For a long time, scientists believed that you could not make covalent compounds using Noble Gas, Group 18, elements because they are just not reactive. All these elements have a full valence shell of electrons (s2p6 for all the Noble Gases except helium, which has no p electrons) so there is no tendency to gain or lose electrons.
In 1933, Linus Pauling used his new concept of electronegativity, the power of an atom to attract electrons, to predict the possibility of making compounds using the heavier Noble Gas elements and fluorine or oxygen.
Fluorine, with an an electronegativity of 4.0 is the most electronegative element in the Periodic Table, so atoms of fluorine have the greatest power to attract electrons. Oxygen is the second most electrongetative element with an electronegativity of 3.5. So, if you want to try to make a compound with an "unreactive" non-metal like a Noble Gas, you should probably use a reactive non-metallic element like fluorine or oxygen.
Now, as you go down any Group of the Periodic Table from top to bottom, the electrons in the highest energy levels (the valence electrons) are less strongly attracted to the nucleus because they are further away from the nucleus. So, if you want your "unreactive" Noble Gas atom to share electrons with your more reactive fluorine or oxygen atom, you will want to use a Noble Gas from the bottom of the Group, that is, xenon or radon.
So why didn't Linus Pauling predict radon compounds instead of xenon compounds then?
Radon is a radioactive element which occurs naturally as the nuclear decay product of uranium or thorium.
The real problem, as far as the production of radon compounds is concerned, is that its most stable isotope, radon-222, has a half-life of just 3.8 days, not much time for the preparation, isolation, and structural determination of your new compounds!
Xenon, on the other hand, occurs in the Earth's atmosphere in trace amounts, about 0.09 ppm (by volume) and naturally occurring xenon includes 8 stable isotopes.
In June 1962, Neil Bartlett reported that xenon reacted with platinum hexafluoride to produce xenon compounds ( a mixture of XeFPtF6 and XeFPt2F11).
In September 1962, Howard Claasen reported the production of XeF4 by reacting xenon and fluorine at high temperature.
XeF2 can actually be produced simply by exposing xenon and fluorine gases to sunlight !
Many xenon compounds have now been synthesized, and many of these compounds include the electronegative elements fluorine and/or oxygen.
Suggested Study Questions
- Write the electron configuration for each of the following elements:
- the largest atomic number
- the largest number of electrons in an atom
- the largest atomic radius
- the lowest first ionization energy
- the lowest electronegativity