ChemGlobe: Sodium
- Electronic, thermal, and steric data along with basic information.
- http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/11.html

LANL: Sodium
- Sources, properties, uses, and compounds.
- http://periodic.lanl.gov/elements/11.html

Wikipedia: Sodium
- Properties of the element, including its history, applications, and characteristics.
- http://en.wikipedia.org/wiki/Sodium

Lenntech: Sodium
- Physical data, chemical properties, health and environmental effects.
- http://www.lenntech.com/Periodic-chart-elements/Na-en.htm

EnvironmentalChemistry.com: Sodium
- Atomic structure, chemical and physical properties, and table of nuclides.
- http://environmentalchemistry.com/yogi/periodic/Na.html

ChemicalElements.com: Sodium
- Basic information, atomic structure, and table of isotopes.
- http://www.chemicalelements.com/elements/na.html

It's Elemental: Sodium
- Basic physical and historical information.
- http://education.jlab.org/itselemental/ele011.html

Radiochemistry of Sodium
- Full text of the monograph by W. T. Mullins and G. W. Leddicotte (Oak Ridge National Laboratory, Oak Ridge, Tennessee). [PDF]
- http://lib-www.lanl.gov/cgi-bin/getfile?rc000010.pdf

Visual Elements: Sodium
- Image, animation, source, uses, key isotopes, and ionisation energies.
- http://www.chemsoc.org/viselements/pages/sodium.html