The noble metals are Cu, Ag, Au, Pt, Pd, sometimes Ir.
What about Ru and Ti? Aren't they noble metals as well?
Historically, the noble metals I suppose were "noble" because you had to be
a rich noble to afford to own any. It then took on the connotation of
non-reactive because Cu, Ag, Au, Pt, and Pd are frequently found as metallic
ores, rather than as oxides, sulfides or other compounds.
This whole concept has lost its meaning of "non-reactive" as modern
chemistry and metallurgy have discovered other elements such as Ru, Ti, Ta,
and others that are quite resistant to heat and chemical attack.
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Update: June 2012