What are the properties electron configuration oxidation states and uses of iridium
What is Iridium?
Iridium is a rare and dense transition metal with atomic number 77. It belongs to the platinum family and is denoted by the symbol Ir. The Ir element is generally hard and brittle; still, it can become ductile at a very high temperature around 1200 to 1500 oC. It is one of the rarest elements in the earth with an annual production of only 3 tonnes. This element doesn't occur in nature in pure form. Iridium is one of the densest metals found in nature with a density of about 22.56g/cm3.
Iridium Properties
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The above image shows the Iridium metal in pure form
Discovery
When the chemists dissolved platinum in aqua regia to study its properties, they observed a small amount of insoluble residue, which is dark in color. Some thought that it is graphite, while others cannot make any conclusion. In 1803, a British scientist Smithson Tennant concluded that this residue is any new metal after analyzing it properly. He conducted various experiments and found that the salts that he obtained with this metal were strongly colored. Hence, he named it iridium after the Greek winged goddess of rainbow Iris.
Natural Occurrence
Iridium is one of the rarest metals on the earth due to its less abundance. Even the platinum metal is ten times more abundant than the Ir element. However, scientists believe that it has a higher concentration in the earth's core because of its siderophile (iron-loving) character. Generally, this element is present in nature in the form of natural alloys. In all the platinum group metal, iridium is present naturally in alloys with raw copper or nickel. Very few minerals in the earth's crust contain this element in the dominant form. Some of the rare examples are cuproiridsite and irarsite.
Iridium is present in the earth's crust in higher concentrations in three kinds of structure. They are impact craters, igneous deposits, and deposits reworked. The most popular primary reserves of iridium on earth are Sudbury basin, Norilsk in Russia, Bushveld igneous complex in South Africa, etc.
Physical Properties of Iridium
Iridium is a member of platinum group metal and hence resembles the characteristics of platinum in many ways. It is white but with a slight yellowish shade. It is hard, brittle, and has a very high melting point as compared to other metals. Hence, it is not easy to work with this transition metal. The boiling point of iridium is 4428°C, the tenth highest among all the elements. At the temperature below 0.14K, this element becomes a superconductor.
The density of iridium is 22.56g/cm3, which makes it the densest metal after osmium. The modulus of elasticity of this metal is also very high as compared to other elements. Moreover, it has a very low Poisson's ratio along with high shear modulus. All these Iridium properties make it resistant to deformation.
Chemical Properties of Iridium
Among all the known metals, Ir is one of the most corrosion-resistant elements found in nature. Even the harshest of acids like hydrochloric acid, sulfuric, and aqua regia does not affect this element. Silicates or molten metals at high temperatures cannot attack iridium. Very few molten salts and halogens at a high temperature can attack iridium. It can react with sulfur to form iridium disulfide at atmospheric pressure.
Ir element can form compounds in several oxidation states from -3 to +9. However, the most common ones are +3 and +4. The only well-characterized oxide of this transition metal is IrO2. It is a blue-black solid which can react with HNO3 to give Ir2O3. Iridium can also form iridates like K2IrO3 and KIrO3 after reacting with potassium oxide at high temperatures. Ir can react with halides, but it cannot create any mono-halides or dihalides. It can react with almost every halogen to yield trihalides. However, it can also react with fluoride to give tetrafluoride, pentafluoride at the desired conditions.
Iridium generally forms very few complexes. The complexes of this element have octahedral molecular geometry and are diamagnetic. In Organo-iridium compounds, the element is present in lower oxidation states. For example, Ir4(CO)12 is one of the most stable binary carbonyls of this metal in which Ir has the oxidation state zero.
Isotopes
Two naturally occurring isotopes of Ir are 191Ir and 193Ir. Today, there are around 37 known radioisotopes of this metal, ranging from mass number 164 to 202. The most stable known radioisotope of this transition metal is 192Ir, which has a half-life of approx 73.82 days. This isotope has many applications in industrial radiography and other industries. It is beneficial for testing welds in steel in gas and oil industries without any destruction. The scientists discovered all the isotopes of this element between the years 1934 to 2003. No isotope of iridium was found after 2008.
FAQs on Iridium Chemical Element Properties and Applications
1. What is iridium?
Iridium is a chemical element with the symbol Ir and atomic number 77, known for being one of the densest and most corrosion-resistant metals.
- It belongs to the platinum group metals (PGMs).
- It is a hard, brittle, silvery-white transition metal.
- Iridium is extremely resistant to heat and chemical attack, including acids.
- It occurs naturally in platinum ores and is very rare in Earth’s crust.
2. What is the electron configuration of iridium?
The electron configuration of iridium (Ir) is [Xe] 4f14 5d7 6s2.
- Atomic number: 77 (77 electrons in a neutral atom).
- It is a d-block transition element.
- The 5d and 6s electrons participate in metallic bonding and oxidation states.
3. What are the common oxidation states of iridium?
The most common oxidation states of iridium are +3 and +4, although it can range from −3 to +9.
- +3: Common in coordination complexes such as IrCl3.
- +4: Found in iridium(IV) oxide, IrO2.
- Higher oxidation states (e.g., +6) occur in fluorides like IrF6.
4. Why is iridium so corrosion resistant?
Iridium is highly corrosion resistant because it has a very stable metallic structure and forms protective surface oxides.
- It is resistant to most acids, including aqua regia.
- It does not oxidize easily at room temperature.
- Its strong metallic bonding and high density reduce chemical reactivity.
5. What are the physical properties of iridium?
Iridium is a dense, hard, brittle, silvery-white transition metal with a very high melting point.
- Atomic number: 77
- Atomic mass: 192.22 g·mol−1
- Density: 22.56 g·cm−3 (among the highest of all elements)
- Melting point: 2446 °C
- Boiling point: 4428 °C
6. How is iridium extracted from its ores?
Iridium is extracted as a by-product during the refining of platinum and nickel ores.
- Platinum ores are dissolved in aqua regia (a mixture of HCl and HNO3).
- Less reactive metals like iridium remain as insoluble residues.
- Further chemical separation and reduction processes isolate pure iridium metal.
7. What is iridium dioxide (IrO2)?
Iridium dioxide is a stable oxide of iridium with the formula IrO2, where iridium is in the +4 oxidation state.
- It is a dark, crystalline solid.
- It has a rutile-type crystal structure.
- It is used as an electrocatalyst in water oxidation reactions.
8. What are the uses of iridium in chemistry and industry?
Iridium is used in high-temperature equipment, electrical contacts, and as a catalyst due to its strength and corrosion resistance.
- Crucibles for growing single crystals at high temperatures.
- Spark plugs because of its high melting point and durability.
- Catalysts in organic reactions and electrochemical processes.
- Hardening agent in platinum alloys.
9. What is the difference between iridium and platinum?
Iridium is denser and more corrosion resistant than platinum, while platinum is more malleable and easier to work with.
- Iridium (Ir): Density ≈ 22.56 g·cm−3, very brittle.
- Platinum (Pt): Density ≈ 21.45 g·cm−3, highly malleable and ductile.
- Both belong to the platinum group metals.
10. Why is iridium associated with the dinosaur extinction?
Iridium is associated with the dinosaur extinction because a high concentration of iridium was found in the Cretaceous–Paleogene (K–Pg) boundary layer.
- Iridium is rare in Earth’s crust but more common in meteorites.
- The global iridium-rich clay layer suggests a large asteroid impact.
- This evidence supports the impact hypothesis for the mass extinction event 66 million years ago.
