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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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La 0.00 0.00 -
Ce 2^5/2 2.54 2.56 -
Pr 3H, 3.58 3.62 3.47
Nd 4^e/2 3.62 3.68 3.52
Pm bh 2.68 2.83 —
Sm *Hbl2 0.84 1.55 1.58
Eu 7F0 0.00 3.40 3.45
Gd 8^7І2 7.94 7.94 7.9
Tb 7Fe 9.7 9.7 9.6
Dy 6^15/2 10.6 10.6 10.3
Ho bh 10.6 10.6 10.4
Er 4Aö/2 9.6 9.6 9.4
Tm 7.6 7.6 7.0
Yb *F7/2 4.5 4.5 4.3
Lu 0.00 0.00 -
N 2 {[02 ß* J(J + 1)/3*'Z’] + a } *a.J + l)e EjltT
x = —- (14)
2 (2 J + 1)
where N is the Avogadro number, k the Boltzmann constant, T the absolute temperature, ß the Bohr magneton and g the Land6 splitting factor and is given by
g = 1 -F [S(S + 1) + J(J + 1 )-L(L + 1)]/2J(J + 1)
The symbols S, L, and J are the quantum numbers (p. 101) of the 4/ electron shell. The quantities Ej s are the energy levels of the ions with respect to the ground state. The factor a is given by
Fj+i Fj
ß2
a =
EJ+1 — Ej Ej — Ej-i
6(2J + 1) where
Fj = 1/J [(S + L+ 1)2-J2] [J2_(S-L)2]
The explicit form of eq. 14 in the case of Eu3+ is given by Van Vleck [207] as
yEu = ^mol
0.1241
xT
24+(13.5ж-1.5)е-*+(67.5ж-2.5)е-3*+(189а;-3.б)е-в*+...
1 + 3e-*-f 6e-3*+7e-e*+ ...
(15)
Conductivity, Transference Number, and Activity Coefficient 37
where x is 1/21 of the ratio of the overall multiplet width of the 7F term (in ergs) to kT. The multiplet width of the 7F term of Eu3+ is ~5022 cm-1 (1 cm-1 = 1.986 x 10-16 ergs).
The readers will undoubtedly agree that the elucidations and derivations of the equations 13—15 are beyond the scope of this book, but chemists with some physical inclination may find some satisfaction in reading through Van Vleck’s [207] “Theory of Electric and Magnetic Susceptibilities” to quench their mathemetical thirst. Instead of tabulating the measured magnetic moments of all europium compounds with variations we will mention the magnetic behaviour of the individual compounds as we deal with them.
Conductivity, Transference Number, and Activity Coefficient
In dilute solution the rare earth salts behave as 1:3 electrolytes and obey the Onsager equation in a modified form up to a concentration of 0.01 N. The behaviour of various rare earth salts, such as chlorides, bromides, nitrates and perchlorates has been examined [209—212]. The equivalent conductivity data for the rare earths is compiled in Table 11. Extensive ion-pair formation has been observed for rare earth sulphate solutions.
Table 11. Equivalent conductivities of the rare earths at 25° C
M3+ ^0 M3+ ^0
La 69.6 Dy 67.4
Ce 69.8 Ho 66.3
Pr 69.5 Er 65.9
Nd 69.6 Tm 65.4
Sm 68.6 Yb 65.4
Eu 67.8 Lu 64.7
Gd 67.4 Y 64.8
The cation transference numbers of various rare earth salts have been measured. Speddlng et al. [213] made an extensive study of the chloride system in aqueous solution and determined the transference numbers for La, Ce, Pr, Nd, Sm, Eu, Er and Yb over a wide range of concentrations. The transference numbers of La, Ce, Pr, Nd and Sm are approximately the same, whilst a decrease with increasing atomic number is observed beyond Sm. A plot of transference number against the square root of the concentration is found to be linear within the range 0.007 to 0.1 N. However, the slopes of the lines do not agree with the Onsager limiting values. The data of Spedding et al. [213] for EuCk in various concentration ranges are reproduced in Table 12.
38
Preparation and Properties of Europium
Table 12. Cation transference numbers of aqueous solutions of EuCls in various concentration ranges at 25° C
Concentration Exptl. uncorrected Corrected* trans. {N) Trans. No. No.
0.1056 0.4357 0.4353
0.09198 0.4375 0.4371
0.07665 0.4404 0.4401
0.07539 0.4417 0.4414
0.04599 0.4484 0.4484
0.03016 0.4520 0.4520
0.01533 0.4585 0.4586
0.01056 0.4605 0.4607
0.00766 0.4620 0.4624
* Values obtained by using volume and solvent correction factors (see L. G. Longsworth and D. A. MacInnes: Chem. Rev. 11, 171 (1932)).
The activity coefficients (y±) of aqueous solutions of EuCls (Table 13) and other rare earths have been measured by Speddestg et al. [214]. The values of Table 12 were used to calculate the activity coefficients. The
Table 13. Activity coefficients of EuCls solutions at 25° C
,, . -r, , ,T v Mean molal activity
Molality E.M.F (mV.) coeff. (y±)
0.03532 0.000 0.4159
0.02522 3.850 0.4506
0.01008 14.798 0.5513
0.00504 23.558 0.6290
0.00353 28.225 0.6679
0.00252 32.725 0.7035
0.00101 45.502 0.7864
data agree well with the Debye-Huckel theory showing only a minor deviation at 0.1 N.
Electronegativity
Pauling [215], on purely empirical grounds, first introduced the term electronegativity to define that qualitative property of an atom in a molecule to “attract electron[s] to itself”. The property of electronegativity of an atom is different from the electrode potential of the element. Nowadays there are various methods for measuring electronegativity of an atom (xa) in a qualitative manner. Among the large number of electronegativity scales in existence, the one due to Mulliken216 has a great
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