Germanium

Germanium is a shiny grey metalloid that was predicted by Mendeleev in 1871 and discovered exactly as described in 1886. For decades it was at the heart of the electronics revolution as the material for the first transistors, until silicon took over. Today it is critical for infrared optics, optical fibre cables and high-efficiency solar cells.

  • Atomic Number3232 protons, 32 electrons
  • Atomic Mass72.63 uAbout 73× heavier than hydrogen
  • State at Room TempSolidgrey-white metalloid
  • Density5.323 g/cm³About 5× denser than water
  • Melting / Boiling938.3°C / 2832.8°CMelts at 938°C
  • Discovered1886Clemens Winkler, 1886

Germanium sits between gallium and arsenic in Period 4.

It bridges metallic and non-metallic character in the p-block of the periodic table.

Atomic Mass Comparison
Gallium69.7 u
Germanium72.6 u
Arsenic74.9 u
Selenium79.0 u
Iron55.8 u

Germanium (72.6 u) is a metalloid, it sits at the chemical boundary between metals and non-metals, similar in position to silicon one period above it. Like silicon, germanium is a semiconductor that was once central to electronics.

What is germanium?

Germanium is a metalloid in Group 14 of the periodic table, sitting directly below silicon. It has 32 protons and four electrons in its outer shell. Like silicon, it is a semiconductor: its electrical conductivity lies between metals and insulators and can be controlled precisely by adding tiny amounts of impurities (doping). Crystalline germanium looks silver-grey and metallic but behaves chemically more like a non-metal. It is brittle and shatters rather than bending.

Germanium gets its name from Germania: the Latin name for Germany, chosen by its discoverer, the German chemist Clemens Winkler, as a patriotic tribute. Mendeleev had predicted the element in 1871 as eka-silicon, leaving a gap in the periodic table beneath silicon. When Winkler discovered it in 1886, the match with Mendeleev's predictions was so accurate, in atomic mass, density and chemical behaviour, that it was hailed as one of the greatest triumphs of periodic table theory.

Fact Mendeleev predicted the properties of germanium, which he called eka-silicon, in 1871, including its atomic mass (72, actual: 72.6), density (5.5, actual: 5.35 g/cm³) and the formula of its oxide (GeO₂). When Clemens Winkler found the real element 15 years later, the match was extraordinary: one of the most accurate predictions in the history of science.

Where you find germanium

On Earth

Germanium is rare, approx. 1.5 parts per million in the Earth's crust, and is never found as a free element. It is always dispersed in trace amounts in other minerals.

  • By-product of zinc smelting. Germanium occurs in sphalerite (zinc sulfide ore) and is the primary source of commercial germanium, recovered from the flue dust of zinc smelters.
  • Coal fly ash. Germanium concentrates in coal and is released during burning as fly ash, which can be processed to recover germanium.
  • Argyrodite. The rare mineral argyrodite (Ag₈GeS₆) was the ore from which Winkler first isolated germanium in 1886.

How we use germanium

  • Optical fibre cables. Germanium dioxide is added to the glass core of optical fibres to increase its refractive index, controlling how light travels through the fibre. Almost all the world's optical fibre internet cables use germanium-doped glass.
  • Infrared optics. Germanium is transparent to infrared light but opaque to visible light. Germanium lenses are used in thermal imaging cameras, night-vision equipment and infrared astronomy instruments.
  • Semiconductor electronics. Germanium transistors were the first working transistors (1947) and remained important until silicon took over in the 1960s. Germanium has made a comeback in high-speed SiGe (silicon-germanium) alloy transistors used in 4G and 5G chips.
  • Solar cells. Multi-junction solar cells for satellites use germanium as the bottom junction, capturing infrared photons that silicon cells would miss.
Did you know? The first ever working transistor, invented at Bell Labs in December 1947 by William Shockley, John Bardeen and Walter Brattain, was made from germanium. This tiny germanium point-contact transistor replaced the hot, fragile vacuum tube and launched the entire modern electronics industry. The inventors received the 1956 Nobel Prize in Physics. Germanium was used in transistors for approx. 15 years before silicon took over in the early 1960s.

How it was discovered

Clemens Winkler discovered germanium in 1886 while analysing the rare mineral argyrodite found in a silver mine in Germany's Erzgebirge mountains. After months of careful work, he isolated a new element and measured its properties. When he compared them to Mendeleev's 1871 prediction for eka-silicon, the match was startling. Winkler wrote to Mendeleev expressing his astonishment. The discovery became one of the most celebrated confirmations of the periodic table's power to predict the existence of unknown elements.

Deeper dive: germanium semiconductors and the transistor revolution

The transistor, invented using germanium in 1947, is the most manufactured object in human history. Modern computer chips contain billions of transistors, each a tiny switch that can be in an on or off state. The transistor replaced the vacuum tube, which was bulky, fragile, hot and power-hungry. A modern smartphone processor contains more transistors than there have been seconds since the Big Bang.

Germanium has a smaller band gap than silicon: the energy difference between its conduction and valence electron bands. This means electrons can jump between them more easily at lower voltages and lower temperatures. Germanium transistors work better at very low temperatures, which is why germanium-based transistors are still used in cryogenic (extremely cold) scientific equipment. In silicon-germanium (SiGe) alloy transistors, the germanium content tunes the band gap to achieve speeds impossible with pure silicon, enabling the high-frequency radio circuits in modern mobile phones.

Germanium is a metalloid that was predicted before it was discovered and has played a pivotal role in electronics history. Moving to 33 protons brings us to arsenic, a metalloid with a notorious history as a poison.