Manganese

Manganese,  ₂₅Mn

General properties
Name, symbol	Manganese, Mn
Appearance	Silvery-gray solid
Manganese in the periodic table
- ↑ Mn ↓ Tc Chromium ← Manganese → Iron
Atomic number	25
Standard atomic weight (Ar)	54.938044(3)
Group, block	, d-block
Period	period 4
Electron configuration	[Ar] 3d5 4s2
per shell	2, 8, 13, 2
Physical properties
Silvery-gray
Phase	Solid
Melting point	1519 K ​(1246 °C, ​2275 °F)
Boiling point	2334 K ​(2061 °C, ​​3742 °F)
Density near r.t.	7.21 g/cm3
when liquid, at	5.95 g/cm3
Heat of fusion	12.91 kJ/mol
Heat of	221 kJ/mol
Molar heat capacity	26.32 J/(mol·K)
pressure
Atomic properties
Oxidation states	7, 6, 5, 4, 3, 2, 1, −1, −2, −3 ​acidic, basic or amphoteric; depending on the oxidation state
Electronegativity	Pauling scale: 1.55
energies	1st: 717.3 kJ/mol 2nd: 1509.0 kJ/mol 3rd: 3248 kJ/mol (more)
Atomic radius	empirical: 127 pm
Covalent radius	Low spin: 139±5 pm High spin: 161±8 pm
Miscellanea
Crystal structure	​​body-centered cubic (bcc)
Speed of sound thin rod	5150 m/s (at 20 °C)
Thermal expansion	21.7 µm/(m·K) (at 25 °C)
Thermal conductivity	7.81 W/(m·K)
Electrical resistivity	1.44 Ω·m (at 20 °C)
Magnetic ordering	Paramagnetic
Young's modulus	198 GPa
Bulk modulus	120 GPa
Mohs hardness	6
Brinell hardness	196 MPa
CAS Registry Number	7439-96-5
History
Discovery	Torbern Olof Bergman (1770)
First isolation	Johann Gottlieb Gahn (1774)

Manganese is a chemical element with symbol Mn and atomic number 25. It is a transition metal, often used in various steels and more often in chemistry, due to its large number of oxidation states.

Properties

Chemical

Manganese slowly tarnishes in the air or in water containing dissolved oxygen.

Manganese reacts with all halogens and most strong acids.

Manganese has 10 oxidation states, though the most common ones are +2, +3, +4, +6, and +7. Manganese compounds in oxidation state +7 are strong oxidizers.

Physical

Manganese is a silvery-gray metal, which has similar properties to iron. It is hard and very brittle. It melts at 1246 °C and boils at 2061 °C. It has a density of 7.21 g/cm³, being slightly less dense than iron.

Availability

Manganese metal is sold by various chemical suppliers. Manganese samples can also be bought from eBay and Amazon.

Isolation

Manganese metal can be extracted from manganese dioxide, readily found in many zinc-carbon batteries. The oxide can be reduced in a thermite reaction with aluminium or even magnesium, although carbon can also be used.

3 MnO₂ + 4 Al → 3 Mn + 2 Al₂O₃

MnO₂ + C → Mn + CO₂

The reaction with aluminium is exothermic enough to reach the boiling point of manganese. Manganese lumps are somewhat difficult to separate from the resulting slag. A fluxing agent such as calcium fluoride should be added, which also acts as a heat sink.

Better results can be obtained by replacing manganese dioxide with manganese(II,III) oxide (Mn₃O₄).

Manganese can also be extracted from manganese steels (mangalloy) by dissolving it in an acid, separating the manganese salt, and reducing it to manganese metal through various methods.

Projects

• Make manganese dioxide
• Make potassium permanganate
• Element collecting

Handling

Safety

Manganese is an essential trace element for all known living organisms, however, in large quantities has neurotoxic effects. It can cause a poisoning syndrome in mammals, especially when inhaled, leading to severe if not irreversible neurological damage.

Storage

Bulk manganese metal can be stored in any container, away from any corrosive vapors. Powdered manganese should be kept in sealed containers.

Disposal

Manganese compounds should be converted to insoluble or less harmful compounds, such as manganese(II,III) oxide. These can be placed in the same container as Zn-MnO₂ batteries, as companies that deal in battery disposal will work with manganese wastes from damaged or leaking batteries.

References

Relevant Sciencemadness threads

• Manganese Thermite with Lime
• Removal of Iron from Manganese