PTL:Osmium

From ChemEd Collaborative

Osmium is a transition metal in the iron subgroup of Group VIIIB (Group 8) and the 6th period. Other members of the group are iron (Fe) and ruthenium (Ru). It is one of the six platinum group elements: ruthenium, osmium (Os), rhodium (Rh), iridium (Ir), palladium (Pd), and platinum (Pt).

1 Discovered
2 Name
3 Characteristics
4 Uses
5 Emission Spectra

Discovered

The element was discovered, along with iridium, in 1803 by S. Tennant in the black residue left after dissolving crude platinum in aqua regia.

Name

He named the element after the Latin word for "odor" because of the characteristic and pungent odor of the volatile oxide, OsO4. (NOTE: This oxide is very toxic.)

Characteristics

Osmium is exceedingly rare in the earth's crust (0.005 ppm), but 50 times more abundant than its neighbor ruthenium. (Note the contrast between these abundances and that of iron, the other member of this subgroup.) As a consequence, Os is an expensive element, costing about $7200 per 100 grams (in 1991), a price that makes it one of the most expensive elements. Like rhodium and iridium, osmium is a by-product of the nickel processing industry.

In the solid state, the metal has a hexagonal closest packed structure.

Os has oxidation numbers ranging from 0 to 8, but it is usually +3, +4, +6, or +8 in its compounds.

Although iridium is thought to be the densest known substance (22.65 g/cc), the density of osmium is only slightly less (22.61 g/cc).

The metal is bluish white, extremely hard but brittle, and difficult to fabricate. It is attacked by air at high temperatures to give toxic OsO₄.

Uses

Osmium is used in fountain pen tips, phonograph needles, and in instrument bearings such as the one in the compass above

Osmium is used almost entirely to make very hard alloys with other platinum group metals to make [fountain pen tips, instrument bearings, phonograph needles], and electrical contacts.