Ytterbium

ChemicalElements.com: Ytterbium - Basic information, atomic structure, and isotopes.
http://www.chemicalelements.com/elements/yb.html

Visual Elements: Ytterbium - Image, physical information, and ionisation energies.
http://www.chemsoc.org/viselements/pages/ytterbium.html

LANL: Ytterbium - History, sources, properties, and uses.
http://periodic.lanl.gov/elements/70.html

ChemGlobe: Ytterbium - Electronic, thermal, and steric data along with an isotope table.
http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/70.html

WebElements: Ytterbium - Extensive information on history, uses, occurrence, compounds, and properties.
http://www.webelements.com/webelements/elements/text/Yb/key.html

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

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

It's Elemental: Ytterbium - Basic physical and historical information.
http://education.jlab.org/itselemental/ele070.html

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