Xenon hexafluoroplatinate

From Free net encyclopedia

Xenon hexafluoroplatinate was the first noble gas compound to be prepared. It was prepared by Neil Bartlett in 1962, giving proof that noble gases can be used to form molecules. Its formula is Xe⁺[PtF₆]⁻.

Contents 1 Description 2 History 3 Preparation 4 References

Description

Xenon hexafluoroplatinate is a mustard yellow solid. It was the first compound prepared containing a noble gas. Noble gases are elements which do not easily participate in chemical bonding because their valence electron shells are filled. For the heavier noble gases such as xenon, the outer electrons are more shielded from electronic interactions with the nucleus. These less tightly bound outer electrons have been found to participate in chemical bonding. Template:Ref

This compound is ionic. It may consist of an octahedral anionic fluoride complex of platinum and a monovalent cation of xenon.Template:Ref But it has been proposed that the platinum fluoride structure is a negatively charged polymeric network with xenon or xenon fluoride cations held in its meshes. A preparation of XePtF₆ in HF solution results in a solid which has been characterized as a [PtF₅^-]_n polymeric network associated with XeF⁺. This result is evidence for such a polymeric structure of xenon hexafluoroplatinate.Template:Ref

History

The existence of noble gases was not known until after the advent of the periodic table. In the late nineteenth century, Lord Rayleigh discovered that some samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions. He and William Ramsay theorized that the nitrogen extracted from air was associated with another gas, argon. With this discovery, they realized that a whole class of gases was missing from the periodic table. Eventually all the known noble gases were discovered and the table was completed.

Noble gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are normally the only electrons which can participate in chemical bonding. According to atomic theory derived from quantum mechanics and experimental trends, atoms with full valence electron shells are extraordinarily stable and therefore do not form chemical bonds. But Linus Pauling suggested that some noble gas compounds could be made, although they would violate the octet rule.Template:Ref In 1962, Neil Bartlett discovered that a sample of platinum hexafluoride gas kept overnight became a red solid. The red solid turned out to be dioxygenyl hexachloroplatinate, O₂[PtF_{6], in which an electron has been removed from the oxygen molecule by the platinum hexafluoride molecule. Bartlett later compared the ionization energies needed for removal of the first electron from an oxygen molecule and a xenon atom, and found that the energies required were similar. Then he asked his colleagues to give him some xenon "so that he could try out some reactions", and he successfully synthesized xenon hexafluoroplatinate, the first known compound containing a noble gas.Template:Ref}

Preparation

Xenon hexafluoroplatinate is prepared by mixing Xe and PtF₆ as gaseous solutions in SF₆. The reaction is optimally performed at 77K and slowly warmed to let remaining reactants slowly react to completion. It has been shown though that this preparation leads to the formation of XeF⁺ PtF₆⁻ and other compounds, especially when any excess of PtF₆ is present.Template:Ref

References

1. Template:Note Chemical Heritage foundation (2006). "William Ramsay".
2. Template:Note The American Chemical Society "molecule of the week" (2006). "Xenon Hexafluoroplatinate"
3. Template:Note Gerber, R.B.(2001). Annual Review of Physical Chemistry 55, 55-78.
4. Template:Note Graham, L.; Graudejus, O.; Jha N.K.; Bartlett, N.(2000). Coordination Chemistry Reviews 197, 321-334.