PREDICTED PROPERTIES O F THE SUPER
1127
HEAVYELEMENTS
Predicted Properties of the Super Heavy Elements. I. Elements 113 and 114, Eka-Thallium and Eka-Lead1 by 0. L. Keller, Jr., J. L. Burnett, T. A. Carlson, and C. W. Nestor, Jr. Oak Ridge National Laboratory, Oak Ridge, Tennessee 87830 (Received June 11, 1969)
The probable existence of an island of nuclear stability centered on element 114 makes the prediction of chemical and physical properties of elements in this region important for their identification. These elements may be produced using proposed heavy ion accelerators,or they may even be found in nature. The values derived from extrapolations in Mendeleev’s periodic system and theoretical calculations are presented in the following table.
Chemical group Atomic weight Most stable oxidation state First ionization potential, eV Second ionization potential, eV Oxidation potential, V
Metallic radius, A Ionic radius, A Atomic volume, cm* (g-atom)-’ Density, g/cm3 MP, OK BP, “K Heat of vaporization, koa1 (g-atom)-l Heat of sublimation, kcal (g-atom)--I Debye temp, OK Entropy, ea1 deg-1 (@;-atom)-’ (25’)
A number of theoretical papers2 have appeared recently indicating that islands of nuclear stability exist around elements 114 to 126. Several laboratories in the U. S., Western Europe, and Russia are proposing to build heavy ion accelerators to explore this region of t h ? periodic table. Work is also progressing here and abrotd in the search for super heavy elements in nature. As an aid in designing experiments for the necessary chemical identification of the accelerator products and to assist in the search for possible naturally occurring isotopes of the super heavy elements, we present in this and succeeding papers values for certain physical and chemical properties predicted on the basis of Mendeleev’s periodic system and theoretical calculations. In this first paper, we present our results for elements 113 and 114. Ionization Potentials Element 114 occurs in group IVA of the periodic system. The eigenvalues of Ge, Sn, Pb, and 114 free atoms and their free + l ions have been calculated using a relativistic Hartree-Fock-Slater (HFS(Re1)) program developed a t Oak Ridge.3 The Slater-Latter approximation with an exchange factor of 1.5 is used
Element 113, Eka-Thallium
Element 114,Eka-Lead
IIIA
IVA 298 +2
297 +1 7.4 M +M+ -0.6 1.75 1.48 18 16 700 1400 31 34
70 17
+ e-
8.5 16.8 M 4M2+
+ 2e-
-0.9 1.85
1.31 21 14 340 420 9 10 46 20
for the exchange potential. A 7s27p2configuration for 114 was assumed in accordance with the relativistic Dirac-Slater calculations of Waber, Cromer, and Liberman.4 The eigenvalue of the PIISelectron is taken as an approximation to the ionization potential. The theoretical and experimental ionization potentials together with their differences are presented in Table I. The A’s for 114 were obtained by extrapolating the A’s of Ge, Sn, and P b with the best straight line to 114. These A’s were then used to obtain the “experimental” ionization potentials of 114. Our procedure for obtaining a semiempirical value of the first ionization potential for element 114 was also checked using eigenvalues from the relativistic HartreeFock solution (kindly supplied by Joseph €3. Mann from (1) Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Gorp. (2). (a) For an excellent review see G. T. Seaborg, Ann. Rev. Nuclear Scc., 18, 53 (1968); (b) 8. G. Nilsson, S. G. Thompson, and C. F. Tsang, Phys. Lett., 28B,458 (1969). (3) C. W. Nestor, T. C. Tucker, T. A . Carlson, L. D. Roberts, F. B. Malik, and C. Froese, “Relativistic and Non-Relativistic SCF Wave Functions for Atoms and Ions from 2 = 2 to 80,” 013”-4027; for a related paper using a Wigner-Seitz boundary condition see Pht s. Rev., 174, 118 (1968). (4) J. 7’. Waber, D. T. Cromer, and D. Liberman, ref 2a, p 105.
Volume 74, Number 6 March 6,1970
0. KELLER,JR.,J. BURNETT, T. CARLSON, AND C. NESTOR, JR.
1128 Table I : Ionization Potentials” (Group IVA)
---
HFS(Re1)
Ge Sn Pb 114 a
6.44 6.14 6.46 7.77
I Exptl
7.88 7.34 7.42 8.49
1 --
.c
HFS(Re1)
A1
1.44 1.20 0.96 0.72
14.63 13.54 14.07 15.97
Exptl
An
15.93 14.63 15.03 16.75
1.30 1.09 0.96 0.78
Values in electron volts.
Table 11: HFS(Re1) Eigenvalues (eV) of Outermost SI/,and Ds/, Electrons (Group IVA)
8%
@e
Sn
Pb
114
14.69
13.19 31.99
14.32 24.90
16.63 17.66
DS/Z
unpublished data). The extrapolated value obtained was within 0.3 eV of that given in Table I. The eigenvalues of the outermost and D,, electrons for the free atoms are listed in Table 11. It is seen that the eigenvalues for the s and p electrons are not approaching each other in energy as one goes t o higher atomic numbers although the s and d electrons are. This is important in the considerations of the valence of 114 where tetravalency requires promotion of an s electron for spahybridization. Since element 113, with a 7s27pc~nfiguration,~ occurs in group IIIA, the eigenvalues of the P1,, orbitals of Al, Ga, In, TI, and 113 were calculated using the HFS(Rel) program.8 The differences between the calculated and experimental values were extrapolated to obtain the first ionization potential of 113 (Table 111). To inspect the possibility of the formation of hybrid orbitals, the outermost and D6/, eigenvalues are Table XI1 : First Ionization Potential (vV) (Group IIIA)
A1 Ga
In T1 113
HFS(Re1)
Experimental
A
4.89 4.99 4.87 5.24 6.53
5.98 6.00 5.78 6.11 7.36
1.09 1.01 0.91 0.87 0.83
Table IV : HFS( Rel) Eigenvalues (eV) of Outermost SI/,and Ds/, Electrons (Group IIIA)
A1
Ga In Ti 113
S1/a
DS/l
10.2 11.66 10.7 11.99 14.5
26.78 24.4 19.42 14.4
The Journal of Physical ChemGtry
given in Table IV. Although the d and s orbitals approach each other in energy with increasing 2, their difference from the p electron remains large as in the 114 case.
Validity of Extrapolations to Elements 113 and 114 We estimate the properties of elements 113 and 114 mainly by extrapolating the properties of the lighter members of the respective groups to which 113 and 114 have been assigned. The basic validity of such extrapolations rests on this assignment. The most important evidence available on this question is contained in Tables I-IV. The results of our “state of the art” HFS(Re1) calculations show that the 7p electrons have a markedly different energy than the 7s and 6d. The p electrons are therefore the valence electrons which we expect to be the necessary condition to allow extrapolations in the periodic table. Oxidation States The outstanding periodic characteristic of the group IVA elements is their increasing stability in the I1 oxidation state relative to the IV as one goes t o higher atomic numbers. C and Si are almost always tetravalent, and Ge shows only very weak ciivalency. Sn chemistry is about evenly divided between divalency and tetravalency, and Pb is most stable in the I1 state with only weak tetravalent qualities. Drago6 shows from thermodynamic considerations that this trend arises from a decrease in the strength of the covalent bonds formed by the metal atom as the atomic number increases in this group. From the point of view of valence bond theory, the tetravalent state is made possible by sp8 tetrahedral hybridization. I n order for all four valence electrons t o be used in bonding, strong enough covalent bonds must be formed to supply both the promotion energy for one s electron and the Gibbs free energy required for compound stability. When only weak covalent bonds can be formed, as in most lead compounds, only the p electrons participate in bonding. Drago explains the weakening of the covalent bonding with increasing Z with the following two considerations. (1) In the higher 2 elements the valence electrons are spread over a larger volume so that less overlap with the orbitals of the anion results. (2) The heavier elements have more inner electrons to repel the inner electrons of the bonded anion. Since 114 has the largest atomic volume and the most inner electrons of any group IV element, sp3 hybridization will probably be very unimportant and thus element 114 will be weakly, if at all tetravalent. The expected most stable valence of 114 is +2. However, since the outermost s and d electrons in 114 have approximately equal energies, it may be possible to form a volatile hexafluoride. (5)
R.S.Drago, J . Phys. Chem., 62,353 (1958).
1129
PREDICTED PROPERTIES OF THE SUPERHEAVYELEMENTS The stable oxidation state of the group IIIA elements tends toward +1 from +3 with increasing atomic number. The +3 state is attained through sp2 trigonal hybridization. Drag06 shows that the trend toward $1 stability in the IIIA elements arises from the same considerations that explain the tendency toward +2 stability in the IVA elements. The most stable oxidation state for element 113 is therefore expected to be +l. As in the case of 114, however, we also suggest the possible existence of a volatile hexafluoride.
Metallic and Ionic Radii Metallic radii for 12-coordination are given by wellsa and Pauling’ (Table V). Since 114 is expected to have, like Pb, a cubic close-packed structure (facecentered cubic) the 12-coordinate radii are the proper ones for extrapolation. We assume that the change in radius between P b and 114 will be the same as between Sn and P b since similar electronic configurations are passe$ over in each case. We take the metallic radius (1.85 A) as the average of the Pauling and Wells values. The ionic radii’ can be extrapolated in a similar manner to obtain 1.28 A as the crystal radius of 1142+. There is a relation between ionic radii and 12-coordinate metallic radii of Ge, Sn, and Pb, however, in that their difference is 0.50 (Table VI). This indicates that the ionic radius of 114 should be 1.35 A. We take the average of the extrapolated and calculated values, 1.31 A, as the ionic radius of 1142+. We assume that 113 has a hexagonal closest packed structure like thallium. The 12-coordinate metallic radii given by Wellse for I n and TI extrapolate to a metallic radius of 1.75 1 for 113 (Table VII). The ionic radii’ extrapolate to 1.48 d. Extrapolating
Table VII: Radii
Ga In
T1 113
Metallic (Wells), A
Ionio (Pauling),
1.53 1.67 1.71 1.75
1.13 1.32 1.40 1.48
A
Pauling
Ge
Ar
1.44
Wells
Sn
1.62
Pb
1.70
114
1.78
0.19 1.58
0.08
0.17 1.75
0.08
0.17 1.92
Av 1.85
Table VI: Ionic Radii Ionic radius, 8, (Pauling)
Ge Sn Pb
0.93 1.12
1.20
Pauling metallic radius minus ionic radius
0.51 0.50 0.50 Av 0.50
0.40 0.35 0.31 0.27
Density and Atomic Volume We assume 114 has the same structure as Pb, i.e., fcc with four atoms per unit cell. Using the metallic radius of 1.85 A, the density of 114 is calculated to be 14 g cm-8 and the g-atomic volume 21 cm3 (g-atom)-’ (Table VIII). Oxidation Potential The oxidation potentials of Sn, Pb, and 114 are obtained from the free energy of the reactions M(s)
+ 2H+(aq)
using the relation
-
M2+(aq)
+ Hdg)
(1)
AH - TAS (2) where AG = Gibbs free energy (eV) and E” = oxidation potential (V). The enthalpy change for the change in state (1) is, using the Born-Haber cycle AG = -2E”
+ (I + 11) +
AH =
AHhyd(M2+(g>>- 2AHhyd(H+(g)) -
- AHdi~d”Z(g))] (3)
where AHSzg8 = heat of sublimation of the metal at 298OK, I I1 = sum of first two ionization potentials, AHl,,d(M2+(g)) = hydration energy of the gaseous metal ion, AHh,d(H+(g)) = hydration energy of the gaseous hydrogen ion (-11.14 eV), IP(H(g)) = ionization potential of the hydrogen atom (13.595 eV), AHDiss(Hz(g)) = heat of dissociation of the hydrogen molecule (4.52 eV). The heat of sublimation of metallic 114 is obtained from the plot of the heats of sublimation of Si, Ge, Sn, and P b vs. row of the periodic table (Figure 1 and Table IX). The curve is fitted by the equation
+
A?
1.39 0.18
-
R(metal1ic) - R(ionic) to 113 yields 0.27. The 12-coordinate metallic radius minus 0.27 yields 1.48 A the same as the extrapolated value.
-2(IP)(H(g)) Table V : Metallic Radii for 12-Coordination (A)
R(metal1ic) R(ionic)
Wells metallio radius minus ionic radius
0.46 0.46 0.55 Av 0.49
AH,298= 105
- 14.9~+ 0
. 6~ 0~ . 7 ~ ’
(6) A. F. Wells, “Structural Inorganic Chemistry,” 3rd ed, Oxford University Press, Oxford, 1962. (7) L. Pauling, “The Nature of the Chemical Bond,” 3rd ed, Cornell University Press, Ithaca, N. Y., 1960. (8) C. S. C. Phillips and R. J . P . Williams, “Inorganic Chemistry,” Oxford University Press, Oxford, 1965.
Volume 74, Number 6 March 6, 1070
0. KELLER, JR.,J. BURNETT, T. CARLSON, AND C. NESTOR, JR.
1130
Table VI11 : Thermodynamic Quantities" of Groups IVA and IIIA Elements10-l2 AH,, Element
BP, OK
MP,
Si Ge Sn
2950(?) 3100 2960
1683 1210 505
Pb 114 A1 Ga In
2024 420 2720 2510 2320 1740 1400
T1 113
OK
kcal mol-'
Trouton's constant
79.9 69.4
25.8 23.4
42.88 9.3 70.2 61.2 54.1 38,74 31
21.2 22 25.8 24.4 23.3 22.2 22
600.6 340 932 303 429.32 577 700
V , cmg (g-atom) -1
8, OK
1.2.04 13.64 16.29
670 370 190 (white) 95 46 420 333 110 89 70
P, g
cm-a
2.330 5.3234 5.75 (@;ray) 7.29 (white) 11.34 14 2.71 5.91 7.3 11.85 16
18.27 21 10.0 11.80
15 76 17.22 18 I
a Bp, boiling point; mp, nielting point; AH.298, heat of sublimation; AH, heat of vaporization a t the bp; 0, Debye temperature; V , atomic volume; pI density.
Table IX: Oxidation Potential of Element 1 1 4 " ~ ~
Element
AHp
cner&y
AHhyd (M"+(d)
Sn Pb 114
3.12 2.03 0.44
21.97 22.45 25.24
-15.8 -15.1 -14.3
Calculated Experimental oxidation oxidation potential (eq 1) potential (sq 1)
- TAS
Ionization gDM'+(aq)
x
-(i.7
5.3 6.7 8.7
0
2.2
x
(eq 1)
PM(S)
10-4) 10-4
x x x
10-4 10-4 10-4
" All quantities in appropriate units with energies in electron volts. b S o ~ z=( g13.5 ) X 2e- = Hz(g) is -9.4 eV.
-0.2 -0.2 -0.2
+0.15 +O.ll -0.9
eV deg-1.
+0.14 +0.13
Arf for reaction 2H+(aq)
+
Table X : Oxidation Potential of Element 113"~~
Element
AH8298
T1 113
1.86 1.47
Ionization energy
AHhdM ' ( 9 ) )
-Soh!+(as)
6.11 7.36
-3.22 -3.11
12.8 x 10-4 13.7 x 10-4
" All quantities in appropriate units with energies in electron volts. e- = 0.5€1&) is -4.7 eV.
+
where (x 3) equals the appropriate row of the periodic table. Letting x = 4 (for the seventh row) we (114) = 10 kcal (g-atom)-'. cal.culate AHSzg8 The hydration energy is calculated from the Born equation modified to give the correct oxidation potentials for Sn and Pb8 AHhyd=
2~~ - r 7+. 30.74
(4)
where z = charge on the ion and r = ionic radius (Pauling) (8). Calculated values are given in Table
6.6 X 7.4 x 10-4
Experimental oxidation potential
+0.35 -0.6
+0.34
-0.4 -0.4
AH for reaction H[+(aq)
0 . 5 8 ' ~ ~ (=~ 6.8 ) X 10-4 eV deg-1.
+
where the entropy of ideal diatomic hydrogen gas at 298°K = 31.21 cal deg-l mol-' (13.53 X lo-* eV deg-l); = entropy of the metal; and SoH+(nq) = 0 by con.vention. S O M ~ + ( the ~ ~ ) ,entropy of the aqueous metal ion, was calcuiated using the equation of Powell and Latimer.$ The standard entropy of 114 metal (20 eu (g-atom) -') was obtained by extrapolation of the entropies of Si, Gel Sn, and Pb vs. row of the periodic table (Figure 2 and Table 1x1
Som+(aq) = S/zRIn A
Tl7
+ 37 270-
lb.
(r
The entropy change for the change in state is (9)
The Journal of Physical Chemistry
- TAS
PM(8)
Calculated oxidation potential
2
+ 212 cal deg-I
(6)
R.E.Powell and W. M . Latimer, J . Chem. Phys., 19,1139 (1951).
PREDICTED PROPERTIES O F THE SUPER
1131
HEAVY ELEMENTS I
I
I
I
80 70 Ga
20
3
4 5 6 7 ROW IN PERIODIC TABLE
Figure 3. Heat of sublimation of element 113.
!-
4 e
5 6 7 ROW OF PERIODIC T A B L E
3
4
Figure 1. Heat of sublimation of element 114.
c
-
'a,
E !
W
Y
ii
0
r x tz 20
-
c
I
1
-aJ 15
!wi=
5
0 / I I A
c
3
4 5 e; 7 ROW OF PERIODIC TABLE
Figure 4. Entropy of elemental 113 (298°K).
where x = charge, A = atomic weight, and r = ionic radius (Pauling) , in Angstroms. The oxidation potential of 114 is calculated to be -0.9 V (American convention) (Table IX). The oxidation potential of 113 is obtained in a manner analogous to that used for 114. The hydration energies of T1 and 113 were ca$ulated using eq 4 with an additive constant of 0.87 A to the and ionic radius.8 The heat of sublimation, the elemental entropy were obtained by extrapolation (Figures 3 and 4 and Table X). The oxidation po-
PoGe , 3
4 5 6 7 ROW OF PERIODIC TABLE
Figure 2. Entropy of elemental 114 (298'B).
Volume 74, Mumber 6 March 6,1070
0. KELLER,JR.,J. BURNETT, T. CARLSON, AND C. NESTOR,JR.
1132
tential of 113 is calculated to be -0.6 V (American convention). Element 113 is therefore estimated to be somewhat more noble than thallium, being similar to copper in this respect (Cu = Cu+ e-; E” = -0.521
We obtain the melting point through the Lindemann melting point formula for close-packed meta1sl3
+
T,
V>*
=
02AV2/’ -
(7)
0 2
where O = the Debye temperature, A = atomic weight, V = molar volume, and D is found empirically to be about 120 cm g”’ OK1/’. The Debye temperature for Si, Gel white Sn, and Pb is plotted in Figure 5 using values from Mendelssohn.” We used the Dcbye
Boiling Points and Melting Points The boiling points of Si, Ge, Sn, and Pb do not lend themselves to extrapolation to 114. As seen in the discussjon of the oxidation potential, the heats of sublimation can be extrapolated. The heat of vaporization, AHv, is assumed to be 8.3% less than the heat of sublimation, the same as lead. Using Trouton’s rule and an entropy of vaporization of 22 eu, we calculate a boiling point for 114 of 420°K (Table VIII).lo-lz
700
1000 I
I
I
I
I
AI
900
c””-l
800 700
Tm
,OK
600 500 400
300
20c
Figure 6.
3
4
5
6
7
ROW OF PERIODIC TABLE Figure 5 .
Debye temperature of element 114.
The melting point of a substance is a structuredependent property and frequently is difficult to obtain by a simple extrapolation over a series where different structures are involved. Silicon, Ge, and gray Sn have the diamond structure; white Sn, which has typical metallic properties, is tetragonal, and Pb has the face-centered cubic (cubic closest packed) structure. We assume the latter for 114. The Journal of Physical Chemistry
3
4 5 6 7 ROW OF PERIODIC TABLE
Melting point of element 113.
temperature of white tin for our extrapolation. If gray tin (0 = 212OK) is used a negative 8 for 114 is obtained. Since white tin (tetragonal) has typical metallic properties whereas gray tin (diamond) does not, the use of the former may be sufficient to provide a transition between the diamond structures of Si and Ge to the fcc structure of P b allowing a reasonably ac(10) D. R. Stull and G. C. Sinke, “Thermodynamic Properties of the Elements,” American Chemical Society, Washington, D. C., 1956. (11) K. Mendelssohn, “Cryophysics,” Interscience Publishers, Inc., New York, N. Y., 1960. (12) 0 . V. Samsonov, “Handbook of the Physicochemical Properties of the Elements,” IFI/Plenum, New York, N. Y., 1968. (13) N. H. March, “Liquid Metals,” Pergamon Press, Oxford University Press, Oxford, 1968.
1133
PREDICTED PROPERTIES OF THE SUPER HEAVYELEMENTS curate extrapolation to 114. The data are fitted by the equation
e
=
670 - 3 7 2 ~- 7 8 ~ ’- 6x3
+
where (x 3) = row of the periodic table. Letting x = 4 gives 0 = 46°K for 114 and a melting point of 340°K (TableVIII). Although Ga is orthorhombic, I n is tetragonal, and T1 is hexagonal, their melting points extrapolate in a straight line to a melting point of 710°K for 113 (Figure 6). In this case, the Debye temperature of AI, Ga, In, and T1 could not be extrapolated. Extrapolating only In and T1 yields e = 70°K for 113. Using this value in Lindemann’s formula gives a melting point of 690°K. We take the average of 700°K as the melting point of element 113. The heat of sublimation, (AH,298), of 113 is obtained by extrapolation to be 34 kcal mol-1 (Figure 3). The heat of vaporization is assumed to be 10% less (AH, = 31 kcal mol-’). Using a Trouton’s constant of 22, the boiling point is calculated to be 1400°K (Table X).
Discussion In general, the chemistry of 114 is expected to be similar to that of divalent lead. The calculated oxidation potential of -0.9 V indicates, however, that 114 is considerably more noble. The large negative oxidation potential coupled with a large polarizability should enable 1142+to form strong complexes with anions in spite of its large ionic radius. In excess halogen acid, for example, complexes of the type 114X,(”-2)- should be quite stable. A complex analogous to the plumbite ion is also expected. The sulfate and sulfide should be extremely insoluble. The acetate and nitrate would be soluble. The covalent nature of the acetate should prevent hydrolysis, as in the case of lead, but the nitrate may show extensive hydrolysis. The chemistry of 113 is expected to be similar to that of the thallous ion although 113+ should form complexes more easily. Our predicted radius of 113+ is 1.48 A, the same as Rb+, and is not much larger than T1+ itself (1.40 A). The large polarizability and moderately large negative oxjdation potential of -0.6 V will increase the binding of anions to 113+, but the large radius will counteract these effects to quite an extent. For example, the solubility of TlCl in water is not increased by adding hydrochloric acid or ammonia in contrast to the behavior of AgC1. The 113+ ion should tend toward the behavior of Ag+ in these properties. The chloride, bromide, iodide, sulfide, and chromate of 113+ should have low solubilities while the nitrate and fluoride should be quite soluble. Thallous hydroxide is soluble and a strong base. The 113+ ion may, however, form only a slightly soluble oxide whose solution is alkaline readily absorbing carbon dioxide from the air. Like argentous and aurous oxides, the oxide of 113+ may be soluble in ammonia,.
Uncertainties in Predicted Properties Although the fundamental validity of extrapolation in the periodic table to the properties of 113 and 114 appears well founded, it is nonetheless difficult within the scope of this paper to discuss all of the assumptions and uncertainties in each of our estimates. There are two estimates, however, which appear to us to be questionable, and we will discuss those in some detail. The worst case is probably the melting point of 114 because we had to use (with little justification) the Debye temperature of white tin rather than gray tin in the extrapolation. The Lindemann melting point formula is a further approximation. Although there are difficulties with the method, the melting point itself appears acceptable from an intuitive point of
tL 0.5
L
4 5 6 7 ROW OF PERIODIC TABLE Figure 7. Row correlation of heats of sublimation of 113 and 114.
view. I n the other questionable case, the heat of sublimation (and boiling point) of 114, the opposite is true. Although the extrapolation appears to be reasonable, the results appear from an intuitive point of view to be far too low. The extrapolation was carried out (Figure 1) by fitting a polynomial, the only other method being “eye-balling.” The latter method allows the investigators judgment to be exercised to the maximum, and a value perhaps as high as about 20 kcal/mol-’ could be obtained. Thus the “eye-balling method could increase by as much as about 100%. Since the polynomial fits the dasta in a perfectly smooth and satisfactory way, however, it is difficult to see why we should not let the periodic Volume 74, Number 6 March 6,1970
J. W. F. VAN INGEN AND W. A. CRAMER
1134 table govern the extrapolation rather than our “intuition ,” There is, however, another way to extrapolate to A g e z g 8 of element 114. This involves essentially correlating by row as well as by column. If the ratio of the heats of sublimation for corresponding elements in groups IIIA and IVA are extrapolated to the seventh row (Figure 7), we obtain (by fitting a polynomial) a ratio of 0.87 for 114/113 (Figure 7). (Inclusion of the Si/Al ratio raises this ratio to 0.97.) The value of AHs298of element 114 obtained is 29.6 kcal mol-l, a value which cannot even remotely fit into the group IVA sequence (Figure 1). We must, therefore, choose between the two methods. The group IVA extrapolation (Figure 1) can be viewed as less reliable than the group IIIA extrapolation (Figure 3) since all group IIIA elements are metallic whereas group IVA elements are graded from nonmetallic to metallic. Unfortunately, in the row type of extrapolation (Figure 7), we are probably only emphasizing this discrepancy by taking ratios involving elements with quite different properties.
Since the properties of Si, Ge, Sn, and P b are more strongly correlated in a group way than in a row way, we accept the group extrapolation (Figure 1) as the more reliable method for predicting AH,298for element 114. Within this framework, we could, however, extrapolate only through Gel Sn, and P b leaving off Si. This would raise AH298to 15 kcal mol-’ (AHszg8= 90 - 1 4 . 5 ~- 3 . 5 ~ ~from ) our accepted value 10 kcal mol -I. Our other estimates do not involve such apparent problems. Although extrapolating across 32 elements involves a certain amount of bravado, and numerous assumptions are involved, we feel that our estimates are sufficiently accurate to prove useful in the search for superheavy elements.
Acknowledgment. It is a pleasure to express our thanks to Dr. Glenn T. Seaborg for suggesting this study. His insight and interest were important in the development of the ideas presented here.
Radiation-Induced cis-trans Isomerization of Solutions of 2-Pentene in Cyclohexane by J. W. F. van Ingen and W. A. Cramer Interuniversdair Reactor Instituut, Delft, The Netherlands
(Received September 8, 1969)
The cis-trans isomerization of solutions of 2-pentene in cyclohexane has been studied a t room temperature as a function of pentene concentration. Effects of various additives, notably CHsOH, NH,, piperidine, 0 2 , 1 2 , CCl+ C2H5Br,N20, C7FI4, and SFs were investigated. I n the presence of 12,C2HBBr,and SFa a chain reaction occurs, as is evident from the very high isomerization yields. A chain reaction is also observed in the 2537-A photolysis of solutions containing C2H5Brand 2-pentene. It is suggested that Br and I atoms and SF5 radicals act as chain carriers. I n the absence of a chain reaction, isomerization proceeds via excited 2-pentene molecules, formed by charge transfer from CsHI2+to the olefin and subsequent neutralization with electrons or negative ions.
Introduction Formation of hydrogen, cyclohexene, and dicyclohexyl from irradiated cyclohexane is reduced in the presence of olefins. In previous work we have investigated the y radiolysis of solutions of a number of olefins, including 2-pentene, with special emphasis on the effects of these additives on the hydrogen yield and the yield of saturated hydrocarbons corresponding with the o1efins.l Evidence has been presented that charge The Journal of Physical Chemistry
transfer from cyclohexane posit’iveions to olefins occurs if energetically possible. This can result in reduced decomposition of solvent) molecules and in sensitized reactions of the solute, such as the radiation-induced cis-trans isomerization of 2-butene in dodecane. We (1) J. W. F. van Ingen and W. A. Cramer, to be published in Trans. Faraday SOC. (2) R. B. Cundall and P. A. Griffiths, Discussions Faraday. Sac., 36, 111 (1963).
