6 links
ChemicalElements.com: Radon
chemicalelements.com
Basic information, atomic structure, and table of isotopes.
EnvironmentalChemistry.com: Radon
environmentalchemistry.com
Atomic structure, properties, and table of nuclides.
WebElements: Radon
ebelements.com
Extensive information on history, uses, occurrence, and properties.
Wikipedia: Radon
en.wikipedia.org
Properties of the element, including its history, applications, and characteristics.