Molybdenum
 | |||||
| General properties | |||||
|---|---|---|---|---|---|
| Name, symbol | Molybdenum, Mo | ||||
| Appearance | Silvery-gray metal | ||||
| Molybdenum in the periodic table | |||||
| |||||
| Atomic number | 42 | ||||
| Standard atomic weight (Ar) | 95.95(1) | ||||
| Group, block | VI; d-block | ||||
| Period | period 5 | ||||
| Electron configuration | [Kr] 4d5 5s1 | ||||
per shell | 2, 8, 18, 13, 1 | ||||
| Physical properties | |||||
| Silvery-gray | |||||
| Phase | Solid | ||||
| Melting point | 2896 K (2623 °C, 4753 °F) | ||||
| Boiling point | 4912 K (4639 °C, 8382 °F) | ||||
| Density near r.t. | 10.28 g/cm3 | ||||
| when liquid, at | 9.33 g/cm3 | ||||
| Heat of fusion | 37.48 kJ/mol | ||||
| Heat of | 598 kJ/mol | ||||
| Molar heat capacity | 24.06 J/(mol·K) | ||||
| pressure | |||||
| Atomic properties | |||||
| Oxidation states | 6, 5, 4, 3, 2, 1, −1, −2, −4 (a strongly acidic oxide) | ||||
| Electronegativity | Pauling scale: 2.16 | ||||
| energies |
1st: 684.3 kJ/mol 2nd: 1560 kJ/mol 3rd: 2618 kJ/mol | ||||
| Atomic radius | empirical: 139 pm | ||||
| Covalent radius | 154±5 pm | ||||
| Miscellanea | |||||
| Crystal structure | body-centered cubic (bcc) | ||||
| Speed of sound thin rod | 5400 m/s (at ) | ||||
| Thermal expansion | 4.8 µm/(m·K) (at 25 °C) | ||||
| Thermal conductivity | 138 W/(m·K) | ||||
| Thermal diffusivity | 54.3 mm2/s (at 300 K) (at 300 K) | ||||
| Electrical resistivity | 53.4 Ω·m (at 20 °C) | ||||
| Magnetic ordering | Paramagnetic | ||||
| Young's modulus | 329 GPa | ||||
| Shear modulus | 126 GPa | ||||
| Bulk modulus | 230 GPa | ||||
| Poisson ratio | 0.31 | ||||
| Mohs hardness | 5.5 | ||||
| Vickers hardness | 1400–2740 MPa | ||||
| Brinell hardness | 1370–2500 MPa | ||||
| CAS Registry Number | 7439-98-7 | ||||
| History | |||||
| Discovery | Carl Wilhelm Scheele (1778) | ||||
| First isolation | Peter Jacob Hjelm (1781) | ||||
Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, which in turn is from Ancient Greek molybdos (Μόλυβδος), meaning "lead", since its ores were confused with lead ores.
Contents
Properties
Chemical
Molybdenum is resistant to most forms of corrosion. Weak oxidation of molybdenum begins at 300 °C, with bulk oxidation occurring at over 600 °C. Molybdenum trioxide is the main oxide that forms:
- 2 Mo + 3 O2 → 2 MoO3
Physical
Molybdenum is a very hard silvery-grey metal, with a Mohs hardness of 5.5. It has a high melting point, of 2,623 °C and a boiling point of 4639 °C. It is quite dense, with a density of 10.28 g/cm3. It has the second lowest coefficients of thermal expansion after pure tungsten among the metals.
Availability
Molybdenum is sold by various chemical suppliers and metal companies.
It is also found in many high-strength steels, which are used for various tools, although the percentage is small, between 0.2–5%, although most common steel alloys have <1% molybdenum.
The support wiring that holds the tungsten filament in light bulbs is made of molybdenum. Likewise, the bridge that connects the tungsten filament to the electric wiring in certain light bulbs, like the car ones is made of molybdenum. However, one would need a huge amount of light bulbs to obtain a useful amount of molybdenum.
Isolation
Molybdenum metal can be made by reducing molybdenum trioxide with hydrogen at high temperatures.
- MoO3 + 3 H2 → Mo + 3 H2O
Projects
- Make molybdenum trioxide
- Make sodium molybdate
- Grow crystals (molybdenum crucibles)
Handling
Safety
Molybdenum has low reactivity and thus is not toxic for the organism. Direct contact with molybdenum does not cause dermatitis. Molybdenum is an essential trace element and crucial for the survival of animals.
The most important role of molybdenum in living organisms is as a metal heteroatom at the active site in various enzymes, most notably in nitrogen fixation, process encountered in certain bacteria.
However, molybdenum fumes and compounds are known to display toxicity and should be candled with care. Molybdenum halides hydrolyze in contact with moist air, releasing corrosive fumes of hydrochloric acid.
Storage
Molybdenum does not require special storage and can be stored in any container.
Disposal
Molybdenum and its compounds display little toxicity and can be dumped in trash or recycled.
