Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

For more information on the Visual Elements image see the Uses and properties section below.



A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).

Atomic number
The number of protons in an atom.

Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.

Melting point
The temperature at which the solid–liquid phase change occurs.

Boiling point
The temperature at which the liquid–gas phase change occurs.

The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

Density (g cm−3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.

Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.

Atoms of the same element with different numbers of neutrons.

CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.

Fact box

Group 13  Melting point 156.60°C, 313.88°F, 429.75 K 
Period Boiling point 2027°C, 3681°F, 2300 K 
Block Density (g cm−3) 7.31 
Atomic number 49  Relative atomic mass 114.818  
State at 20°C Solid  Key isotopes 115In 
Electron configuration [Kr] 4d105s25p1  CAS number 7440-74-6 
ChemSpider ID 4514408 ChemSpider is a free chemical structure database


Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


The description of the element in its natural form.

Biological role

The role of the element in humans, animals and plants.

Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

Image explanation
The symbol used here is the Japanese kanji character ‘hon’. It means ‘origin’. Indium is named after the bright indigo line in its spectrum. The Japanese discovered that cotton was a difficult fabric to dye, except with indigo. So, indigo dye was widely used to colour cotton throughout the Edo period (1603–1867).
A soft, silvery metal that is stable in air and water.
Most indium is used to make indium tin oxide (ITO), which is an important part of touch screens, flatscreen TVs and solar panels. This is because it conducts electricity, bonds strongly to glass and is transparent.

Indium nitride, phosphide and antimonide are semiconductors used in transistors and microchips.

Indium metal sticks to glass and can be used to give a mirror finish to windows of tall buildings, and as a protective film on welders’ goggles. It has also been used to coat ball bearings in Formula 1 racing cars because of its low friction.

An indium alloy has been used for fire-sprinkler systems in shops and warehouses because of its low melting point.
Biological role
Indium has no known biological role. It is toxic if more than a few milligrams are consumed and can affect the development of an embryo or foetus.
Natural abundance
Indium is one of the least abundant minerals on Earth. It has been found uncombined in nature, but typically it is found associated with zinc minerals and iron, lead and copper ores. It is commercially produced as a by-product of zinc refining.
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Indium was discovered in 1863 by Ferdinand Reich at the Freiberg School of Mines in Germany. Reich was investigating a sample of the mineral zinc blende (now known as sphalerite, ZnS) which he believed might contain the recently discovered element thallium. From it he obtained a yellow precipitate which he thought was thallium sulfide, but his atomic spectroscope showed lines that were not those of thallium. However, because he was colour-blind he asked Hieronymous Richter to look at the spectrum, and he noted a brilliant violet line, and this eventually gave rise to the name indium, from the Latin word indicum meaning violet.

Working together Reich and Richter isolated a small sample of the new element and announced its discovery. Subsequently the two men fell out when Reich learned that when Richter, on a visit to Paris, claimed he was the discover.

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.

Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.

Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.

Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.

First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

Atomic radius, non-bonded (Å) 1.93 Covalent radius (Å) 1.42
Electron affinity (kJ mol−1) 28.9 Electronegativity
(Pauling scale)
Ionisation energies
(kJ mol−1)


Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Atoms of the same element with different numbers of neutrons.

Key for isotopes

Half life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Oxidation states and isotopes

Common oxidation states 3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  115In 114.904 95.71 4.4 x 1014 β- 


Data for this section been provided by the British Geological Survey.

Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.

Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.

Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact

Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.

Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.

Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.

Supply risk

Relative supply risk 7.6
Crustal abundance (ppm) 0.052
Recycling rate (%) <10
Substitutability Low
Production concentration (%) 53
Reserve distribution (%) Unknown
Top 3 producers
  • 1) China
  • 2) Republic of Korea
  • 3) Japan
Top 3 reserve holders
  • Unknown
Political stability of top producer 24.1
Political stability of top reserve holder Unknown


Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.

Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

Specific heat capacity
(J kg−1 K−1)
233 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- 8.31
x 10-11
x 10-5
0.0127 1.413 40.9 - - - - -
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Listen to Indium Podcast
Transcript :

Chemistry in its element: indium


You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

(End promo)

Meera Senthilingam

This week, the rare, lustrous element that we have to thank for our flat screen TVs and computer monitors. To tell us more about the chemistry of indium here's Claire Carmalt.

Claire Carmalt

Until 1924 a gram or so constituted the world's supply of indium in its isolated form. Today around 480 tonnes are produced annually from mining and a further 650 tonnes annually from recycling. So why all the need for indium and what are the unique properties of it that makes it a much sought after element?

Indium is relatively rare with its abundance in the Earth's crust estimated to be around 0.1 parts per million. Hence it is slightly more abundant than silver or mercury. Indium is generally found in ores of zinc and is produced mainly from residues generated during zinc ore processing. Indium is a moderately toxic metal by inhalation and mildly toxic by ingestion. However, the exact nature of its human toxicity is not clearly understood.

Indium is a soft, malleable metal with a brilliant lustre. The name indium originates from the indigo blue it shows in a spectroscope. Indium has a low melting point for metals and above its melting point it ignites burning with a violet flame. Bizarrely, the pure metal of indium is described as giving a high-pitched "cry" when bent. This is similar to the sound made by tin or the 'tin cry", however, neither of them is really much like a cry!

It has the unusual property of remaining soft and workable at very low temperatures. This property allows it to be used in special equipment needed for temperatures near absolute zero. It is an excellent choice for cryogenic pumps, high vacuum systems and other unique joining and sealing applications. Indium lends itself to this application due to its ability to conform to many irregular surfaces and its characteristic "stickiness". Indeed, when pure, it sticks very tightly to itself or to other metals. This property makes it useful as a solder - it reduces the melting point of some solders, strengthens others, and prevents some solders from breaking down too easily. For example, when used as a washer between a silicon diode or other temperature sensors and refrigerator cold stages, indium foil increases the thermal contact area and prevents the sensor from detaching due to vibration. Other uses of indium are in the manufacture of batteries and electronic devices, and in research.

Another important use of indium is in making alloys - used in electronic devices and dental materials. Indium has been called a "metal vitamin" in alloys, which means that very small amounts of indium can make big changes in an alloy. For instance, the addition of small amounts of indium to gold and platinum alloys makes them much harder. Some aircraft parts are made of alloys that contain indium and it prevents them from reacting with oxygen in the air or wearing out.

Indium metal dissolves in acids, but does not react with oxygen at room temperature. However, at higher temperatures, it combines with oxygen to form indium oxide. It is in this form that indium finds application as a transparent conductive oxide. As the name indicates these materials, when applied as a thin coating onto glass or plastic films, are both transparent to visible light as well as electrically conductive. It is actually Indium Tin Oxide or "ITO" which is used and this is one of the most important applications of indium.

About 45% of all indium is used to make ITO and this finds application in solar cells and flat panel displays (LCDs - liquid crystal displays). For both of these applications the ITO is used to establish an electric current over the device and to pass light through it. When architectural or photovoltaic glass is coated with ITO it keeps the harmful infrared rays of the sun from passing through. If coated onto aircraft or automotive windshields, it allows the glass to be electrically deiced or demisted as well as reducing the air conditioning requirement by reducing heat gain. Other compounds of indium used in solar cells include indium gallium arsenide and copper indium gallium selenide. Many scientists think that solar cells may replace natural gas, coal and oil for many applications in the future. However, the availability of indium has been questioned since the demand has risen rapidly in recent years with the popularity of LCD televisions and computer monitors. On the free indium market, this has lead to considerable price increases and the unavailability of sizeable quantities of indium. Currently, increased recycling and manufacturing efficiency maintain a good balance between demand and supply.

Meera Senthilingam

So, an element with a multitude of uses, varying from solar cells and windscreen demisters to LCD screens, batteries and even dental materials. No wonder we need to recycle it to meet the element's demand. That was University College London's Claire Carmalt with the chemistry and uses of indium. Now next week an element that changed the rules of nature.

Eric Scerri

Until the early 1960s it was believed that three bonds between any two atoms was as high as Nature could go, as in the case of the nitrogen-nitrogen triple bond for example. But in 1964 Albert Cotton and co-workers in the USA discovered the existence of a metal-metal quadruple bond. Yes you guessed it, it as rhenium!

Meera Senthilingam

Join UCLA's Eric Scerri to find out what other surprises rhenium has in store in next weeks Chemistry in its element. Until then I'm Meera Senthilingam from the Naked and thank for listening.


Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by There's more information and other episodes of Chemistry in its element on our website at

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Visual Elements images and videos
© Murray Robertson 1998-2017.



W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.


Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.


Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.


History text

Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.



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