{"id":128,"date":"2020-04-08T15:07:13","date_gmt":"2020-04-08T15:07:13","guid":{"rendered":"https:\/\/thechemicalelements.com\/?page_id=128"},"modified":"2023-08-16T08:33:07","modified_gmt":"2023-08-16T08:33:07","slug":"iridium","status":"publish","type":"post","link":"https:\/\/thechemicalelements.com\/iridium\/","title":{"rendered":"Iridium (Ir)"},"content":{"rendered":"\n

Iridium is a chemical element with atomic number 77 in the periodic table. In Earth\u2019s crust, this precious metal occurs in scarce amounts. As a member of the platinum<\/a> family of periodic table elements, iridium is characterized by a high density and hardness. It has nine valence electrons that can occur in the oxidation states +1, +3, and +4. <\/span><\/p>\n\n\n\n

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Chemical and Physical Properties of Iridium<\/span><\/h3>\n\n\n\n
Property<\/strong><\/td>Value<\/strong><\/td><\/tr>
Symbol<\/td>Ir<\/td><\/tr>
Name<\/td>Iridium<\/td><\/tr>
Atomic number<\/td>77<\/td><\/tr>
Atomic weight<\/td>192.22 g.mol-1<\/td><\/tr>
Group<\/td>Transition Metal<\/a><\/td><\/tr>
Period<\/td>6<\/td><\/tr>
Color<\/td>A lustrous, silver-white metal with a yellowish hue<\/td><\/tr>
Physical state<\/td>Solid at room temperature<\/td><\/tr>
Electronegativity<\/td>2.2<\/td><\/tr>
Density<\/td>22.42 g.cm-3 at 20\u00b0C<\/td><\/tr>
Melting point<\/td>2450\u00b0C<\/td><\/tr>
Boiling point<\/td>4527\u00b0C<\/td><\/tr>
Ionic radius<\/td>0.066 nm (+4)<\/td><\/tr>
Van der Waals radius<\/td>0.126 nm<\/td><\/tr>
Isotopes<\/td>11<\/td><\/tr>
Most characteristic isotope<\/td>192Ir<\/td><\/tr>
Electronic shell<\/td>[Xe] 4f14 5d7 6s2<\/td><\/tr>
The energy of the first ionization<\/td>886 kJ.mol-1<\/td><\/tr>
Shells<\/td>2,8,18,32,15,2<\/td><\/tr>
Crystal Structure<\/td>Cubic: Face centered<\/td><\/tr>
Covalent Radius<\/td>1.27 \u00c5<\/td><\/tr>
Atomic Radius<\/td>1.87 \u00c5<\/td><\/tr>
Atomic Volume<\/td>08.54 cm\u00b3\/mol<\/td><\/tr>
Name Origin<\/td>Latin: iris (rainbow)<\/td><\/tr>
Discoverer<\/td>S.Tenant, A.F.Fourcory, L.N.Vauquelin, H.V.Collet-Descoltils<\/td><\/tr>
Year<\/td>1804<\/td><\/tr>
Location<\/td>England\/France<\/td><\/tr>
Pronunciation<\/td>i-RID-i-em<\/td><\/tr>
Oxidation States<\/td>2,3,(4),6<\/td><\/tr>
Uses<\/td>Used with osmium to tip gold pen points, to make crucible and special containers, and in heat-resistant alloys<\/td><\/tr>
Description<\/td>Rare, very heavy, soft, silvery-white metal<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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Located between osmium<\/a> and platinum in the periodic table, the chemical element iridium is labeled with the symbol Ir and the atomic number 77. It has an atomic mass of 192.2 g.mol<\/span>-1<\/span> and electron configuration [Xe] 4f<\/span>14<\/span> 5d<\/span>7<\/span> 6s<\/span>2<\/span>. Iridium is the hardest substance according to the classification of elements within Mendeleev\u2019s system. <\/span><\/p>\n\n\n\n

This member of the platinum family is also very brittle and dense in its metal form. However, when exposed to temperatures between 1,200\u00b0 and 1,500\u00b0 C (2,200\u00b0 to 2,700\u00b0 F), iridium becomes ductile and malleable. Iridium reaches a boiling point at 4527\u00b0C, while its melting point is at 2450\u00b0C. <\/span><\/p>\n\n\n\n

Iridium has a specific gravity of 22.42 (17\u00b0C), an electronegativity of 2.2 according to Pauling, and the atomic radius according to van der Waals is 0.126 nm. Its crystal structure is cubic-face centered. Being non-reactive with water, acids, silicates, molten metals, or air, this transition metal is able to resist corrosion better than any other metal in the periodic table of elements. Iridium is unaffected even by <\/span>aqua regia<\/span><\/i>. Ruthenium<\/a> and osmium are the only elements that show lower reactivity than iridium.  <\/span><\/p>\n\n\n\n

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How Was Iridium Discovered?<\/span><\/h2>\n\n\n\n

Ancient Ethiopians and various peoples from the South American continent were familiar with a type of platinum ore that contained traces of several chemical elements that are classified in the platinum family of the periodic table, such as ruthenium, rhodium<\/a>, palladium<\/a>, osmium, and iridium. <\/span><\/p>\n\n\n\n

In the 17th century, this ore was introduced in Europe by the Spanish conquistadors, who had learned about – what was locally referred to as <\/span>platina<\/span><\/i> or “silverette” – on their South American exploits on the territory of today\u2019s western Colombia.<\/span><\/p>\n\n\n\n

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Smithson Tennant and the Discovery of Iridium<\/span><\/h3>\n\n\n\n

The story of iridium’s discovery takes place in London in the year 1803. The English chemist Smithson Tennant (1761 \u2013 1815) made a revolutionary discovery of two new chemical elements – iridium (Ir) and osmium (Os) – by conducting a chemical analysis on the acid-insoluble black residues from these platinum ore solutions. <\/span><\/p>\n\n\n\n

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The 300-Pound Cape of Good Hope Iron Meteorite <\/span><\/h3>\n\n\n\n

Prior to this, Tennant\u2019s curiosity was sparked by the analysis of a 300-pound Cape of Good Hope iron<\/a> <\/span>meteorite<\/span><\/a> in 1801. In the meteorite analysis he conducted, Tennant exposed the sample to acid which resulted in graphite (plumbago). <\/span><\/p>\n\n\n\n

In 1803, Tennant attempted an individual experiment on a crude platinum sample. By diluting it in aqua regia, the British scientist obtained black residue from the platinum ore solution. Since he previously managed to isolate graphite during the meteorite experiment, Tennant disagreed with his French colleague Joseph Louis Proust (1754 \u2013 1826) who thought that the black residue from the platinum ore submerged in aqua regia was graphite, i.e. the crystalline form of carbon<\/a>. In order to prove his claim, Tennant exposed the solution to alkalis and marine (hydrochloric) acid and purified the platinum ore, which helped him isolate two new chemicals – iridium and osmium. <\/span><\/p>\n\n\n\n

On June 21, 1804, Tennant submitted his scientific evidence in a letter addressed to the Royal Society of London for Improving Natural Knowledge (today\u2019s Royal Society) after which the new element iridium was officially recognized and assigned the atomic number 77 in the periodic table. <\/span><\/p>\n\n\n\n

It should be noted that the French chemists H.V. Collet-Descotils, A.F. Fourcroy, and N.L. Vauquelin attempted performing similar experiments to Tennant\u2019s. However, they failed in isolating iridium from the platinum ore solution residue. <\/span><\/p>\n\n\n\n

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Robert Hare\u2019s Contribution<\/span><\/h3>\n\n\n\n

Robert Hare (1781 \u2013 1858), an American chemist and professor of chemistry at the University of Pennsylvania, is considered to be the first scientist who managed to distill iridium in its pure form. <\/span><\/p>\n\n\n\n

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How Did Iridium Get Its Name?<\/span><\/h2>\n\n\n\n

The name of this chemical element was inspired by the Greek goddess of the rainbow, Iris (also derived from the Latin word for rainbow, \u2018<\/span>iris<\/span><\/i>\u2019). The British chemist Smithson Tennant, who was a professor at Cambridge, gave the name <\/span>iridium<\/span><\/i> to his newly discovered element in 1804 after finding a striking resemblance of the vivid colors of the salts that were produced under bright lights with the colors of the rainbow. <\/span><\/p>\n\n\n\n

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Where Can You Find Iridium?<\/span><\/h2>\n\n\n\n

In the Universe, a large percent of iridium occurs in meteors and asteroids. In fact, they contain larger amounts of the 77th element than Earth\u2019s crust. The sediment in the layers that do contain some iridium are traced to the end of the <\/span>Cretaceous period<\/span><\/a>. <\/span><\/p>\n\n\n\n

In fact, some scientists believe that during the <\/span>asteroid impact<\/span> <\/a>which led to the extinction of the dinosaurs, element 77 was disseminated throughout our planet along with an incredible amount of climate-changing gases that were released into the atmosphere upon impact. In this way, iridium was deposited into the alluvium formations. The very thin layer of iridium in Earth’s crust that dates from the Cretaceous period is considered to be <\/span>evidence<\/span><\/a> of a collision between Earth and an asteroid. <\/span><\/p>\n\n\n\n

In the alluvial iridium deposits of the Earth\u2019s thinnest layer (i.e. its crust), this chemical element may either occur in its free elemental form or compounded with platinum or other noble metals that share similar chemical properties (like the iridium-osmium alloy, i.e.osmiridium). <\/span><\/p>\n\n\n\n

For commercial use, iridium is obtained as a by-product in the mining of nickel<\/a> (sulfides), platinum, copper<\/a>, and nickel ores. Brazil, Australia, the United States, Myanmar, Russia, and South Africa are where the world\u2019s largest iridium ore mines are located. <\/span><\/p>\n\n\n\n

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Iridium in Everyday Life<\/span><\/h2>\n\n\n\n

The pure, elemental form of iridium metal is not easy to be worked with due to its hardness and brittleness. That\u2019s why this substance is mainly used in platinum alloys, which are used for various applications in different industries, in medicine, and in scientific research:<\/span><\/p>\n\n\n\n