Molybdenum
Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele.
Identity
- Atomic mass
- 95.951 u
- Category
- Transition metals
- Group
- 6
- Period
- 5
- Block
- d
- Oxidation States
- +2, +3, +4, +5, +6
- Phase (25 °C)
- Solid
- Appearance
- gray metallic
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d5
- Short configuration
- [Kr] 4d5 5s1
- Electrons per shell
- 2, 8, 18, 13, 1
- Electronegativity (Pauling)
- 2.16
- Electron affinity
- 72.1 kJ/mol
- 1st ionization energy
- 684 kJ/mol
- Ionization energies
- 684 · 1560 · 2618 · 4480 · 5257… kJ/mol
Physical properties
- Melting point
- 2622.8 °C (2896 K)
- Boiling point
- 4638.9 °C (4912 K)
- Density
- 10.28 g/cm³
- Molar heat capacity
- 24.1 J/(mol·K)
Chemical behavior of molybdenum
Molybdenum is a group 6 transition metal with symbol Mo and atomic number 42. It is a hard silvery-gray metal with an exceptionally high melting point (2623 C) and good corrosion resistance. Its states range from +2 to +6, with +6 the most stable. It hardens steels, lubricates as sulfide and catalyzes fuel and chemical processes.
Reactivity
Mo + 3 Cl2 -> MoCl6
Molybdenum reacts with chlorine to form molybdenum hexachloride, a white solid that is the most stable compound.
Mo + 2 NH4VO3 -> MoS2 + ... (few reactions at room temperature)
Molybdenum is relatively inert at room temperature, but reacts with oxygen and acids at elevated temperatures.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Molybdenum disulfide | MoS2 | Solid lubricant; used in greases and industrial coatings |
| Molybdenum trioxide | MoO3 | White solid; precursor of molybdenum compounds and material for capacitors |
| Molybdenum(V) fluoride | MoF5 | White solid; used in electrolysis reagents and in purification stages |
Electron shell distribution
View in the atom builderIsotopes
Natural molybdenum has seven isotopes: molybdenum-98 (24.1 %), molybdenum-96 (16.7 %), molybdenum-95 (15.9 %), molybdenum-92 (14.8 %), molybdenum-94 (9.3 %), molybdenum-97 (9.6 %) and molybdenum-100 (9.6 %). Molybdenum-100 is slightly radioactive with an immense half-life. Molybdenum-98/100 feed technetium-99m generators via molybdenum-99.
Occurrence and production
Trace crustal element (1-2 ppm) as molybdenite (MoS2), wulfenite and powellite. Leading resources are in China, the United States, Chile and Peru. Much output comes as a by-product of copper refining, roasted from sulfide to oxide then reduced to metal.
History and origin of the name
Carl Wilhelm Scheele recognized in 1778 that molybdenite was a new element distinct from graphite and lead ores. Peter Jacob Hjelm isolated impure metal in 1781. The name comes from Greek molybdos (lead), for the resemblance of its ores to lead minerals.
Applications and relevance of molybdenum
Uses of the element
About 80 % goes to steels: high-strength low-alloy, stainless and tool steels for pipelines, structures, drills and dies. Pure metal serves furnace parts, heating elements, electrodes and thin films needing heat resistance.
Uses of its compounds
Disulfide lubricates where oils fail; oxides and molybdates catalyze hydrotreating of fuels; molybdates inhibit corrosion and supply the essential micronutrient; pigments color ceramics.
Health, safety and environment
Biological role
Molybdenum is an essential micronutrient: it centers enzymes such as xanthine oxidase, sulfite oxidase and aldehyde oxidase in humans, plus nitrogenase helpers in plants and microbes. Needs are tiny; deficiency is rare. Very high intakes disturb copper metabolism.
Safety
Metal is stable and low toxicity, but molybdenum trioxide dust and soluble molybdates irritate eyes and airways. Powder metallurgy needs ventilation and dust control. Soluble salts are harmful in large ingested doses.
Environment
Mining and roasting must control dust, sulfur gases and leachates. Molybdenum is persistent but generally low hazard at ambient levels; recycling alloy scrap recovers much of the metal.
Frequently asked questions about Molybdenum
Why does a little molybdenum make steel much stronger?
It forms fine carbides that pin grain boundaries and keep hardness during heat treatment. Small additions raise strength, hardenability and high-temperature performance without much carbon. Hence pipeline, structural and tool steels tuned by rolling and tempering.
Why is molybdenum used in chemical catalysts?
With cobalt or nickel it hydrotreats petroleum streams, stripping sulfur and impurities with hydrogen. It also drives oxidation and metathesis steps. Activity depends on composition, structure and conditions, so it is built into tailored catalyst supports.
What role does molybdenum play in living enzymes?
It sits at the active center of enzymes catalyzing nitrogen, sulfur and carbon steps. Humans use it in xanthine and sulfite oxidases; plants and microbes in nitrate and nitrogen chemistry. Function needs the metal built into a cofactor, not bare metal.
How does molybdenum help wear-resistant tools?
In tool steels and hard materials it joins carbides that keep hardness under hot working. This suits drills, dies and machining tools. Proportion is tuned: hot-work tools need different balance than precision cutters.
Why is molybdenum disulfide such a good lubricant?
Its crystal is sheets of Mo between sulfur layers that slide easily over each other, like graphite. It lubricates in vacuum, heat or load where oils break down. Used in greases, pastes and coatings for aerospace, automotive and heavy plant.
What makes molybdenum useful in furnaces?
Very high melting point plus useful hot strength suit furnace parts, heaters and supports. But hot molybdenum oxidizes fast in air, so duties need vacuum, protective gas or coatings. Temperature, atmosphere and load decide selection.
Why is molybdenum used in electrodes and electronics?
High melting point, useful conductivity and low vapor pressure at heat suit electrodes, contacts and thin-film stacks. Purity, deposition and compatibility with neighbors set device performance, since interfaces dominate.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.