Germanium at a glance
- Atomic number
- 32
- Symbol
- Ge
- Atomic mass
- 72.63 u
- Category
- Metalloid
- Group / period
- 14 / 4
- Electron configuration
- [Ar] 3d 10 4s 2 4p 2
- State at 25 °C
- Solid
- Melting point
- 938.3 °C
- Boiling point
- 2833 °C
- Density
- 5.323 g/cm³
- Electronegativity
- 2.01
- 1st ionization energy
- 762 kJ/mol
- Oxidation states
- +4, +2
- Discovered
- 1886
Atomic structure
A neutral germanium atom has 32 protons and 32 electrons, and its most common isotope carries about 42 neutrons. One atom weighs about 1.21 × 10⁻²⁵ kg, so a mole of germanium (6.022 × 10²³ atoms) weighs 72.63 g. That nucleus holds 1.31 neutrons for every proton. The electrons fill 4 shells (K 2, L 8, M 18, N 4), which gives the configuration [Ar] 3d 10 4s 2 4p 2. With 4 electrons in its outer shell, it usually shares electrons in covalent bonds. It has 5 stable isotopes: Ge-70, Ge-72, Ge-73, Ge-74 and Ge-76. Its most common isotope, Ge-74, has the same mass number as Se-74: isobars, nuclei of different elements with 74 nucleons each.
Physical properties
At room temperature (25 °C) germanium is a solid. It melts at 938.3 °C and boils at 2833 °C, so it stays liquid across a 1895-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 5.323 g/cm³, 5.32 times as dense as water. Its atoms have a radius of about 125 pm (Gallium next door is 130 pm). In the solid, its atoms pack into a diamond cubic lattice.
Chemical behaviour
Its electronegativity is 2.01 on the Pauling scale. Pulling off its outermost electron takes 762 kJ/mol, less than Silicon above it (787 kJ/mol). A bond between germanium and chlorine would be polar covalent, with an electronegativity difference of 1.2. It releases 119 kJ/mol when it gains an extra electron. Its common oxidation states are +4, +2, so in compounds you will usually meet it as Ge⁴⁺ and Ge²⁺. Group 14 also holds Carbon, Silicon, Tin, Lead and Flerovium, which share its outer-shell pattern. Its Lewis symbol is Ge surrounded by 4 dots.
Where it comes from
It makes up 1.5 mg/kg of Earth's crust, the 55th most abundant element there. It was first identified in 1886, making it the 74th element to be discovered (counting the 11 known since antiquity together).