WebElements: Helium - Extensive information on history, uses, occurrence, and properties of the element. It's Elemental: Helium - Basic physical and historical information. ChemicalElements.com: Helium - Basic information, atomic structure, and table of isotopes. Especiál Gas Inc.: Helium - Numeric data, uses, and general information. USGS Minerals Information: Helium - Statistics and information on the worldwide supply, demand, and flow of the element (PDF format). Corrosionsource.com: Helium - History, sources, properties, isotopes, and uses. EnvironmentalChemistry.com: Helium - Atomic structure, chemical and physical properties, and table of nuclides. Lenntech: Helium - Physical data, chemical properties, and health effects. Wikipedia: Helium - Properties of the element, including its history, applications, and characteristics.