P i w 4 r*r New England Associa+ion of C h e n ~ @ ~ h e ~ ~ %,w
Roland Ward University of Connecticut Storrs
I
I
Would Mendeleev Have Predicted the Existence of XeF4?
The astonislime~~t with which most of us inorganic chcmists received the news of the isolatioo of xenon tetrafluoride (1) marked the event as a first rank accomplishment of the practical chemist. The preparation of this compound and other fluorides of the noble gases has been carried out in many laboratories in recent months. Some of them have been found to be remarkably stable. When one recovers from the first surprise of these events, a vague feeling of guilt begins to grow in one's consciousness. Should one have suspected the existence of such compounds? Would a present day Mendeleev-indoctrinated with the notions of electronic orbitals-have been able to predict the existence and shape of these molecules? I think the answer is yes! We have been accustomed to thinking of the periods of the periodic table beginning with group I and ending with the inert gas group. Our freshmen have been taught that the atoms of the noble gases are inert because tlie eight outer electrons form a stable group. This seems to bring tlie period to a definite end in a neat and logical way. We list the fluoridcs of the elements in which the central atoms can be regarded as having eight electrons (forming tetrahedral molrculcs including unshared electron pairs) using sp3 hybrid orbitals. The compound OF2, for example, could be regarded as a tetrahedral molecule as illustrated in Figure 1 (the angle 17-0-F is 103.2O). F F + F:C:F
:N:F
:O:F
.. .. :F:F .. ..
:Ne:
..
+
:Pu's:
..
SF2has been reported (2) hut not substantiated. Brl' is unstable with respect to the reaction: 3 BrF
-
Br?
+ BrF*
The inferelme might hc made that the piglit electroll configuration is not very attractive for seleuimn, tellurium, or iodine and possibly not for xenon and radon Let us now consider the sequences of fluorine compounds with the centsal atom sharing teu elert,ronspresumably using sp3d orbitals and having the trigonal bipyraniid orientation of liga~idslike thc planar chlorine trifluoride molecule (1:i~urr 2). .1list of these is given in Tahle 2.
Figure 2
Table 1 .
SiFl GeFl SnF4 PbF*
Octet Compounds, Atoms and Ions
PFI &Fa SbF
...
(SF*)
.. .
...
...
CIF BrF"
-
...
Ar Iir Se Hn
I
., J . Am. Chem. Suc., 79,3686 (1957).
Volume 40, Number 5, Moy 1963
1 279
