John H. Holloway
The University of Aberdeen Aberdeen, Scotland
I
I
The Photochemical Reaction of Xenon
I
A demonsfration of the reactivity of xenon
with Fluorine at Room Temperature
T h e new-found chen~istryof the noble gases has, during the last few years, provided a new solme of interest for chemists everywhere. The chemistry is limited to the elements krypton, xenon? and radon (1). There is no evidence of reactivity in other nohle gases. In the case of krypton and radon, knowledge is limited to observations on only a few compounds. The chemistry of xenon is also restricted because, although xenon has been s h o ~ nto exhibit even valcncies from I1 to VIII, these have been detected only in stable fluorides and their complexes, aqueous species obtained by the hydrolysis of these fluorides, and two unstable oxides (2). From a practical point of vie~v, most fluorine chemistry is technically difficult and hazardous (3). Until the publication of recent papers by workers at the Research Institute of Temple University (4) and ourselves @), the methods reported for the preparation of compounds of xenon have been somewhat elaborate (2). Although it is impossible to remove the difficulties and hazards inherent in the handling of fluorine, our new method is simple, and an adaption of it. provides a useful demonstration of the reactivity of xenon. When mixtures of xenon and fluorine in Pyrex bulbs at room temperature and atmospheric pressure are subjected to diffuse daylight or bright sunlight xenon fluorides are formed (4,5). The nature of the fluoride produced depends on the ratio of fluorine to xenon in the bulb. Bulbs in which there is more xenon than is required for a reaction represented by the equation Xe + Fz XeF?
-
yield xenon difluoride as the only xenon containing species (4, 5). In experiments where fluorine is present in a larger excess than is necessary for the reaction Xe
+ 2F.
-
XeF4
the results are more complex Experiments in these laboratories have shown that, although xenon tetrafluoride is produced, it is not the singular inevitable product of the reaction and a closer investigation is necessary. S o formation of xenon fluorides occurs when bulbs containing Xe/F2 mixtures are kept in darkness, which shows that the reactions must. be photochemical. (These same mixtures, after exposure to daylight, have deposited visible crystals after only 24 hours). The photochemistry of the formation of xenon difluoride from xenon and fluorine has already been studi d by Weeks and Matheson (6, 7). Their light source was a 1000-W high pressure mercury arc. Their quan202 / Journal of Chemical Education
tum yields were of the order of 0.3-0.7. Approximate calculations by L. V. Streng and A. G. Streng (4) on a similar system to ours using ordinary daylight showed that the formation of XeFz could he completely accounted for by a photochemical reaction between Xe and Fz with a quantum yield of about unity. XeFz Preparation and Analysis
A series of experiments was made (Table 1). The same experimental procedure was adopted in each case. APyrex bulb of known volume (Figure 1)was evacuated until a "hard" vacuum was obtained. All traces of moisture were removed by flaming the bulb thoroughly with a large blow-torch. The drying process was continued for three days. A known volunle of dry xenon was admitted, and the bulb was drawn off at A (Fig. 1). Dry, hydrogen fluoride-free fluorine was admitted to the bulb through a greaseless (Teflon diaphragm) valve or a I O r m poru>ds," The Cniw~.sityof Chici~goh . e q C l ~ i w s ra d Lnndon. 1963. n. S!I.
The Demonstration Experiment
A d~n~onstration experiment to illustrate the reactivity of xmon to flnorine can easily bc executed if thc pure, dry gasrs arc available. A suitable apparatus is shown in Figure 2. Two 250 ml. or 500 ml. Pyrex glass bulhs are joined via a breakseal. A few nickel billls arc placed in one bulb and are held in placc by a magnct taped to the outsidc of the bulh. The bulhs are evacuated and flamed out simultancously through stop-corks B and C, (Fig. 2) located on the sides of tllc bulhs. Fluorine is introduced into one bulb and xenon into the ot,her. Thc stop-cocks are closed. Thc apparatus is then ready for use.
Volume 43, Number 4, April 1966
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