Indium
Atomic Data
| Atomic Number | 49 |
| Symbol | In |
| Atomic Weight | 114.82 u |
| Density (STP) | 7.31 g/cm³ |
| Melting Point | 156.6 °C (429.75 K) |
| Boiling Point | 2071.85 °C (2345 K) |
| Electronegativity | 1.78 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p1 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Post-Transition Metal |
| Period / Group | 5 / 13 |
| CAS Number | 7440-74-6 |
Electron Configuration
[Kr] 4d10 5s2 5p1
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| O | 5 | 5s | 2 | 48 |
| O | 5 | 5p | 1 | 49 |
| Total | 49 | 49 | ||
Isotopes of Indium
Indium has two naturally occurring stable isotopes. The most abundant is ¹¹⁵In, comprising 95.71% of all naturally occurring Indium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Indium-113 | ¹¹³In | 49 | 64 | 4.29 | Stable |
| Indium-115 | ¹¹⁵In | 49 | 66 | 95.71 | Stable |
Abundance & Occurrence
Indium is present in Earth's crust at approximately 0.25 ppm by mass and at approximately 3 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Skin and eye irritation: Indium metal and indium compounds cause mild skin and eye irritation; fine metal dust should not be inhaled.
- Indium lung: Occupational exposure to indium-tin oxide (ITO) dust: used in flat-panel displays: has caused severe, potentially fatal interstitial lung disease ('indium lung'); grinding or sputtering ITO requires stringent respiratory controls and medical surveillance.
- Systemic toxicity: Soluble indium salts are moderately toxic by injection in animal studies; they affect the liver, kidney, and bone marrow; human systemic toxicity from occupational routes is primarily from ITO dust inhalation.
- Gallium-indium alloys: Room-temperature liquid gallium-indium alloys wet most surfaces and can embrittle aluminium and other structural metals on contact; handle with appropriate containment.
Indium in the Real World
Real-World Uses
- Transparent conductive coatings (ITO): Indium tin oxide (ITO) is sputtered onto glass and plastic to form the transparent electrode in touchscreens, LCD displays, OLEDs, and solar cells, where it must be both electrically conductive and optically transparent.
- Semiconductor devices: Indium phosphide (InP) and indium gallium arsenide (InGaAs) are III-V semiconductors used in high-frequency transistors for fibre-optic communication lasers, photodetectors, and microwave circuit amplifiers.
- CIGS solar cells: Copper indium gallium selenide (CIGS) thin-film photovoltaic modules contain indium as a key constituent of the light-absorbing semiconductor, offering flexible, lightweight solar panels for building-integrated applications.
- Low-melting soldering alloys: Indium-containing solders (In-Sn, In-Bi, In-Ag) have melting points below 120 °C and are used to attach heat-sensitive components, bond cryogenic joints, and seal glass-to-metal vacuum systems.
- Bearing coatings: Thin indium plating on copper-lead and silver bearings improves corrosion resistance and conformability in high-load aircraft and diesel engine applications.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is indium used for?
Indium's dominant use is in indium tin oxide (ITO), a transparent electrical conductor used as the electrode layer in LCD screens, touchscreens, and flat-panel displays. Virtually every smartphone, tablet, and monitor contains ITO. Indium is also used in low-melting alloys, solders, and as a bearing metal coating. Indium phosphide and indium gallium arsenide are used in high-speed transistors and fibre-optic laser diodes.
Is indium toxic?
Indium is not considered highly toxic at low exposures. However, indium compounds: particularly indium tin oxide dust inhaled occupationally: have been linked to serious pulmonary disease including indium lung (pulmonary alveolar proteinosis), documented in workers at ITO manufacturing plants. As with many metal compounds, occupational inhalation exposure should be minimised.
How was indium discovered?
Indium was discovered in 1863 by German chemists Ferdinand Reich and Hieronymus Theodor Richter using spectroscopy. While examining zinc ore samples for thallium, they found a brilliant indigo-blue spectral line belonging to a new element. Richter later isolated the metal. The name indium comes directly from that distinctive indigo spectral line.
Is indium supply a concern for display technology?
Yes, indium is considered a critical raw material in many countries because it is relatively scarce and mostly recovered as a byproduct of zinc mining. There is no primary indium mining: almost all comes from processing zinc ores. Growing demand for displays and photovoltaics has driven research into ITO alternatives such as graphene, silver nanowires, and conducting polymers, but ITO remains dominant because of its combination of transparency, conductivity, and processability.