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Indium

physical science Maturity 7-9 Next article →

Indium is a silvery-white post-transition metal with the chemical symbol In and atomic number 49. It is one of the softest known elements in the periodic table. Because of its unique physical and chemical properties, indium is vital for modern technology. It helps create the screens we use for computers and phones. It also plays a major role in the semiconductor industry. Without this metal, many of our electronic devices would not function as they do today.

Physically, indium is highly ductile, meaning it can be stretched into thin wires without breaking.

Indium wire
Indium wire

It is incredibly soft, with a Mohs hardness of only 1.2. You can actually cut indium with a knife. If you rub it on paper, it leaves a visible line much like a pencil. A strange phenomenon occurs when you bend the metal. It produces a high-pitched crackling sound. This sound is caused by a process called crystal twinning.

Indium wetting glass
Indium wetting glass

Indium also has the ability to wet glass, a property it shares with gallium.

Indium belongs to group 13 on the periodic table. Its properties are largely intermediate between its neighbors, gallium and thallium. This means its characteristics often fall between the two. For example, indium has a melting point of 156.60 °C (313.88 °F). This temperature is higher than gallium but lower than thallium. Its density is 7.31 g/cm3, which is also between the two neighbors. Below a critical temperature of 3.41 K, indium becomes a superconductor. This means it can conduct electricity with zero resistance.

In 1863, German chemists Ferdinand Reich and Hieronymous Theodor Richter discovered indium. They were studying ores from mines in Saxony, Germany. They used a method called spectroscopy to examine the light emitted by these minerals. Reich was color-blind, so he relied on Richter to identify colored spectral lines. They were originally searching for the green lines of thallium. Instead, they discovered a bright indigo blue line. They named the element indium after this color. The name comes from the Latin word *indicum*, which refers to indigo.

Indium wire
Indium wire

Indium is used extensively in the production of flat-panel displays. It is a key component of indium tin oxide, or ITO. ITO is a transparent and conductive coating applied to glass. This allows the glass to carry an electric current while remaining clear.

Dell axim LCD under microscope
Dell axim LCD under microscope

This technology is essential for the screens in smartphones and televisions. Indium is also used to make blue and white LED circuits. It is used to produce indium gallium nitride p-type semiconductor substrates. These substrates are necessary for the light-emitting diodes used in modern lighting.

Indium is not usually mined on its own. It is produced as a by-product during the processing of other metals. Most indium comes from zinc sulfide ores, such as sphalerite. In space, indium is created through a process called the s-process, or slow neutron capture. This occurs in low-to-medium-mass stars.

S-process-elem-Ag-to-Sb
S-process-elem-Ag-to-Sb

In this process, atoms like silver-109 capture neutrons over thousands of years. Through a series of steps and beta decays, they eventually become indium-115. This explains why indium-115 is the most abundant isotope on Earth, making up 95.7% of all indium.

Chemically, indium is quite versatile. It most commonly donates three electrons to become indium(III). However, it can also form indium(I) compounds due to the inert pair effect. This effect happens because relativistic effects lower the energy of the 5s-orbital. Indium is also known for its solubility in mercury. It has a greater solubility in liquid mercury than any other metal. In the laboratory, indium(III) compounds like indium chloride are common.

Kristallstruktur Chrom(III)-chlorid
Kristallstruktur Chrom(III)-chlorid

These compounds are often used as Lewis acids in chemical reactions.

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🖼️ Images & Media (5)
File:Indium wetting glass.jpg
Indium wetting glass.jpg
File:Kristallstruktur Chrom(III)-chlorid.png
Kristallstruktur Chrom(III)-chlorid.png
File:S-process-elem-Ag-to-Sb.svg
S-process-elem-Ag-to-Sb.svg
File:Dell axim LCD under microscope.jpg
Dell axim LCD under microscope.jpg
File:Indium wire.jpg
Indium wire.jpg
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