• Helium has a full outer shell of two electrons.
  • The other gases have full outer shells of two  and six  electrons.
  • Compounds have been formed with Rn, Xe, Kr, and Ar.
  • The first compound (XePtF6) was made with xenon in 1962.
  • Radon also will give a reddish glow, but is not used because it is radioactive and will not retain its structure as radon for any significant length of time.
  • Only helium and neon have not formed compounds at this time.
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