Name molybdenum
Symbol Mo
Atomic Weight 95.94
Atomic Number 42
CAS ID 7439-98-7
Group Number 6
Group Name (none)
Period Number 5
Origin of Name Greek, molybdos = "lead"
Year Discovered 1781
Discovery Credits Isolated by P. J. Hjelm at Uppsala, Sweden
Class Metallic
Color Gray Metallic
Standard State Solid at 77 F & 298 K
Description Metal is lustrous, silvery, and fairly soft when pure. Usually obtained as gray powder. Used in alloys, electrodes, catalysts, and as the sulfide, lubricants.

Diagnostic tests: 
On charcoal molybdenum sulfide gives near the assay a copper-red stain in oxidizing flame and white oxide further away.
On plaster, mixed with KI, gives a deep ultramarine blue color after heating with the flame.
Bead tests using sodium phosphate (Na3PO4) gives a yellowish green color (hot) and nearly colorless (cold), the reducing flame color is a fine green.
Molybdates (MoO42-) are tested by adding powdered sample to a dry test tube with a scrap of paper, adding a few drops of water and an equal amount of concentrated H2SO4. The mixture is carefully heated until the acid fumes. Cool or slowly add water and the solution will assume a deep blue color.

Back to Elements Table Page