This week’s element is lovely osmium, which has the symbol Os and the atomic number 76.
Osmium is the rarest stable element in the Earth’s crust. It is a lustrous, blue-gray or blue-black transition metal in the platinum family. It is very hard and brittle, and has a very high melting point (the fourth highest of all the elements), making it difficult to work with. Osmium is the densest naturally occurring element (22.59 g/cm3 — slightly greater than iridium and twice that of lead). It is typically found in the wild either in its pure state or as an alloy, mostly in platinum ores.
This element was discovered in London in 1803 by Smithson Tennant and William Hyde Wollaston. Tennant obtained a black platinum material from silver mines in Colombia, which he reacted with sodium hydroxide at red heat. He obtained a yellow solution (probably cis–[Os(OH)2O4]2−) before distilling off volatile osmium tetroxide, OsO4. This, he named osmium (Greek osme translates as “a smell”) for its ashen and smoky smell.
Not only is osmium tetroxide volatile, but it is extremely toxic. However, it does have its uses. For example, it is used in electron microscopy to fix and stain tissue samples and, since it is electron dense, it enhances the image contrast thereby making cellular structures easier to see. Osmium tetroxide binds to fatty acids to form a black osmium dioxide residue and thus, is was once used to reveal fingerprints.
Osmium alloys are familiar to those who love fine fountain pens since the tip of these pens may be made from osmium alloyed with platinum, iridium, or other platinum group metals. Last century, osmium alloys were commonly used in phonograph styli until they were replaced by costlier but more durable diamond and sapphire stylus tips.
Osmium is perhaps most useful to scientists because 187Os is the beta-decay product of 187Re (half-life 4.56×1010 years). For this reason, rhenium-osmium dating is used determine the geologic age of rock. But, for this dinosaur fan, the most notable application of osmium dating is analysing the shocked quartz layer found at the Cretaceous–Paleogene boundary, when many dinosaurs became extinct 65 million years ago.
Here is our favourite professor, telling us a little more about osmium:
.. .. .. .. .. .. .. .. .. .. .. ..
Video journalist Brady Haran is the man with the camera and the University of Nottingham is the place with the chemists. You can follow Brady on twitter @periodicvideos and the University of Nottingham on twitter @UniofNottingham
You’ve already met these elements:
Rhenium: Re, atomic number 75
Tungsten: W, atomic number 74
Tantalum: Ta, atomic number 73
Hafnium: Hf, atomic number 72
Lutetium: Lu, atomic number 71
Ytterbium: Yb, atomic number 70
Thulium: Tm, atomic number 69
Erbium: Er, atomic number 68
Holmium: Ho, atomic number 67
Dysprosium: Dy, atomic number 66
Terbium: Tb, atomic number 65
Gadolinium: Gd, atomic number 64
Europium: Eu, atomic number 63
Samarium: Sm, atomic number 62
Promethium: Pm, atomic number 61
Neodymium: Nd, atomic number 60
Praseodymium: Pr, atomic number 59
Cerium: Ce, atomic number 58
Lanthanum: La, atomic number 57
Barium: Ba, atomic number 56
Cæsium: Cs, atomic number 55
Xenon: Xe, atomic number 54
Iodine: I, atomic number 53
Tellurium: Te, atomic number 52
Antimony: Sb, atomic number 51
Tin: Sn, atomic number 50
Indium: In, atomic number 49
Cadmium: Cd, atomic number 48
Silver: Ag, atomic number 47
Palladium: Pd, atomic number 46
Rhodium: Rh, atomic number 45
Ruthenium: Ru, atomic number 44
Technetium: Tc, atomic number 43
Molybdenum: Mo, atomic number 42
Niobium: Ni, atomic number 41
Zirconium: Zr, atomic number 40
Yttrium: Y, atomic number 39
Strontium: Sr, atomic number 38
Rubidium: Rr, atomic number 37
Krypton: Kr, atomic number 36
Bromine: Br, atomic number 35
Selenium: Se, atomic number 34
Arsenic: As, atomic number 33
Germanium: Ge, atomic number 32
Gallium: Ga, atomic number 31
Zinc: Zn, atomic number 30
Copper: Cu, atomic number 29
Nickel: Ni, atomic number 28
Cobalt: Co, atomic number 27
Iron: Fe, atomic number 26
Manganese: Mn, atomic number 25
Chromium: Cr, atomic number 24
Vanadium: V, atomic number 23
Titanium: Ti, atomic number 22
Scandium: Sc, atomic number 21
Calcium: Ca, atomic number 20
Potassium: K, atomic number 19
Argon: Ar, atomic number 18
Chlorine: Cl, atomic number 17
Sulfur: S, atomic number 16
Phosphorus: P, atomic number 15
Silicon: Si, atomic number 14
Aluminium: Al, atomic number 13
Magnesium: Mg, atomic number 12
Sodium: Na, atomic number 11
Neon: Ne, atomic number 10
Fluorine: F, atomic number 9
Oxygen: O, atomic number 8
Nitrogen: N, atomic number 7
Carbon: C, atomic number 6
Boron: B, atomic number 5
Beryllium: Be, atomic number 4
Lithium: Li, atomic number 3
Helium: He, atomic number 2
Hydrogen: H, atomic number 1
Here’s the Royal Society of Chemistry’s interactive Periodic Table of the Elements that is just really really fun to play with!
.. .. .. .. .. .. .. .. .. .. ..
Follow Grrlscientist’s work on facebook, Google +, LinkedIn, Pinterest and of course, twitter: @GrrlScientist
email: grrlscientist@gmail.com