What is Iridium

Iridium (pronounced as i-RID-ee-em) is a hard and brittle metal represented by the chemical symbol Ir. It is the least reactive element, belonging to the platinum family. It has 34 isotopes with mass numbers ranging from 165 to 198 of which only Ir-191 and Ir-193 exist naturally with a stable half-life ^{[1, 2]}.

Where is Iridium Found on Earth

It is one of the rarest elements found in an uncombined form in sediment deposits of river. Also, it is commercially obtained as a byproduct of nickel refining ^[1].

History

Origin of its Name: Its name is derived from Iris, the Greek goddess of the rainbow ^[1].

Who Discovered it: Smithson Tennant ^[1]

When and Where was Iridium Discovered

In 1803, Tennant dissolved crude platinum in dilute aqua regia to obtain a black residue of graphite. After treating with alkalis and acids alternately, he was able to obtain two new elements of which one was named iridium and the other osmium at the Royal Institution, London.

Later in 1813, Humphry Davy, the Cornish chemist, and his team tried to melt the new metal using high power current generated by large batteries ^[1].

Identification
Atomic number	77 [1]
CAS number	7439-88-5 [1]
Position in the periodic table [1]	Group	Period	Block
	9	6	d

Classification, Properties and Characteristics of Iridium

General Properties
Relative atomic mass	192.217 [1]
Atomic mass/weight	192.217 atomic mass units [8]
Molar mass	192.217 g/mole [9]
Mass Number	192
Physical Properties
Color/appearance	Silver [1]
Melting point/freezing point	2446°C (4435°F) [1]
Boiling point	4428°C (8002°F) [1]
Density	22.56 g/cm3 [1]
Standard state at room temperature (solid/liquid/gas)	Solid [1]
Magnetic Properties
Magnetic type		Paramagnetic [1]
Molar magnetic susceptibility		3.21×10-10 m3/mol
Mass magnetic susceptibility		1.67×10-9 m3/kg
Volume magnetic susceptibility		0.0000377
Chemical Properties
Oxidation state/Oxidation number			(−3), −1, +1, +2, +3, +4, +5, +6 [1]

Atomic Data of Iridium (Element 77)

What is Iridium Used for

• Since Ir is resistant to corrosion, it’s mixed with osmium to produce alloys used in pen tips and compass bearings. Standard meter bars, crucibles and spark plug contacts prepared from a mixture of 10% iridium and 90% platinum have a high melting point and low reactivity ^{[1, 2]}.
• Iridium-192, a radioactive isotope of the metal, is a potential therapy for prostate cancer ^[5].
• Ir implants can be used in the radiotherapy of breast cancer ^[6].
• Iridium combined with platinum have been made into electrodes that may the potential to manage hearing impairment.

Does the Element Have any Toxic Effects

Although the metallic element has low toxicity, accidental eye or skin contact with some of its compounds cause severe irritation. In some animal studies, its inhalation and ingestion has been shown to cause respiratory and abdominal issues ^[7].

Interesting Facts

• The thin layer of the element present in the earth’s crust is a result of a large meteor with a high percentage of Ir that had hit the earth at the end of Cretaceous period ^[1]

Iridium Price

The cost of the pure metal is anywhere between $ and $ per gram.

References
1. http://www.rsc.org/periodic-table/element/77/iridium
2. https://education.jlab.org/itselemental/ele077.html
3. https://pubchem.ncbi.nlm.nih.gov/compound/iridium#section=Top
4. http://periodic.lanl.gov/77.shtml
5. https://www.ncbi.nlm.nih.gov/pubmed/1877110
6. https://www.ncbi.nlm.nih.gov/pubmed/1827719
7. https://www.iloencyclopaedia.org/part-ix-21851/metals-chemical-properties-and-toxicity/item/140-iridium
8. http://hobart.k12.in.us/ksms/PeriodicTable/iridium.htm
9. https://www.webqc.org/molecular-weight-of-iridium.html
10. http://chemistry-reference.com/q_elements.asp?Symbol=Ir