ORBITAL ELECTROSEGATIVITIES OF SEUTEAL ATOMS
July, 1963
increase the apparent activation energy. The radioactive catalysts remain inferior. Miscellaneous Experiments.-One of the most interesting observations reported in the literature of the effect of S35on these catalysts was a decrease of catalytic activity as the radioactivity d e ~ a y e d . ~This appeared to be powerful evidence that the reported enhancements of catalytic activity depended on the rate of emission of @-particlesby the catalyst during use. However, studies were apparently not made of the behavior of the non-radioactive catalysts after similar storage times. To clarify this point, the catalytic activities of a radioactive and non-radioactive catalyst were redetermined after storage times up to 227 days. It was found that the catalytic activity decreased linearly with time in both cases and that radioactive and non-radioactive catalysts lost the same fraction of their steadystate activity in the same period of time as shown in Fig. 6. Since the effect is linear with time over the period studied, it is obvious from the radioactive decay law that the decrease of the catalytic activity of the radioactive catalyst is also linearly related to the logarithm of the specific radioactivity. However, since the non-radioactive catalyst showed similar behavior, the effect must be a property of the catalyst not dependent on radiation. In another group of experiments, the problems which arise in trying to duplicate catalyst surfaces for comparative purposes were circumvented by directing Xrays generated a t 180 and 300 kv. on the catalyst bed while the dehydration reaction was pr0ceeding.l' The dose rates of 123 and 113 rad/min., respectively, were comparable to those from the SS5in the radioactive catalysts. No effecis were found, in agreement with (11) N. A. Krohn and H. A. Smith, J . P h p . Chem., 65, 1919 (1961).
1501
previous Russian work utilizing an 800-kev. electron beam.' Preirradiation with Gos0 y-rays to 10" ergs/g. was also without effect. Conclusions From the results of these experiments, it is concluded that the reported enhancements of catalytic activity in the dehydration of cyclohexanol by the addition of radioactive sulfur to the sulfate catalysts are erroneous because comparisons were apparently made on the basis of unit weight rather than unit surface area. When compared on the latter basis, the radioactive materials were found to be less active catalytically than non-radioactive catalysts of the same composition. I n general, for a given set of preparative conditions, the radioactive catalysts have larger surface areas than their nonradioactive counterparts, and this was not apparently considered in the previous work. It is also concluded that since both the non-radioactive and radioactive materials lose catalytic activity with storage time this phenomenon is not related to the decay of the radioactivity, but is a property of the catalyst surface. Thus, the emission of @-particlesfrom the catalyst during the time the dehydration reaction is taking place is of no consequence. This conclusion is supported by the fact that irradiation of the catalyst with X-rays or electrons while the reaction was proceeding had no effect. Acknowledgments.-The authors are indebted to many members of the ORNL staff, especially to W. R. Laing, G. S. Brown, J. S. Eldridge, and R.T . Sherman of the Analytical Chemistry Division and to R. G. Wymer and D. M. Helton of the Chemical Techno1o.y Division for their assistance in carrying out this program. Also of assistance were P. G. Dake and E. A. Woy of the Oak Ridge Gaseous Diffusion Plant.
ELECTRONE(GATIV1TY. IV. ORBITAL ELECTROKEGATIVITIES OF THE NEUTRAL ATOMS OF THE PERIODS T H R E E A AND FOUR A AND OF POSITIT'E IONS OF PERIODS ONE AND TWO1 BY JURGEN H I K Z EAXD ~ H. H. J A F F ~ Department of Chemistry, University of Cincinnati, Cincinnati ,91, Ohio Received January 10, 1963 The orbital electronegativities of the neutral atoms of the A elements of rows three and four and of the monopositive ions of periods one and two are reported and briefly discussed.
Introduction In the preceding a,rticles of this series,I electronegativity has been discussed, based on Mulliken's theoretically well justified3,4definition5
x
I,
=
+ E,2
(1)
This discussion leads to the conclusion that electro(1) (a) J. Hinse and H. H. JaffB, J . Am. Chem. Soc., 84, 540 (1962); (b) J. Hinze, M. A. Whitehead, a n d H . H. Jaff6, ibid., 85, 148 (1963); ( e ) J. Hinae and H. H. JaffB, Can. J . Chem., 41, 1315 (1963). (2) Department of Chemiaitry, Rice Univ., Houston 1, Texas. (3) R . S.Mulliken, J. (?him. Phya., 46, 497 (1949). (4) W.Moffitt, Proe. Roy. SOC.(London), 81102, 548 (1950). L6) R3 S . Mullikenl J , Cham, P h y s , , a, 782 (1934) I
negativity is the property not of an atom, but of an orbital of an atom in a molecule. The electronegativities computed in the light of these considerations for the elements of the first and second rows of the periodic systernla and for the elements of the first transition series1= show that such orbital electronegativities are considerably dependent on the character of the orbitals considered, and differences of more than one Pauling unit in electronegativity of the same atom but different hybrid orbitals are no exception. Consequently, it seems of interest to have available orbital electronegativities for different valence states for the heavier elements also. Furthermore, it has been indicated in the first article'" that, on the basis of Mulliken's definition, one has to
1502
JURGEN
HISZEASD H. H. J A F F ~
Vol. 67
TABLE I \-AI.ZKCE
K
Valence s t a t e
0.0 1.61
9
P
STATEPRONOTION ENERGIES IN= E.v.
Ca+
Valence s t a t e
0.0 3.13
SP PP didi dir trtr
K-b
Ca
So+
tete
2.43 1.52 1.73 1.97 1.82 1.82 1.80
2.15 4.86 1.91 3.51 2.95 3.96 3.45
1.88 8.21 2.09 5.04 4.08 6.09 5.10
SPP PPP didi 7 dirn trtrtr trtrtrr tetete
3.64 5 . 8 4 8.13 10.35 12.52 2 . 4 8 . 0 0 12.50 17.27 21.91 26.26 5 . 3 3 . 2 8 5.31 7.39 9.45 11.45 2 . 1 5.82 9 . 1 7 12.70 16.13 19.39 3 . 8 3.16 5 . 1 3 7.14 9.15 11.09 1 . 9 4.93 7 . 8 2 1 0 . 8 j 4.46 7 . 1 1 9.86 Ga-b
Ge
As+
SPPP didim trtrrr tetetete
4.10 4.24 4.28 4.30
6.58 6.37 6.30 6.26
8.48 8.18 8.08 8.03
As
Se+
SP PP didi dir trtr
tm
Zn-b
Ge-5
Ga
Ge+
trr
tete
As++
Se+++
S2PPP SP2PP di2dirT didin2T trZtrtrn trtrtrd te'tetete
0.92 3.52 2.22 3.43 2.61 3.39 2.80
S2P2PP SP2PZP di2di2rn di2didT dididd tr2trZtrn tr2trtrTZ te2te2tete
0.21 4.75 0.21 2.48 4.54 1.72 3.14 2.43
S2P2P2P SP2P2Pz
0.06 0 . 1 5 0.22 0 . 3 0 0.40 8.38 10.95 13.51 16.12 18.66
As-b
Se-b
Ca-E
0.89 0.86 7.48 11.45 4.19 6 . 1 5 7.14 10.85 5 . 1 3 7.65 7.02 10.65 5.58 8.3.5 Se
Br+
Rb
Kr+
Kr++
Rb++
2.04 4.46 1.83 3.25 2.75 3.65 3.20
3 . 6 3 6.10 7.70 12.51 3 . 1 1 5.57 5.67 9.30 4.76 8.00 6.34 10.37 5.53 9 . 1 7 2.4 R .3 2.1 3.8 1.9 3.2 2.8
SPP PPP didir dinn trtrtr trtrtrn tetete
s 2PP SP'P PLPP didir2 didn di%r di2dir tr2trtr tr2tr7r trtrn2 te2tete SPPP didira trtrtrr tetetete S2PPP SP'PP di2dinr didia% tr2trtrn trtrtrnz te2tetcte
0.39 0.39 0 . 6 5 8.22 12.05 15.34 0 . 3 9 0.39 0.65 4.30 6.22 8.00 7.75 11.28 14.33 3 . 0 0 4.28 5 . 5 5 5.40 7.82 10.00 4.18 6.03 7.74 Br
0.45 1.22 0.55 .84 .75 .97 .86
Sr+++
S2P2PP SPZP2P di2di2nn di2didr didids2 tr2tr2trr tr2trtrn2 te2te2tete
Sr+
0.0 0.0 s 2P2P2P 1.58 1.83 sp"2p 2 P a Calculations also have been made for valence states of the same elements with Iower valence; such values are contained in J. Hinze, Ph.D. Dissertation, University of Cincinnati, 1962. Extrapolated values. Roughly estimated values. S
expect considerably different electronegativity values for ions. To demonstrate this and to make available orbital electronegativities of some positive ions we have computed such values for the elements of the first two rows of periodic table. Procedure.-The evaluation of the orbital electronegativities with Mulliken's dcfinition has been described in detail in the first article of this series,la and only a short outline mill be given here. The essential part is the computation of the valence state ionization potentials, I,, and electron affinities, E,, or in the case of positive ions, the first and second valence
state ionization potentials, I,(1) and I , (2), respectively. (a) Orbital Electronegativities of the Neutral Elements of Rows Three and Four.-The valence state ionization potentials required are obtained from the ground state potentials, I,, and the corresponding promotion of energies of the positive ion and atom, Pf and Po,respectively, according to
I,
=
I,
+ P + - PO
(2)
and analogously the valence state electron affinities are calculated from the ground state electron affinities, E,,
ORBITALELECTROSEGATIVITIES OF SEUTRAL ATOMS
July, 1963
and the promotion energies of atom and negative ion, following
E,
=
E,
+ Po - 2’-
(3)
Here the valence state proniotion energies represent the energies required to elevate an atom or ion to the valence state, which, as defined by van Vleck,6 is the hypothetical “state” of an atom, chosen so that the interactions of the electrons of the atom are as nearly as possible the same as they mould be if the atom is part) of a molecule. The detailed description of the computation of such valence state promotion energies, following 1\Iulliken’s5and van Vleck’s6 method, has been given previously. la The Slater-Condon parameters used here for the computation of the promotion energies are those obtained and reported earliera7 It is again necessary to use the parameters determined from several configurations simultaneously, implying that equivalent parameters have the same value for the configurations. Although it is known that the assumption of the configuration independence of Slater-Condon parameters is questionable, it has been shown7that this assumption is acceptable on the level of the approximations inherent in the Slater-Condoii treatment. The proniotion energies of the negative ions, which cannot be computed directly, are obtained as described in the first articlela from a linear extrapolation of the corresponding promotion energies of successive states of ionization in an isoelectronic sequence. Such an extrapolation, however, is not possible for the promotion energies of Ca- and Sr-, since the necessary spectral information is not available for the isoelectronic positive ions. Consequently the promotion energies of Ca- and Sr- are estimated roughly, guided by the corresponding energies for Mg- and Be-, which are kn0wn.l“ All the promotion energies computed and used for the evaluation of valence state ionization potentials and electron affinities are given in Table I. Ground state ioiiization potentials, experimentally determined from spectral data, are accurately known. The values used here are chosen from Xoore’s tables.8 Unfortunately, the ground state electron affinities are not so readily obtainable, and only the yalues for Br and I have been determined e~perimelitally.~The values used for the other elements are those extrapolated by Ginsberg and Miller.1o The ground state ionization potentials and the electron affinities lised are listed in Table 11. With the entries of Tables I and 11, the valence state ionization potentials, valence state electron affinities, and the orbital electronegativities are readily obtained using eq. 1, 2 , and 3. The results are listed in Table 111, where the last column gives the electronegativities in Pauling units, more familiar to the chemist. The transformation used isla
xp = 0.336(xm - 0.615)
(4)
(b) Orbital Electronegativities of the Positive Ions (6) J. H. v a n Vleck, J . Chem. P h u s . 2, 20 (1934). ( 7 ) J. Hinre a n d H. H. JaffB, ihid., 38. 1834 (1963). ( 8 ) C. E. Moore, “Atomic Energy Levels,” Kational Bureau of Standards Circular KO.467, Vol. 1-111, a n d private communication. (9) T. L. Bailey, J . Chem. Phus., 28, 792 (1958). (10) A . P. Ginsberg a n d J. AT. hIiller, J . Inarg. Nuel. Chem., 7, 351
(1958).
1503
TABLE 11 GROUNDSTATEIOKIZATION POTENTIALS AND ELECTRON AFFIXITIES IK (E.V.)
x Ca Ga Ge AS
Se
Br Rb Sr In
Sn 8b Te
I
Z g
le
0.00 .ll .18 1.20 0.65 2.20 3.55 0.00 0.10 0.20 1.00 1.10 2.30 3.21
4.34 6.11 6.00 7.88 9.81 9.75 11.84 4.18 5.69 5.78 7.34 8.64 9.01 10.45
of the Elements of Rows One and Two.--The evaluation of the orbital electronegativities for the positive ions of rows one and two of the periodic system is essentially the same as described above. However, it is much simplified, since the promotion energies required, of atoms and singly and doubly positive ions, have already been computed,l*and the ground state first and second ionization potential can be taken from Moore’s tables.* Thus, it is merely necessary to combine all these data analogously to eq. 2,3,and 1to evaluate the valence state ionization potentials and orbital electronegativities of the positive ions. The results obtained are listed in Table IV, where again the last column give$ the electronegativities in Pauling units, converted using eq. 4. Discussion The Mulliken definition of electronegativity is the only non-empirical one available, and has received wide acclaim and acceptancel1,l2;it is the only readily available scheme for distinguishing between different hybrids and different types of orbitals. However, in considering the problems of evaluation of electronegativity it frequentlyhas been pointed out that the Mulliken electronegativity is difficult to compute because electron affinity data are required which frequently are not available. This apparent limitation of the Mulliken definition, however, is not a t all serious. Generally the electron affinity can, by purely empirical guesswork, be estimated to within 1e.v., and the resulting uncertainty in electronegativity is only of the order of 0.16 Pauling unit. Thus, any uncertainties in the electron affinity obtained in the present work have very little effect on the resulting electronegativities. The electronegativities obtained in the present work and listed in Table I11 for the neutral atoms of rows three and four, and in Table IV for the positive ions of rows one and two of the periodic system, show the considerable dependence on valence states that would be expected from the similar behavior of the electronegativities of the neutral atoms of rows one and two reported previously.la Again, as already reported for the first two groups, the valence state electronegativities are linear functions of the hybridization parameter. It seems of particular interest to compare the electronegativities obtained in this work with values for group (11) C. A. Coulson, “Valence,” Clarendon Press, London, 1952. (12) 11. 0. Pritchard a n d H. A. Sklnner, Chem. Rev., 55, 745 (1935).
JURGEN HINZEAND
1504
H. H. J A F F ~
TABLE111
VALENCESTATEIONIZATION POTEXTIALS, ELECTRON APFINITIES, AKD ORBITALELECTRONEGATIVITIES OF ELEMENTS OF Row 3 AKD
Orbital
I,
E"
XP
8
8
P
P
SP
8
4.34 2.73 7.09 3.96 4.38 5.76 5.73 4.16 5.25 5.28 4.25 5.01 14.58 6.75 7.92 11.19 6.58 11.25 7.33 9.76 9.99 7.07 9.22 18.57 9.43 14.21 8.89 12.43 8.72 11.46 9.36 16.22 12.16 13.39 10.75 14.53 12.19 13 .OO 11.24 13.84 12.80 11.68 20.49 14.44 11.68 17.29 13.06 17.94 15.68 12.59 16.28 16.29 13 10 22 07 4 18 2 60 6.62 3.6d 4.20 5.34 41 3.92
1.46 0.77 2.26 -0.24 -0.53 1.02 0.42 - .38 .06 - .13 - .33 - .04 5.57 1.78 8.40 3.15 1.10 7.25 5.09 2.28 5.13 3.69 4.02 6.86 4.26 5.35 4.14 4.89 4.11 4.66 1.33 7.92 3.38 4.63 2.36 5.31 3.25 4.06 2.64 4.53 3.81 2.52 10.36 2.04 2.52 6.44 2.28 5.73 5.14 2.37 4.77 4.24 3.70 14.50 0 1.84 2.14 -0.36 - .94 .93 15 - 65
0.77 0.38 1.36 0.42 .65 .93 .83 .43 .68 .66 .45 .63 3.18 1.22 2.54 2.20 1.09 2.90 1.88 1.82 2.33 1.60 2.02 4.06 2.09 3.08 1.98 2.70 1.95 2.50 1.59 3.84 2.40 2.82 1.99 3.13 2.39 2.66 2.12 2.88 2.58 2.18 4.97 2.56 2.18 3.78 2.37 3.77 3.29 2.31 3.33 3.07 2.62 5.94 0.50 0.54 1.26 0 34 .34 .85 .73 .34
Configuration
PP didi din
P P U U
7r
trtr trn
U U 7r
tete SPP PPP didir
U
8
P P U
7r
dirr
U
7r
trtrtr
U
trtrn
U 7r
tetete SPPP
U
8
P didim
U 7r
trtrtrn
U
7
tetetete S2PPP 8PZPP
U
P 8
P dizdi*r
U A
didir%
U
r
tr2trtrr
U
7r
trtrtr+ teztetete $2P2PP SP2P2P
U U
P 8
P
diZdi2nA diZdir%
7r U
T
didiiA2 tr2tr2trr
U U
7r
Wtrtrd te2te2tete S2P2P2P
P
SP 2P2P
S
S
S
P
P
5P
8
PP didi diT
U
U
P P U U ?r
"
4" Configuration
Orbital
trtr
U
trr
U ?r
tete SPP PPP didir
U
8
P P U
7r
dim
U
7r
trtrtr trtrx
U U
7r
tetete 8 zPP SPZP P2PP didirz dix%
U
P 8
P P U U
X
di%T di2din
7r U
7r
tr2trtr tr2trT
U
U
7r
trtrx2 te2tete SPPP
U U
8
P didirT
U
trtrtrA
U
7r
7r
tetetete S2PPP 8P2PP
U
P 8
P
dizdi7r7r
U A
didi7A
U
7r
tr2trtr7r
U
7r
trtrtrT2 te2tetete S2P2PP SP 2P2P
U U
P 8
P
di2diZm dindiAz=
x U
7r
didi A A ? tr2tr2trT
U
U
7r
tr2trtr7r2 tls2te2tete SZPZP2P SP 2P2P
U U
P 8
I" 4.92 5,Ol 4.02 4.72 12.60 6.19 6.62 9.84 6.11 9.61 6.40 8.68 8.67 6.30 8.10 6.94 16.34 8.51 12.10 12.81 14.22 10.30 10.15 13.04 7.90 11.43 12.65 9.50 12.49 11.57 16.16 8.32 12.64 8.10 11.17 8.02 10.40 8.75 18.80 11.68 15.27 10.21 15.56 11.25 13,89 10.51 14.16 13.16 11.04 20.78 14.80 11.04 17.12 12.91 18.19 15.36 12.29 16.26 15.11 12.67 18.00
Ev
XP
- .15 - .46 - .65 - .30 5.83 0.52 3.01 2.79 0.40 3.82 1.76 1.89 2.67 1.29 2.08 0.87 7.94 5.54 10.11 6.35 8.92 7.82 6.15 4.40 3.20 4.61 6.55 5.80 7.64 6.16 7.72 5.33 6.15 5.00 5.64 4.89 5.39 1.18 7.51 3.62 4.35 2.41 5.25 3.52 3.97 2.77 4.58 3.79 2.55 9.09 2.93 2.58 5.84
.59 .56 .36 .54 2.88 0.92 1.41 1.91 0.88 2.04 1.16 1.57 1.70 1.07 1.50 1.10 3.87 2.15 3.52 3.01 3.68 2.84 2.53 2.72 1.66 2.49 3.02 2.36 3.17 2.77 3.80 2.08 2.94 1.99 2.62 1.96 2.44 1.46 4.22 2.36 3.09 1.91 3.29 2.27 2.79 2.02 2.94 2.64 2.08 4.81 2.77 2.08 3.65
2.76 5.61 4.75 2.70 4.69 4.20 3,52 13.38
2.43
3.79 3.17 2.31 3.31 3.04 2.52 5.06
See footnote a, Table I.
IV elements obtained empirically by other ~ 0 r k e r s . l ~ sistently somewhat higher than the empirical values (Ge 2.0, 1.8-1.9; SnIV 1.9, 1.8). This fact may, most Our values for tetrahedral Ge and Sn are seen to be conlikely, be ascribed to some hybridization with d-orbitals (13) R. 8. D r a m , J. Inorg. ~Yucl.Clrem.., 18. 237 (1960); A . L. Allredand in the heavy elements; the d-orbitals have low ionizaE. C. Rochow. ibid., 6, 269 (1958).
ORBITALELECTROSEGATIVITIES OF SEUTRAL ATOMS
July, 1963
1505
TABLE IV ELECTRONEGATIVITY ASD IONIZATION POTEA-TIALS OF POSITIVE 10x3 Ion
Configuration Orbital
Be +
S
S
B+
P SP
P
PP didi diP
8
P P U
U P
trtr trn
U U
P
C+
tete SPP PPP didir
U
S
F P U
a
diPP
U
P
trtrtr trtrr
U
U
a
N+
tetete SPPP
U
S
P didim
U
P
trtrtra
U
P
o+
tetetete S2PPP SP”P
U
P 9
P di2diPP
U
P
didiP%
U
P
tr2trtrP
U
P
trtrtrP2 te2tetete
U U
Iv
E”
18.21 14.25 25.40 19.40 18.91 23.48 22.16 19.16 21.72 21.08 19 08 20.93 33.03 23.93 23.29 29.85 23.86 28.16 23.61 28.14 27.36 23.68 26.71 41.84 28.69 37.00 28.70 34.62 28.71 33.29 34.15 51.41 34.22 46.80 34.19 44.56 33.95 42.49 34.08 41.39 40 31
9.32 5.32 14.05 7.38 7.37 9.64 8.94 7.37 8.33 8.02 7.37 7.88 19.42 9.91 11.65 13.29 9.83 12.96 10.78 11.83 11.91 10.45 11.37 25.59 12.48 17.24 12.06 15.09 11.96 14.14 14.61 32.29 15.86 23.45 15.24 22.34 15.53 20.15 15.30 19.64 18.70
XP
6.10 3.08 6.42 4.29 4.21 5 36 5.02 4.25 4.84 6.36 4.23 4.63 8.60 5.48 5.66 7.04 5,45 6.70 5.57 6.50 6.39 5.52 6.19 11.12 6.69 8.90 6.64 8.l:i
6.63 7.76 7.98 13.86 8.21 11.59 8.10 11.03 8.11 10.32 8.09 10.05
9.70
tion potentials and electron affinities, and hence must have low orbital electronegath-ities. Even a relatively small contribution of such orbitals m7ould consequently be expected to significantly depress the electronegativity. Unfortunately, a calculation of d-orbital electronegativity by the hlulliken method is not feasible, because the necessary spectroscopic data are not available. Finally, the sensitivity of the electronegativity of the heavy elements to d-orbital hybridizationLCindicates that their electronegativities need to be considered as especially variable, since this hybridization itself is a sensitive function of many factors, e.g., the formal charge.’4 The electronegativities calculated for the positive ions are, as might have been expected, considerably higher than for the neutral atoms. The magnitude of the difference may :seem somewhat surprising, ranging from about a factor of 3 for the early members in a period to a factor of 2 in the late members. It must, however, be realized that these values refer to integral positive charges not compensated by inductive effects or ionic character, and are calculated from data appli(14) H H Jade, J P h y s C h e m , 58, 185 (19541, D P Craia and C Zauli, J . Chem Phys , 37, 601, 609 (1962)
Ion
Mgf
Al+
Configuration Orbital
s P sp PP didi dir
S
P S
P P U U
T
trtr tr
U U
P
Si+
tete spp PPP didir
U
S
P P U
T
U
a
trtrtr trtrn
U U
P
Pf
tetete SPPP
U
S
P U P
trtrtra
U
P U
P 6
P U P
didi T 2 P
U
P
te2teteP
U
P
trtrtrP2 te’tetete
U U
I”
15.03 10.60 20.15 13.48 14.34 17.47 17.25 13.92 16,28 16.28 14.06 15.75 24.68 16.56 16.56 21.43 16.50 20.62 16.55 19,96 19.62 16.53 18.97 31.24 20.72 27.01 20.69 25.14 20.68 24.10 22,91 35.18 24.49 31.57 23,70 30.61 24,OO 28.99 23,74 28.51 27.65
E.”
7.64 4.67 11.32 5.99 6.03 8.00 7.59 6.00 7.01 6.74 5.92 6.64 14.93 8.61 11.42 10.95 8.60 11.56 10.02 9.99 10.57 9.54 10.08 18.61 11.55 14.05 10.96 12.72 10.76 12.09 11.05 21,13 11.98 16.09 11.51 15.78 11.92 14.38 11.65 14.33 13.64
XI,
3.60
2.36 5.08 3.07 3.21 4.07 3.97 3.14 3.70 3.68 3.17 3.56 6.45 4.02 4.49 5.23 4.01 5,20
4.26 4.83 4.87 4.17 4.67 8.17 5.22 6.69 5.11 6.15 5.08 5.88 5.50 9.26 5.92 7.80 5.71 7.59 5.83 7.08 5.74 6.99 6.73
cable to the gaseous state, whereas the electronegativities are to be used generally for molecules in solution. Obviously, effects such as stabilization by solvat ion with polarization (charge shift) of solvent molecules may appreciably affect these values. It may further be worth noting that the ion coinmouly encountered as an intermediate in organic chemistry, say C(tr,tr,tr). An electronegativity can also be obtained for an “ion” in which the charge is accumulated on the central atom by inductive charge The electronegatransfer, l b say C(trz/atrz/atr*/a~). tivity of an “ion” formed in this way tends to be slightly lower than for the more normal one; thus, as a comparison x[C+(tetete)] = 6.19; ~ [ C + ( t e * ’ ~ t e ’ ’ ~ t e ~ = ’ ~ t6.11 e)] Acknowledgments.-This work was supported by a contract with the Wright Air Development Division, United States Air Force, Wright Patterson Air Force Base, Dayton, Ohio. The authors are grateful to Dr. Ivan Goldfarb and Dr. J. T. Zung for much preliminary work; to Dr. M. ,2.Whitehead for helpful discussions, and to Mr. Bernard Free and Mr. Charles Schare for technical help. The assistance of the Uni-
1506
D. R. FREDRICKSON, R. L. NUTTALL, H. E. FLOTOTV, AKD W. X. HUBBAKD
versity of Cincinnati Computing Center aiid Grant G19281 from the Sational Science Foundation in carrying
Vol. 67
out the extensive computatioiis necessary is also gratefully acknowledged.
THE ENTHALPIES OF FORMATIOX OF 23[RCcOSIUJI DIHYDRIDE AND ZIRCONIUM DIDEUTERIDE' BY DOSALDR. FREDRICKSOS, RALPH L. SUTTALL, HOTYARD E. FLOTOW, ASD WARDS.HLTBBARD drgonne iVatzonal I,aboratoiy, Argonne, Zllznozs
Receabed Januaiy 11, 1963 The standard energies of combustion of ZrH2 and Zrnl TI ere determined by precision osvgen bomb calorimem r e -290.03 Ij, 0.24 k u l . mole-' of ZrHl and -290.80 f 0.18 koal. mole-' try. The values found for 4EC0 of ZrD2. A t 298.15"K. the enthalpy of formation, A H p , and the Gibbs energy of formation, AGfO, mere calculated to be -38.90 + 0.31 kcal. mile-' and -29.32 =t0.31 kcal. mole-', respectively, for ZrH2, and -40.22 =t 0.27 kcal. mole-' and -29.86 i 0.27 kcal. mole-', respertively, for %rDl.
Introduction The heat of cornbustion of ZrH1,9?was measured a t 18" by Sieverts, Gotta, and I-Ialberst~adt.2 They reported an energy of combustion of -282.0 kcal. mole-l for this material. They also measured the energy of combustion of zirconium using the same source niat,erial as was used to make their hydride. The energy of combustion of this zirconium was - 2 5 5 . 5 kcal. mole-l. Using the above values for xircoiiium and ZrR2 and a value of -67.57 kcal. mole-' for the energy of formatioil of water. they calculated enthalpy of formation values of -38.9 kcal. mole-' of ZrH,,,, and -40.5 kcal. mole-' of ZrH2. Yo calorimet'ric data leading to the enthalpy of formation of ZrD2 have been published. Equilibrium hydrogen pressures at Yarious H 'Zr atomic rat'ios in the temperature range 600 to 1200°1C have been measured by a iiuniiser of investigators. These data can be used to obtain partial molal ent'halpies of solution of hydrogen in the hydride phases. These partial molal enthalpies of solution can be integrated over the coniposition range to give the enthalpy of formation of a particular hydride. 1\Zartinand R e e ~ reported a value of -41.4 kcal. mole-' for the enthalpy of formation of ZrH?. Morton and St'ark? have nieasured equilibrium dissociation pressures for deuterides with D/Zr atomic ratios between 0.02 and 1.80. They report partial molal enthalpies of solution of deuterium over this coniposit,ionrange. On the basis of their data, we estimate the enthalpy of formation of ZrD2 to be about -42 kcal. mole-'. Because of uncertainties due to samp!.e impurities, experimental errors, and approximations, all of the above values of AHfO are believed to he uncertain by a t least f3 kcal. mole-1. It therefore seemed worthwhile to determine these eiit halpies more mxrately by using purer samples and precision bomb calorimetry. (1) This work was performed under the auspices of the U. S. Atoniic Energy Commission. (2) A . Siei-erts, A. Gotta, and 9. Halberstadt, Z . anorg. alloem. Chem., 187, 189 (1930). (3) (a) A . Sieverts a n d E. Itoell, ibid., 153, 289 (1926); (b) 11. N. A. Hall, S. L. H. Martin, and A. L. G. Rees, Trans. Faraday Soc., 41, 306 (1945); ( e ) S. L. H. Martin and A. L. G. Rees, ibid., 50, 343 (1954); (d) R. K. Edwards, P. Levesque, and P. Cubiociotti, J . Am. Chem. Soc., 7 7 , 1307 (1955); ( e ) E. A. Gulbransen and K. F. Andrew, J . N e t a h , 7 , 136 (1956); ( f ) C. E. Ells and A. D. MoQuillan, J. Inst. Metals, 85, 89 (1956-87); (6) 1vI. W. R'Iallett a n d W. 1LI. Albrecht, J . Electrochem. Soc., 104, 142 (1957); (11) L. D. LaGranpe, L. J. Dykstra, J. M. Dixon, and U. AIerten, .I. Phf18. Cham., 63, 2035 (1959); (i) G. G. Libowitn, J. Nucl. Mater., 6 , 2 (1962). (4) J . R. Morton and D. S. Stark, Trans. Faraday Soc., 66, 351 (1960).
This paper describes measurements of the energies of reaction represented by the equations ZrHz(s)
+ 3,'202(g)
ZrDz(s)
+
ZrOn(s)
+ HzO(1)
(I)
202(g) = ZrOz(s)
+ DzO(1)
(2)
=
aid at 298.15"Ii. These data mere combined with other appropriate thermodynainic quantities to calculate riitlialpies of formation, AHfO, a t 298.15 OK. aiid a t 0°K. and the Gibbs energy of formation, AGfO, a t 298.15"K. of ZrH2 and Zrll?. The uncertainty in the value of AHiO for ZrHS reported in this paper is about an order of magnitude less than the values reported previously. The difference between the AHfO of ZrH2 and that of ZrDz a t 298.15"K. calculated from these results agree with the difference calculated6 from heat capacity data. Experimental Samples.-The ZrHl and ZrDp samples which were used for the heat of combustion measurements reported in this paper ~were ~ previously used a t this Laboratory for heat capacity deterniinations.6 It was found6 by analyses that the impurities in each sample amounted to less than 0.1%. The compounds as originally prepared were in the form of irregular pieces whirh varied in size from about 0.1 to 3 mm. on an edge. Preliminary attempts to burn this material in the combustion bomb were unsatisfactory because some of the hydride pieces exploded and the scattered fragments did not burn completely. This difKculty was eliminatod by burning powdered samples of particle size 100 p or less. The powdered material with its concomitant large surface area was found to oxidize a t a measurable rate in air. The samples were therefore prepared, weighed, and sealed in plastic bags in a helium-filled drybox where the combined oxygen and water concentration was lesR than 0.1%. ZrHz is hard and brittle and i t was found convenient to prepare powdered samples in the drybox by crushing the ZrHz and ZrDZ with a hardened steel pestle on a hardened steel plate. Particles which would pass through a 240 mesh brass screen but which were retained on a 400 mesh brass screen were used for the calorimetric measurements. Spectrographic analyses of the powdered ZrHz and ZrUz samples showed that both samples contained, within the error of the analyses, the same impurity levels. The elements detected were present in amounts equal t o the follouTing in parts per million: Mg, 3; Cu, 40; Fe, 200; and Pb, 40. Other elements looked for, but not detected, are given with the lower limits of detection in reference 5 , Chemical analysis of the ZrHz showed 564,19, and 170 parts per million of oxygen, nitrogen, and carbon, respectively. For ZrDy the results of the chemical analyses f o r ( 5 ) H. E. Flotow and D. W. Osborne,
J. Chem. P l a ~ .$4, , 1418 (1961).
