Periodic table › Indium
1. Identity and classification
Soft, ductile, silvery-white metallic solid with relatively low melting point compared to d-block transition metals
- Name and symbol
- Indium (Indium) · In
- Atomic number
- 49
- Relative atomic weight / mass number
- 114.82 ± 0.01
- Group · period · block
- 13 · 5 · p
- Category
- Post-transition Metal
- State near room temperature
- Solid
- Stable isotopes
- At least one stable isotope
- CAS number
- 7440-74-6
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 49 · 49
- Neutrons in reference isotope
- 66 (115In)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p¹- Abbreviated configuration
[Kr]5s² 4d¹⁰ 5p¹- Electrons per shell
- 2, 8, 18, 18, 3
- Listed oxidation states
- +3
- Electronegativity
- 1.78 (Pauling)
- First ionization energy
- 558.264 kJ/mol · 5.786 eV
- Electron affinity
- 28.946 kJ/mol
- Covalent radius
- 142 pm
- van der Waals radius
- 193 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 7.31 g/cm³
- Melting point
- 429.75 K · 156.6 °C · 313.88 °F
- Boiling point
- 2345 K · 2071.85 °C · 3761.33 °F
- Crystal structure
- Tetragonal
- Specific heat
- 0.233 J/(g·K)
- Thermal conductivity
- 81.8 W/(m·K)
- Enthalpy of fusion
- 3.281 kJ/mol
- Enthalpy of vaporization
- 231.8 kJ/mol
- Magnetic ordering
- Diamagnetic
- Mohs hardness
- 1.2
- Speed of sound
- 1215 m/s
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The listed electron configuration and oxidation states describe atomic structure; compound properties depend on bonding and composition.
Selected compounds: InO / In₂O₃ (Oxide) · InClₙ (Chloride) · InFₙ (Fluoride)
Reaction reference
Oxidation behavior depends on temperature, surface passivation and the chemical environment.
Direct reaction with water is element- and condition-dependent.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 113In | Stable | 4.281% | Stable |
| 115In | Radioactive | 95.719% | 4.41E+14 Y |
| 116In | Radioactive | — | 14.10 s |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1863 CE
- Scientists associated with discovery
- Ferdinand Reich & Hieronymous Theodor Richter
- Location
- Germany (Freiberg)
- Origin
- Natural
- Listed crustal abundance
- Not established
Minerals and naming reference
Trace in Sphalerite (ZnS) and Chalcopyrite ores
Named from scientific/historical roots associated with Indium (In), discovered or characterized by Ferdinand Reich & Hieronymous Theodor Richter.
7. Applications
Indium Tin Oxide (ITO) transparent conductive touchscreens (smartphones, LCD/OLED TVs), low-melting solders, InGaN LEDs
Detailed applications by field
- everyday
- Indium Tin Oxide (ITO) transparent conductive touchscreens (smartphones, LCD/OLED TVs), low-melting solders, InGaN LEDs
- industry
- Used in post-transition metal processing, specialized alloys, and chemical manufacturing (Indium Tin Oxide (ITO) transparent conductive touchscreens (smartphones, LCD/OLED TVs), low-melting solders, InGaN LEDs).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Indium's electronic structure ([Kr] 4d¹⁰ 5s² 5p¹) provides target conductivity.
- medicine
- Diagnostic imaging, biomedical instrumentation, or pharmaceutical synthesis research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Indium.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Indium.
- agriculture
- Soil geochemistry analysis, trace micronutrient research, or analytical environmental monitoring.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 5 p-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as non-essential in human and biological systems.