By John Brennan
Updated Mar 24, 2022
Tungsten (atomic number 74) is a dense, gray metal renowned for its exceptionally high melting point and excellent mechanical properties. While its most familiar role is in incandescent bulb filaments, its industrial importance largely stems from the production of tungsten carbide and its use in high‑temperature alloys. At the heart of these applications lies the nature of the bonds that hold tungsten atoms together.
In its isolated ground state, a tungsten atom has the electronic configuration [Xe] 4f14 5d4 6s2. However, when atoms pack into a crystal lattice, the energy levels shift: the 5d sub‑shell becomes fully occupied (five electrons) while the 6s sub‑shell holds a single electron. The 5d electrons are capable of forming directional, covalent‑type interactions that are relatively localized between neighboring atoms, whereas the 6s electrons delocalize across the lattice.
In the solid state, the delocalized 6s electrons behave like a “sea” of mobile charge that permeates the metal. This electron gas binds the positively charged tungsten nuclei together, giving the material its characteristic metallic bonding. The overlap of many atomic orbitals creates a dense band of energy levels that electrons can occupy, which explains tungsten’s high electrical conductivity and its resistance to deformation.
Tungsten crystallizes in several allotropes: the most common is the body‑centered cubic alpha phase, which is the most thermodynamically stable. A high‑temperature beta phase also exists; upon cooling, the beta structure transforms into alpha. The metallic bonding, combined with a close packing of atoms, results in a metal that is both malleable and ductile—typical traits of metals where atoms are not locked into a rigid lattice like diamond.
When tungsten reacts with nonmetallic elements or ligands, it forms coordination complexes and covalent compounds. The shared‑electron nature of these bonds contrasts with the metallic bonding in the elemental metal. Tungsten’s oxidation states in such compounds range from –2 to +6, reflecting the diversity of its chemistry. At elevated temperatures, tungsten readily oxidizes; this is why incandescent bulbs are filled with inert gases—to prevent filament degradation.
