Germanium
Atomic Data
| Atomic Number | 32 |
| Symbol | Ge |
| Atomic Weight | 72.63 u |
| Density (STP) | 5.323 g/cm³ |
| Melting Point | 938.25 °C (1211.4 K) |
| Boiling Point | 2832.85 °C (3106 K) |
| Electronegativity | 2.01 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p2 |
| Oxidation States | −4, +2, +4 |
| Phase at STP | Solid |
| Category | Metalloid |
| Period / Group | 4 / 14 |
| CAS Number | 7440-56-4 |
Electron Configuration
[Ar] 3d10 4s2 4p2
| 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 | 2 | 32 |
| Total | 32 | 32 | ||
Isotopes of Germanium
Germanium has five naturally occurring stable isotopes. The most abundant is ⁷⁴Ge, comprising 36.5% of all naturally occurring Germanium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Germanium-70 | ⁷⁰Ge | 32 | 38 | 20.57 | Stable |
| Germanium-72 | ⁷²Ge | 32 | 40 | 27.45 | Stable |
| Germanium-73 | ⁷³Ge | 32 | 41 | 7.75 | Stable |
| Germanium-74 | ⁷⁴Ge | 32 | 42 | 36.5 | Stable |
| Germanium-76 | ⁷⁶Ge | 32 | 44 | 7.73 | Stable |
Abundance & Occurrence
Germanium is present in Earth's crust at approximately 1.5 ppm by mass and at approximately 2 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
- Germanium dioxide dust: GeO2 dust is a mild irritant by inhalation; chronic high-level inhalation has caused kidney toxicity and peripheral neuropathy in industrial exposures: use respiratory protection when handling powders.
- Germane gas (GeH4): Germane is flammable, pyrophoric in some forms, and moderately toxic by inhalation; it is used in semiconductor deposition and requires gas detection, ventilation, and appropriate emergency procedures.
- Organo-germanium compounds: Certain organic germanium compounds have caused severe kidney failure when misused as dietary supplements; germanium compounds should never be ingested.
- General handling: Bulk germanium metal has low acute toxicity; standard metal handling precautions (dust mask, eye protection) are appropriate for cutting and polishing operations.
Germanium in the Real World
Real-World Uses
- Optical fibre cables: Germanium-doped silica glass has a higher refractive index than pure silica, forming the light-guiding core of optical fibres that carry internet and telecommunications signals around the world.
- Infrared optics: Germanium lenses and windows transmit the 8–14 μm thermal infrared wavelength band and are used in military and civilian thermal imaging cameras, night-vision systems, and gas-sensing instruments.
- Solar cells: Germanium substrates are used in multijunction III-V solar cells for space satellites, as the lattice constant of Ge closely matches that of GaAs, enabling efficient epitaxial growth of high-efficiency photovoltaic junctions.
- Catalysis in polymer production: Germanium dioxide is used as a catalyst in the production of polyethylene terephthalate (PET) plastic used in drink bottles and polyester fibres, particularly in East Asian manufacturing.
- Electronics and semiconductors: Germanium was the semiconductor in the first commercial transistors (1950s) and is now used in SiGe heterojunction bipolar transistors in high-frequency circuits and in advanced CMOS nodes where strained SiGe improves electron mobility.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is germanium used for?
Germanium is used primarily in fibre-optic cables and infrared optics: it transmits infrared light that glass does not, making it essential for thermal imaging cameras and night-vision equipment. Germanium is also used in gamma-ray detectors for nuclear medicine and security scanning, and historically was the material for the first transistors before silicon became dominant.
Is germanium toxic?
Germanium metal and most inorganic germanium compounds are considered to have low toxicity. However, certain organic germanium compounds and germanium dioxide taken as dietary supplements at high doses have been linked to serious kidney damage. Germanium is not an essential nutrient, and health claims about germanium supplements are not scientifically supported.
How was germanium discovered?
Germanium was discovered in 1886 by German chemist Clemens Winkler in the mineral argyrodite. Like gallium, its existence had been predicted by Mendeleev in 1871, who called it 'eka-silicon' and forecast many of its properties with remarkable accuracy. Winkler named it germanium in honour of his homeland Germany.
Why was germanium replaced by silicon in transistors?
Germanium transistors were the first type made in the late 1940s, but silicon quickly replaced them from the late 1950s onward. Silicon has a higher melting point, a larger bandgap (making it better at high temperatures), and its native oxide (SiO2) forms an ideal insulating gate layer. Silicon is also vastly more abundant and cheaper than germanium.