Molybdenum (Mo)

Stable isotopes of molybdenum available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Mo-92  42  50  91.906810 14.77%  75.00-98.70%  Metal
Mo-92 42 50 91.906810 14.77% 75.00-98.70% Oxide
Mo-94 42 52 93.905087 9.23% >98.00% Metal
Mo-94 42 52 93.905087 9.23% >98.00% Oxide
Mo-95 42 53 94.905841 15.90% ≥94.30% Metal
Mo-95 42 53 94.905841 15.90% ≥94.30% Oxide
Mo-96 42 54 95.904678 16.68% >95.00% Metal
Mo-96 42 54 95.904678 16.68% >95.00% Oxide
Mo-97 42 55 96.906020 9.56% ≥96.60% Metal
Mo-97 42 55 96.906020 9.56% ≥96.60% Oxide
Mo-98 42 56 97.905407 24.19% >98.40% Metal
Mo-98 42 56 97.905407 24.19% >98.40% Oxide
Mo-100  42  58  99.907477 9.67%  90.00-99.86% Metal
Mo-100 42 58 99.907477 9.67% 90.00-99.86% Oxide

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Molybdenum was discovered in 1781 by Carl William Scheele. Its name originates with the Greek word molybdos, meaning “lead.” It does not occur free in nature, and it is a necessary trace element in plant nutrition.

Molybdenum is a silvery-white metal or grayish-black powder with a cubic crystalline structure. It has high strength at very high temperatures and oxidizes rapidly above 1000 °F in air at sea level, but it is stable in an upper atmosphere. It is insoluble in hydrochloric or hydrofluoric acids, ammonia, sodium hydroxide, water or dilute sulfuric acid, and soluble in hot concentrated sulfuric or nitric acids. At ordinary temperatures, molybdenum metal is fairly stable to air, water and most mineral acids. The metal shows high resistance to HCl, H2SO4, HF and H3PO4, and most other mineral acids in the absence of any oxidizing agent. However, the metal is attacked by nitric acid and aqua regia.

Molybdenum is very stable to oxygen at ambient temperatures; however, when heated in air or oxygen to red heat, the metal readily converts to trioxide. When bromine vapor is passed over molybdenum metal at 600-700 ºC in an atmosphere of nitrogen, the product is trimeric molybdenum dibromide. The metal has very little affinity for hydrogen, even in a finely divided state. When heated with carbon monoxide at temperatures above 1000 ºC, no carbonyl is obtained, but a thin film of molybdenum carbide forms over the metal. The metal is used as the starting material to prepare many of its salts.

The largest quantities of molybdenum produced are consumed in the steel industry. The metal is incorporated to impart high resistance and hardness to the steel, as well as to improve its mechanical properties. In the chemical industry, molybdenum compounds are used widely in coloring agents and solid lubricants. Molybdenum compounds are also used as catalysts in many oxidation-reduction reactions and in petroleum refining for production of high-octane gasoline. 

Properties of Molybdenum

Name Molybdenum 
Symbol Mo 
Atomic number 42 
Atomic weight 95.94 
Standard state Solid at 298° °K 
CAS Registry ID 7439-98-7 
Group in periodic table
Group name None 
Period in periodic table
Block in periodic table d-block 
Color Grey metallic 
Classification Metallic 
Melting point 2623 °C
Boiling point 4612 °C
Vaporization point 4639 °C
Thermal conductivity 138 W/(m·K) at 298.2 °K
Electrical resistivity 5.0 µΩ·cm at 0 °C 
Electronegativity 1.9 
Specific heat 0.25 kJ/kg K 
Heat of vaporization 600 kJ·mol-1 at 4612 °C
Heat of fusion 36 kJ·mol-1
Density of liquid 9.33 g/cm3 at 2623 °C
Density of solid 10.28 g/cm
Electron configuration [Kr]4d55s1
Atomic radius 1.36 Å (coordination number 8) 
Ionic radius Mo3+: 0.92 Å and Mo6+: 0.62 Å 
Oxidation states 0, +2, +3, +4, +5, +6
Most stable oxidation state +6
Atomic volume 9.41 cm3/mol

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