Germanium (Ge)

Germanium has the ground-state electronic configuration \([Ar]3d^{10}\,4s^2\,4p^2\). It lies in Group 14 (carbon group) and Period 4, sharing properties with both metals and nonmetals—hence classified as a metalloid.

Germanium has a small band gap of about \(E_g = 0.66\,\text{eV}\) at 300 K. This allows limited electron excitation from the valence to the conduction band at room temperature, giving controllable conductivity. Doping with donor or acceptor atoms (e.g., As or Ga) creates n-type or p-type semiconductors used in diodes and transistors.

• Band gap: Ge (0.66 eV) < smaller than > Si (1.12 eV) → higher intrinsic conductivity but poorer high-temperature performance.
• Carrier mobility: Ge has higher electron/hole mobilities → faster devices.
• Usage: Early transistors used Ge; Si dominates modern ICs due to stability and oxide formation. Ge is still used in high-speed, infrared, and optoelectronic devices.

Germanium commonly shows +2 and +4 oxidation states. Examples include:

• +4: GeO₂, GeCl₄
• +2: GeO, GeCl₂ (less stable)

GeO₂ is an amphoteric oxide, dissolving in acids and bases to form germanate salts.

Germanium dioxide is amphoteric:

• With acid: \(\mathrm{GeO_2 + 4\,HCl \rightarrow GeCl_4 + 2\,H_2O}\)
• With base: \(\mathrm{GeO_2 + 2\,NaOH \rightarrow Na_2GeO_3 + H_2O}\)

This dual behavior reflects its intermediate character between metals and nonmetals.

GeO₂ increases refractive index and transparency in optical fibers, enabling low-loss light transmission. Crystalline Ge is transparent to infrared (IR) light from 2–14 μm, making it ideal for thermal imaging, IR spectrometers, and night-vision optics.

Germanium occurs in trace amounts in sphalerite (ZnS) and coal ash. It is recovered as a by-product of zinc smelting or coal combustion through oxidation, solvent extraction, and reduction of GeO₂ with hydrogen:

\(\mathrm{GeO_2 + 2\,H_2 \rightarrow Ge + 2\,H_2O}\)

Natural germanium consists of stable isotopes: ⁷⁰Ge, ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge. The last isotope, ⁷⁶Ge, is double-beta active (undergoing very slow decay), making it important in neutrino physics experiments such as GERDA and LEGEND.

Upon hydrolysis, germanium tetrachloride forms germanium dioxide and hydrochloric acid:

\(\mathrm{GeCl_4 + 2\,H_2O \rightarrow GeO_2 + 4\,HCl}\)

This reaction is used in the preparation of GeO₂ for glass and fiber applications.

Elemental Ge is low-toxicity, but some compounds (e.g., GeCl₄, organogermanes) are corrosive or irritant. Proper ventilation, gloves, and protective eyewear are recommended. Chronic overexposure to soluble germanium salts can affect kidneys and nervous system.