Osmium

Osmium is a dense, brittle, bluish-white transition metal with atomic number 76. It is used in hard alloys and, as osmium tetroxide, in laboratory staining and chemical reactions.

Periodic table: A tabular arrangement of chemical elements ordered by atomic number and recurring chemical properties. Osmium’s group and period place it among the transition metals and reveal its nearest elemental relatives.
Crystal structure: The orderly three-dimensional arrangement of atoms in a crystalline solid. Osmium’s hexagonal close-packed structure helps determine its density and mechanical behavior.
Electron microscopy: Imaging techniques that use beams of electrons to reveal structures at very small scales. Osmium compounds can improve contrast in biological specimens prepared for electron microscopy.
Iridium: A hard, corrosion-resistant transition metal with atomic number 77 and a member of the platinum-group metals. Iridium’s density is close to osmium’s, and their ranking depends on measurement conditions.
Smithson Tennant: An English chemist who discovered osmium and iridium in 1803. Tennant identified osmium while investigating residues from dissolving crude platinum.
Transition metal: An element whose atoms have an incompletely filled d subshell or form cations with an incomplete d subshell. Osmium’s d-electron chemistry gives it metallic bonding and several accessible oxidation states.
Metallic bonding: Chemical bonding in metals, in which valence electrons are shared across an extended lattice. Delocalized electrons bind osmium atoms into a conductive metallic solid.
Biological staining: The use of dyes or reactive compounds to make biological structures distinguishable under imaging. Osmium tetroxide stains lipid-rich membranes and preserves them for microscopy.
Rhodium: A silvery, corrosion-resistant transition metal with atomic number 45 and a member of the platinum-group metals. Rhodium provides a less dense platinum-group comparison with extensive catalytic uses.
Platinum: A dense, malleable, corrosion-resistant transition metal with atomic number 78. Osmium was discovered in the insoluble residue left during purification of native platinum.

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