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Europium - Sinha S.P.

Sinha S.P. Europium - Springer-Verlag, 1967. - 88 p.
Download (direct link): europium1967.djvu
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798° —m.p. bee 4.13 —
Nd up to 868° hex 3.656 ± 0.0002 11.798 ± 0.002
868° —m.p. bcc 4.13 —
Sm up t-o 917° rhom 8.996 a = 23° 13'
bcc 4.07 —
Eu up to m.p. bcc 4.5820 ± 0.0004 —
Gd up to 1262° hep 3.6360 ± 0.0009 5.7826 ± 0.0006
1262° — m.p. bcc (?) 4.06 —
Tb up to 1310° hep 3.6010 ± 0.0003 5.6936 ± 0.0002
Dy up to 950° hep 3.5903 ± 0.0001 5.6475 ± 0.0002
Ho up to 966° hep 3.5773 ± 0.0001 5.6158 ± 0.0002
Er up to 917° hep 3.5588 ± 0.0003 5.5874 ± 0.0003
Tm up to 1004° hep 3.5375 ± 0.0001 5.5546 ± 0.0004
Yb up to 798° fee 5.4862 ± 0.0004 —
798° — m.p. bcc 4.45 —
Lu up to 1400° hep 3.5031 ± 0.0004 5.5509 ± 0.0004
Sc r.t. hep 3.3090 ± 0.0001 5.2733 ± 0.0016
fee* 4.541 ± 0.0005 —
Y r.t. to 1490° hep 3.6474 ± 0.0007 5.7306 ± 0.0008
1490° — m.p. bcc 4.11 ± 0.0002 —
* There is some doubt as to whether or not this form exists.
The density (d), atomic volume (at. vol.) and the atomic radius (at. rad.) of europium have been calculated from the lattice constants by Spedding et al. as d = 5.245 g/cc, at. vol. = 28.982 cc/mole and at. rad. = 1.9841 ± 0.0002 A. The densities of the rare earths show a gradual increase through the series with increasing atomic number but there are large deviations for europium and ytterbium. The density of La and Gd were found to be slightly lower than would be expected from the density vs, atomic number plot, whereas the density of Ce is slightly higher. A plot of the values of atomic volumes against atomic numbers (Fig. 7) also shows a large deviation for europium and ytterbium. Euro-
28 Preparation and Properties of Europium
piuin does not really belong to the rare earth series. It has a much lower density than the other rare earths. It belongs more correctly in the calcium-strontium-barium series (see Fig. 7) as is indicated by relatively low melting and boiling points, volatility and action of moisture. The heats of sublimation of europium (42 kcal/mole) and ytterbium (40 kcal/mole) are the lowest in the rare earth series (typically 70—80 kcal/mole) and are comparable in magnitude with the alkaline earths (37 kcal/mole).
La Pr Pm Eu Tb Ho Tm Lu Ba Ce Nd Sm Gd Du Hr Yb Hf
At No. —-
Fig. 7. A plot of atomic volume of the rare earths against atomic number, o atomic volume calculated from lattice constants of the stable structure at room temperature or above, □ atomic volume for bcc structure
In electrical resistivity europium (81 x 10® ohm-cm) resembles the isostructural barium (60 X 106 ohm-cm) [175]. Ytterbium has the lowest resistivity in the rare earth series (27 X 106 ohm-cm).
Atomic Structure, Atomic Radius, and Ionic Radius 29
Atomic Structure, Atomic Radius, and Ionic Radius
A quick look in the periodic table reveals that the rare earths in a very unsophisticated way are grouped together with the members of group III b. In the conventional long form of the periodic table La is classified with Sc and Y. A number of writers [176,177] have questioned this classification and are more inclined to include Lu (instead of La) in the same column as Sc and Y. There are logical arguments in support of each of these points of view. Here we have no intention to evaluate the relative merits of these arguments.
Following Xe (Z = 54; Is2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d6 5s2 5pG) comes Cs (Z = 55) in which the first electron is added to the 6«s level, and in Ba (Z = 56) the 6s level is completely filled (Xe-core + 6s2). The next electron in La {Z = 57) goes to the 5d level giving an electronic configuration Xe-core -f- Sd1 6s2. The first 4/ electron is seen in Ce (Z = 58: Xe-core + 4/1 5d1 6s2). Pr (Z = 59) instead of having the electronic configuration Xe-core -(- 4/2 5c/1 6s2 actually has the ground state configuration Xe-core + 4/3 6s2. The 5d electron drops to the 4/ level. Htjnd’s theoretical prediction in 1927 suggests a 4fn 5d16s2 structure for the rare earths (n = 0 to 14 for La to Lu). However, the observed ground state [178—180] configurations rather point, towards a 4/n+1 6s2 configuration (Table 6). The half filled (4/7), and completely
Table 6. Ground state electronic configuration of neutral rare earth atoms
Rare _T „ „ Ground
earths Hund Kxinkenberg Cunningham state
La 4/° 5d1 6 s2 4/0 5d1 6s2 4/° ôd1 6s2 -
Ce 4f1 ôd1 6s2 4/2 6 s2 4/1 ôd1 6s2 ^4
Pr 4/s ôd1 6 s2 4/s 6s2 4/a 6s2 4^9/2
Nd 4/3 5 d1 6 s2 4Z4 6s2 4/* 6a2 5A
Pm 4f* 5 d1 6 s2 4/s 6 s2 4/5 6s2 6^6/2
Sm 4/5 5 d1 6 82 4/6 6 s2 4/* 6a2 7^o
Eu 4/6 5d1 6 82 4V 6s2 4f 6«2 ^7/2
Gd 4f7 5 d1 6 S2 4/7 5d1 6s2 4/7 ôd1 6s2
Tb 4/8 ôd1 6 82 4/9 6 82 4/® 6a2 6-^15/2
4/8 5d1 6 82 4/8 5dx 6s2
Dy 4P ôd1 682 4/10 6S2 4/10 6s2 6*8
4/9 5d1 6 S2
Ho 4/10 ôd1 6 82 4/11 № 4/11 6a2 *-^15/2
4/1° ôd1 6 82
Er 4/11 en & M 6s2 4/12 6*2 4/!2 6s2
4/11 ôd1 6*a
Tm 4/12 ôd1 6 82 4/18 6 s2 4/!8 6a2 2F 7/2
Yb 4/18 ôd1 6s* 4/14 6s2 4/14 6s2
Lu 4/14 ôd1 6s2 4/14 ôd1 6 s2 4/14 ôd1 6a* **>42
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