, Gd, and Lu) are now known

    to

    have the

    ground sta te [Xe]4p-'5d16s2, all of th e rest having the con-

    figuration [Xe]4fx6s2. n period

    7

    only six of the actinides (Ac,

    Pa, U Np, Cm, and Lr ) have the old configuration. Thorium

    has the configuration [Rn]6d27s2 nd th e remaining eight the

    configuration [Rn]5f*7s2.This strongly suggests [Noble Gas](n

    - 2)fi s2ra ther than [Noble Gas](n )fX-Vn - )dlns2 as

    th e ideal ground sta te configuration for th e f-block elements

    in general. Ytterbium and nobelium now have the configu-

    Revised version

    of the currently popular

    medium length

    block

    form

    of

    the periadictable.

    634

    Journal

    of

    Chemical Education

  • 7/27/2019 Grupo 3 Da Tabela Peridica

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    ration [Nohle Gas](n Z)P4ns2and lutetium and lawrencium

    the configuration [Nohle Gas](n 2)f14(n )d1ns2, esulting

    in a d rather than an f differentiating electron for both lute-

    tium and lawrencium and makine them eouallv valid candi-

    .

    dnws for the first memhers of the d block in periods t and 7

    On the other hand. the IRn16d27s%onfirurati tn or thorium.

    which no one doubts is'au )-block element with an irregula;

    configuration, strongly sul,pc,rts the supposition that both

    lanthanum and actinium should be cons~dered s f-t ~lo ck

    I

    ements with irregular configurations derived from the ideal

    configuration [Nohle Gas](n 2)f1ns2. In other words, lan-

    thanum and actinium should be considered the first memhen

    of the f hlock (rather than Ce and Th),ytterbium and nohel-

    Atomic

    Radiis

    A l

    1.

    Periodlc Trends

    in

    Various

    P

    Sum

    of

    the First

    TWOonization

    POtentiaI~*

    eV)

    1 9 z \ y

    1 8 6 1 1 ~

    17 04

    versus

    ium should he considered t1.e last members of the f hlock

    (rather than Lu and Lr), and lutetium and lawrencium (rather

    than La and Ac) shouldbe considered the first memhen of the

    d hlock in periods

    6

    and 7 and assigned t o Group IIIB along

    with scandium and yttrium.

    The argument that the total (i.e., core plus valence) elec-

    tronic configurations of lanthanum and actinium are closer

    to those of scandium and vtt rium than are the confieurations

    of lutetium and l a w r e n c h (due to their filled (n 2)f'4

    suhshells) is misleadins. One must consider intraoeriod

    as

    well

    as intragroup analog&. Thus, the remaining kine d-block

    elements of period

    6

    (Hf Hg) all have the complete [Xe]4f14

    core like lutetium and not just the [Xe] core of lanthanum.

    lrtles tor the First Part

    of

    the d-BI(

    Melting

    ointb

    (OK)

    F m m

    ef. I). Data om ref. (f8)

    Volume

    59

    Number

    8

    August

    1982

    635

  • 7/27/2019 Grupo 3 Da Tabela Peridica

    3/3

    Likewise, in oassine down the columns of the

    d

    hlock from

    Table 2 A Comparlson 1 Vartous Prowrttes of Sc and Y versus

    Ti-Z n one alk av s t: ,uniers the addition of the 4f1'su bshe ll

    on passinr from period o period 6. In sho rt, if on e wishes to

    usi analogies hased on trehd s in th e configurations of the

    cores, eighteen of the se analogies favor th e assignment of lu-

    tetium an d lawrencium to G roup IIIB an d only one favors the

    assignment of lanthan um an d actinium.

    Areuments of this nature were nu t forward hv Lu der in

    favor of the reassignmellt of lutetium and lawrencium over

    a dec ade ago bu t app ear to have gone unno ticed (5,151. Like-

    wise, the Russian che mist Christyakov, using periodic trend s

    in ionization potentials and atomic radii, arrived a t he same

    conclusion

    f a ) .

    One may also ad d

    to

    this list trends in ionic

    radii, redox poten tials, and electronegatives,

    as

    well as the

    chemical hehavior of scandium a nd y ttrium mentioned earlier.

    Th e most compelling evidence, however, has heen presen ted

    by the physicis ts ( s 1 3 ). Th is includes comparisons of tren ds

    in the melting points of the elem ents (1 1,J 2) , their crystal

    s t ructures at room temoe rature 11). he crvstal s t ructures

    of their oxides and various intermktaiiic compounds ( l l ) , he

    structu res of their excited state soectra (11 ).their suoercon-

    ductivit ies (10, 11), and th e s t r uku res of t'heir c ond kt iv i ty

    hands as revealed by X-ray isochromats (13). All of these

    properties unanimously favor the plac ement of lutetium and

    lawrencium, rather than lanthanum and act inium, in group

    IIIB. Some example data a re summarized in Tables

    1

    an d

    L

    In fac t, so overwhelming is the evidence for this assignmen t

    that Mazurs adopted i t in the

    1974

    edition of his classic

    monoe ranh on th e oeriodic tahle (14). However. a auick ex-

    aminat ion of over gfteen freshman chemistry te kt s in d four

    popular inorganic texts published since 1975 revealed that

    none of them h ad revised their periodic tables 15). ndeed,

    in talking with his fellow chemists, the auth or discovered tha t

    none of the m was aware of th e evidence favoring th e reas-

    signment of lutetium and lawrencium or indeed that there

    ever was any que stion abou t their placements (a category in

    which the a uthor mus t include himself until very recently).

    As chemists, the periodic tahle is presumed to he-our special

    province; surely its about time we pay atten tion to w hat the

    physicists have to

    tell us ahout its arrangement. A revised

    version of the currently popular medium-length hlock form

    of the table is shown above.

    Literature Cited

    -. . ..

    New York. 1961. Chap. 2

    (3)

    See,

    forexampie, Shemyskin,

    F.

    M.,Zh. Obshch. Khim.2.62 11932) andHury, C.R.,

    J. Amer Chem Soc. 43,1602 (1921). Further examples can he found n reference

    114).

    ~ ~~~

    thore 1 Lu and La

    Propew

    Highest common

    oxidation state

    Precipitation of sulfate

    in fractional

    crystallization'

    Stlllcture of metal

    at r m m

    temperatureb

    Shlc ture of oxide

    (M20s) '

    Y group Y group

    Y

    group

    Ce

    group

    special

    hCP hCP hc p double hc p

    :[AB~,.]C

    NIcS ~ A B ~ ~ ~ I Cpecial

    hex. CN-7

    A-MIOO

    Presence of low-lying No

    NO

    No

    Yes

    nonhydrogenic

    I-orbitals

    &Block-like structure Yes Yes Yes NO

    for

    conduction

    bandd

    Super~onduc t iv i t y~~~ NO

    No

    No Yes (4.gK)

    Ref.

    (1)

    el. (17)

    ORel. (11)

    'Ref. (13)

    ~ I . 14

    '

    M s ~t r c hk l n ig g l l a d i~ t i o nm u l a s

    (1968). His

    count

    far the lanthanides, however.b ifferswith eg rd o Ce fmh