Quick Facts
| Property | Value |
|---|---|
| Symbol | In |
| Atomic Number | 49 |
| Atomic Mass | 114.82 u |
| Category | Post-Transition Metal |
| Period | 5 |
| Group | 13 |
| Block | p |
| Electron Configuration | [Kr] 4d¹⁰ 5s² 5p¹ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 7.31 g/cm³ |
| Melting Point | 156.60°C (429.75 K) |
| Boiling Point | 2072°C (2345 K) |
| Appearance | Silvery-white, very soft metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Kr] 4d¹⁰ 5s² 5p¹ |
| Electronegativity | 1.78 (Pauling scale) |
| First Ionization Energy | 558.3 kJ/mol |
| Atomic Radius | 167 pm |
| Covalent Radius | 142 pm |
| Van der Waals Radius | 193 pm |
History and Discovery
Discovered by: Ferdinand Reich and Hieronymous Theodor Richter Year of Discovery: 1863 Location: Freiberg, Germany
Etymology
Named from the Latin "indicum" meaning "indigo," due to the bright indigo-blue spectral line used to identify it.
Discovery Story
Ferdinand Reich discovered indium in 1863 while testing zinc ores for thallium using spectroscopy. Reich was colorblind and asked Hieronymous Richter to confirm the observation. Richter saw a bright indigo spectral line that identified a new element.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ¹¹³In | 4.29% | Stable | - |
| ¹¹⁵In | 95.71% | 4.4 × 10¹⁴ years | β⁻ |
Occurrence
Natural Abundance
Indium is rare, comprising about 0.1 ppm of Earth's crust. It does not form its own ores but is found in zinc, lead, and copper ores. Major producers are China, South Korea, and Japan.
Extraction and Production
- Byproduct: Primarily from zinc refining
- Electrolytic: Recovered from zinc electrolysis residues
- Sources: Zinc smelting operations
- Global production: about 900 tons annually
Applications and Uses
Electronics
- Indium tin oxide (ITO) for touchscreens and LCD displays
- Transparent conductive coatings
- Semiconductors (InP, InGaAs)
- LEDs
Solders and Alloys
- Low-melting alloys
- Lead-free solders
- Fusible alloys
- Dental alloys
Photovoltaics
- CIGS (copper-indium-gallium-selenide) solar cells
- Thin-film solar panels
Other Uses
- Bearings (indium coating)
- Cryogenic seals
- Nuclear reactor control rods
Biological Role
Indium has no known biological role and is not essential for any organism.
In the Human Body
Indium is not normally present in the body. Trace amounts may be absorbed from food.
Toxicity
Limited toxicity data; indium compounds are considered mildly toxic.
Safety and Hazards
Toxicity
Indium has low toxicity. Indium tin oxide dust may be hazardous. Indium compounds can cause lung disease with chronic industrial exposure.
Handling Precautions
- ITO dust may cause lung disease (indium lung)
- Standard metal handling procedures
- Use ventilation when producing dust
- Avoid inhalation of indium compounds
Environmental Impact
Indium is rare and production is tied to zinc refining. Electronic waste containing indium is a growing concern.
Interesting Facts
- Indium is soft enough to scratch with a fingernail
- It makes a high-pitched "scream" when bent (like tin)
- Demand for indium has surged with the growth of touchscreens
- Indium wets glass, making it useful for sealing
- About 70% of indium goes into ITO for flat-panel displays