Iridium

=Iridium= Iridium is found a precious metal found in group nine on the periodic table. It is very hard and brittle making it hard to work with. It is the most corrosive resistant metal know but it is attacked by molten salts. It is silvery white in color.

Color: white Harmful effects: Iridium is considered to be of low toxicity. Iridium in powder form is a known irrtitant and is a fire hazard. Characteristics: Iridium is a rare, hard, lustrous, brittle, very dense platinum-like metal. Chemically it is very unreactive. It is the most corrosion-resistant metal known and it resists attack by any acid. Iridium is attacked by molten salts such as sodium chloride (NaCl) and sodium cyanide (NaCN). Iridium is generally credited with being the second densest element (after [|osmium]) based on measured density, although calculations involving the space lattices of the elements show that iridium is denser.

Uses of Iridium
The main use of iridium is as a hardening agent for platinum alloys. With osmium, it forms an alloy that is used for tipping pens, and compass bearings. Iridium is used in making crucibles and other equipment that is used at high temperatures. It is also used to make heavy-duty electrical contacts. Iridium was used in making the international standard kilogram, which is an alloy of 90% platinum and 10% iridium. Radioactive isotopes of iridium are used in radiation therapy for the treatment of cancer

Idridium was discovered in 1803 and along with that there are only two naturally occuring isotopes of Iridium. It is found in the meteorites with an abundance much higher that its average abundance in the Earth's crust.
 * __Discovery:__**

Iridium compounds in use are the salts and acids it forms with chlorine. Iridium metals are used in spark pulgs, radioistope thermelectric genetors, and anything else that uses high heat.
 * __Uses:__**

Iridium and osmium were discovered at the same time by the British chemist Smithson Tennant in 1803. Iridium and osmium were identified in the black residue remaining after dissolving platinum ore with aqua regia, a mixture of 25% nitric acid (HNO3) and 75% hydrochloric acid (HCl). Today, iridium is still obtained from platinum ores and as a by-product of mining nickel. Pure iridium is very brittle and is nearly impossible to machine. It is primarily used as a hardening agent for platinum. Platinum-iridium alloys are used to make crucibles and other high temperature equipment. Iridium is also alloyed with osmium to make the tips of fountain pens and compass bearings. Iridium is the most corrosive resistant metal known. For this reason, the standard meter bar was created from an alloy of 90% platinum and 10% iridium. This bar was replaced as the definition of the meter in 1960 when the meter was redefined in terms of the orange-red spectral line of krypton-86. A thin, worldwide layer of iridium exists in a layer of sediment that was put down at the end of the Cretaceous period. Since meteors and asteroids contain a higher percentage of iridium than the earth's crust, this iridium enriched layer is seen as evidence that the earth was struck by a large meteor or asteroid at that time. Dust from the impact would have spread around the globe, depositing the iridium. The dust also would have blocked the sun for a time, resulting in the extinction of many plant and animal species, including the dinosaurs.
 * Atomic Number:** 77
 * Atomic Weight:** 192.217
 * Melting Point:** 2719 K (2446°C or 4435°F)
 * Boiling Point:** 4701 K (4428°C or 8002°F)
 * Density:** 22.42 grams per cubic centimeter
 * Phase at Room Temperature:** Solid
 * Element Classification:** Metal
 * Period Number:** 6 **Group Number:** 9 **Group Name:** none
 * What's in a name?** From the Latin word for rainbow, **iris**.
 * Say what?** Iridium is pronounced as **i-RID-ee-em**.
 * History and Uses:**
 * Estimated Crustal Abundance:** 1×10-3 milligrams per kilogram
 * Estimated Oceanic Abundance:** No Data Available
 * Number of Stable Isotopes:** 2 (View all isotope data)
 * Ionization Energy:** 9.1 eV
 * Oxidation States:** +4, +3




 * Symbol:** Ir **Atomic Number:** 77 **Atomic Mass:** 192.217 amu **Melting Point:** 2410.0 °C (2683.15 K, 4370.0 °F) **Boiling Point:** 4527.0 °C (4800.15 K, 8180.6 °F) **Number of Protons/Electrons:** 77 **Number of Neutrons:** 115 **Classification:** Transition Metal **Crystal Structure:** Cubic **Density @ 293 K:** 22.5 g/cm3 **Color:** white

Atomic Structure

 * [[image:http://www.chemicalelements.com/bohr/b0077.gif width="355" height="353"]] ||  || **Number of Energy Levels:** 6
 * First Energy Level:** **Second Energy Level:** **Third Energy Level:** **Fourth Energy Level:** **Fifth Energy Level:** **Sixth Energy Level:** ||

Isotopes

 * ** Isotope ** || ** Half Life ** ||
 * Ir-188 || 1.7 days ||
 * Ir-189 || 13.2 days ||
 * Ir-190 || 11.8 days ||
 * Ir-190m || 1.2 hours ||
 * Ir-190m2 || 3.2 hours ||
 * Ir-191 || Stable ||
 * Ir-192 || 73.8 days ||
 * Ir-193 || Stable ||
 * Ir-193m || 10.5 days ||
 * Ir-194 || 19.3 hours ||
 * Ir-194m || 170.0 days ||

Facts
Iridium has two naturally occurring, stable [|isotopes], 191Ir and 193Ir, with [|natural abundances] of 37.3% and 62.7%, respectively. [|[22]] At least 34 [|radioisotopes] have also been synthesized, ranging in [|mass number] from 164 to 199. [|192Ir], which falls between the two stable isotopes, is the most stable radioisotope, with a [|half-life] of 73.827 days, and finds application in [|brachytherapy] [|[23]] and in industrial [|radiography] , particularly for non-destructive testing of welds in steel in the oil and gas industries; iridium-192 sources have been responsible for a number of radiological accidents. Three other isotopes have half-lives of at least a day—188Ir, 189Ir, 190Ir. [|[22]] Isotopes with masses below 191 decay by some combination of [|β+ decay], [|α decay] , and [|proton emission] , with the exceptions of 189Ir, which decays by [|electron capture] , and 190Ir, which decays by [|positron emission]. Synthetic isotopes heavier than 191 decay by [|β− decay], although 192Ir also has a minor [|electron capture] decay path. [|[22]] All known isotopes of iridium were discovered between 1934 and 2001; the most recent is 171Ir. [|[24]] At least 32 [|metastable isomers] have been characterized, ranging in mass number from 164 to 197. The most stable of these is 192m2Ir, which decays by [|isomeric transition] with a half-life of 241 years, [|[22]] making it more stable than any of iridium's synthetic isotopes in their ground states. The least stable isomer is 190m3Ir with a half-life of only 2 µs. [|[22]] The isotope 191Ir was the first one of any element to be shown to present a [|Mössbauer effect]. This renders it useful for [|Mössbauer spectroscopy] for research in physics, chemistry, biochemistry, metallurgy, and mineralogy. [|[25]]
 * Date of Discovery:** 1804 **Discoverer:** S. Tenant **Name Origin:** From the Latin word //iridis// (rainbow) **Uses:** tip gold pens, crucible and special containers **Obtained From:** gravel deposits with platinum