Indium

What is Indium?

Indium is a post-transition metal that is soft, malleable, and silvery gray. It is so soft that it can be cut with a knife. It is commonly used to lower the melting point of alloys, to add transparent coating on glass that conducts electricity, and LCD displays.

Indium’s Place in the Periodic Table

Indium is a post-transition metal in group 13 and period 6. Post-transition metals are located between transition metals (Cu, Ag, Hg, Cn) to the left on the periodic table and metalloids (B, Si, As, Ge, Sb, Te) to the right. It has a low melting point that is than gallium but lower than thallium. Similarly, its density is intermediate between gallium and thallium.

• Atomic number: 49
• Atomic Radius:  167 picometers
• Atomic mass: 114.82
• Symbol: In
• Group: 13
• Period: 5
• Number of Protons: 49
• Number of Electrons: 49
• Number of Neutrons: ~66
• Number of Isotopes: 2 natural isotopes

Properties of Indium

Indium is a soft metal with a low melting point. When it is bent by physical force, a high-pitched sound is emitted. This is a property shared by tin and is a result of disrupting the ordered crystal structure of the element Contrary to the intermediate properties with neighboring elements in group 13, indium has a boiling point that is higher than thallium but lower than gallium.  At low temperatures (-269 °C), indium becomes a superconductor. Superconductors conduct electricity with very little resistance. most commonly forms compounds with +3 oxidation states. Indium is susceptible to corrosion at high temperatures but this can be limited if isolated from air and humidity. It does not pass through tissues easily but can be toxic if injected into the blood stream.

Physical Properties

Indium is solid at room temperature and has a density similar to tin and promethium. It melts at 156.6 °C, which is close to the temperature of a match head when ignited. It has a boiling point close to that of manganese at 2072 °C.

• Melting Point: 156.6 °C.
• Boiling Point: 2072 °C.
• Density of Solid Indium: 31 g cm^-3.
• Phase at Room Temperature: solid

Chemical Properties

Indium has 3 valence electrons, two in the 5s orbital and 1 in the 5p orbital. It is most stable in chemical compounds when it donates three electrons, which would lead to a more stable valence shell with 10 electrons. Atoms with larger numbers of electrons in their valence shells are more stable. This is This is known as electrostatic attraction. Indium does not react with water but can react with strong oxidizing agents such as halides.

• Oxidation states: -5, -2, -1, +2, +3
• Specific Heat: .23 J g^-1K^-1
• Electronegativity: 1.78 (Pauling scale)
• Heat of Fusion: 281 kj mol^-1
• Heat of Vaporization: 231.8 kj mol^-1
• Electron Configuration: [Kr] 4d¹⁰5s² 5p¹

Isotopes

Indium has two naturally occurring isotopes, . These isotopes are known as primordial nuclides, which means that they were generated during the Big Bang, 13.8 billion years ago. Indium-113 is the only stable isotope and makes up 95% of indium. Indium-115 is radioactive but is still present in the universe because it has a half-life 1000-times longer than the age of the universe. Indium-115 and indium-113 are not purified from each other for specific applications, so materials that contain indium have a mixture of both proportional to their abundance in nature. 39 other synthetic isotopes exist, and their mass numbers range from 97 to 135. Of these, indium-111 is the most stable with a half-life of 2.8 days.

Alloys and Allotropes

To confer the properties of softness and low melting temperature, indium is added to alloys that contain bismuth, cadmium, lead and tin. These alloys have melting temperatures between 50 and 100 °C. Alloys that contain gallium, indium, and tin are called Galinstan, and are liquid at room temperature. Such alloys may be used as alternative thermometers that use mercury, which is also liquid at room temperature but is much more toxic.

Compounds of Indium

Indium tin oxide (ITO) is used to cover glass for a number of applications, including prevents condensation. Because ITO also conducts electricity, ITO coatings can be used to transmit electrical signals on touch screens, flat screen televisions, and solar panels.

Interesting Facts about Indium

• Indium is said to “scream” when bent. This is similar to the tin “cry.”
• Pure indium costs about $1000 per 100 grams.
• An alloy of 24% indium and 76% gallium has a melting point of 16 °C, which is well below room temperature.
• Indium is less susceptible to corrosion than other metals like iron. Therefore, one of its first uses was to coat metal bearings of high performance aircrafts used in World War II. However, it is no longer used for this purpose, as better corrosion-resistant materials have been developed.

Occurrence and Abundance of Indium

Indium was produced during the big bang, and is constantly generated by nuclear fusion in stars. It makes up about 3×10^-8 % of the universe, which is more abundant than uranium but less abundant that gold and silver. On Earth, indium is the 68th most abundant element, and has a similar abundance to silver, bismuth, and mercury. It is rarely found in its elemental form on Earth. However, it’s a byproduct of zinc production as it is present in sphalerite mineral deposits, which contain zinc, iron and sulfur. Sphalerite deposits can be around continental Europe, Russia, Canada, the United States, Mexico, and Peru.

Uses of Indium

Most Notable Uses in General

Indium compounds are used for a variety of common applications. It is used in street lights to reflect infrared light back to the light bulb, which is useful because the light bulb works most efficiently at high temperatures. With a low melting temperature, indium is also useful to solder metal components together. Liquid indium can be used to produce mirrors when poured on the surface of glass.

Most Notable Uses in Science

Have you filled cavities at the dentist? Indium is used in to reduce the amount of mercury required in metal fillings. Glass covered with indium compounds create a transparent layer that conducts electricity.

Discovery of Indium

Indium was discovered by Ferdinand Reich and Hieronymous Theodor Richter in Germany in 1863. They were analyzing the elements present in common minerals. A common method to identify elements is by emission spectra, or the production of light. When elements are heated, electrons are excited to higher energy levels. When they fall back down to their base energy level, they emit various colors of light. Indium is named after one of the colors that it emits when heated – indigo.

Indium in the Future

With advances in the use of LCD monitors on common electronic devices, the demand for indium is expected to increase. It is estimated that within 20 years, sources of indium may be depleted. Scientists are researching how indium coatings can be recycled from disposed electronic devices. Researchers are also looking to expand the use of indium to improve lithium ion batteries by increasing their lithium storage capacity.