Magnesium

Additional physico-chemical information

Description of key information

Expert Judgement 
Due to the absence of chemical groups or other structural alerts this substance is not considered to exhibit an high hazard potential.
Magnesium in Magnesium Alloys  is from The alkaline earth metals: Its functional groups indicate low priority for further work based on a low hazard potential.
Therefore testing for Additional physico-chemical properties does not need to be performed. 

Additional information

Expert Judgement

Due to the absence of chemical groups or other structural alerts this substance is not considered to exhibit an high hazard potential.

Magnesium in Magnesium Alloys is from The alkaline earth metals: Its functional groups indicatelow priority for further work based on a low hazard potential.

 

Therefore testing for Additional physico-chemical properties does not need to be performed.

 

Some Additional physico-chemical information is available:

 

Atomic properties 
The unalloyed magnesium has the following atomic characteristics: 
1. Symbol: Mg. 
2. Atomic number: 12. 
3. Electron configuration in free atoms: (2) (8) 2. 
4. Orbital electron states in free atoms: 1s², 2s², 2p⁶, 3s². 
5. Atomic isotopes 78.99% Mg²⁴ (mass = 23.98504), 10.00% Mg²⁵ (mass = 24.98584) and 11.07% Mg²⁶ (mass = 25.98259). 
6. Atomic weight: 24.3050(6). 
7. Atomic volume: 14.0 cm³/moll. 

Crystal Structure 
The crystal structure of pure magnesium under atmospheric pressure is hexagonal close-packed. The lattice parameters of pure magnesium at 25 ^oC (77 ^oF) were in agreement within ±0.01% of the assessed values of a (side length) = 0.32092 nm and c (height) = 0.52105 nm. The actual c/a ratio at room temperature is 1.6236 making magnesium nearly perfectly closed packed

 

 

. Mass Characteristics 
The density of magnesium at 20 ^oC (68 ^oF) is 1.738 g/cm³ (0.0628 lb/in.³). At the melting temperature (650 ^oC, or 1202 ^oF), the density in solid state is approximately 1.65 g/cm³ (0.0596 lb/in.³); in liquid state, it is approximately 1.58 g/cm³ (0.0571 lb/in.³). 

Volume change on freezing. Volumetric shrinkage of 4.2% occurs on freezing (1.5% linear shrinkage). 

Volume change on cooling. Volumetric shrinkage of 5% occurs on cooling solid form from 650 ^oC to 20 ^oC (1202 ^oF to 68 ^oF) (1.7% linear shrinkage). 

Thermal properties 
The melting point of pure magnesium under atmospheric pressure is 650 ^oC ± 1 ^oC (1202 ^oF ± 1.8 ^oF). 

The boiling point of pure magnesium under atmospheric pressure is 1090 ^oC (1994 ^oF). 

Thermal expansion. The coefficients of linear thermal expansion for polycrystalline magnesium at low temperatures can be expressed as: 

α_t = (25.0 + 0.0188t ^oC) μm/m x ^oC 
or 
α_t = (13.7 + 0.0058t ^oF) μ in/in. x ^oF 

Thermodynamic properties 
Specific heat capacities at constant pressure (C_p) in units of J/mol x K are: 

1. Solid (298-923 K): 26.19 - 1.01 x 10^-3 T - 1.60 x 10⁵/T² + 8.41 x 10^-6 T² 
2. Liquid (923-1600 K): 212.74 - 205.66 x 10^-3T - 350.15 x 10⁵/T² + 61.56 x 10⁶ 
3. Monatomic gas (298-2000 K): 20.79 
4. Monatomic gas (2000-3000 K): 22.12 - 1.24 x 10^-3T 
5. Diatomic gas (298-900 K): 20.45 + 0.48 x 10^-3T + 3.23 x 10⁵/T² - 0.19 x 10⁶T 
6. Diatomic gas (900-3000 K): 20.78 + 2.71 x 10⁵/T² 

 

 

Electrical properties 
Electrical conductivity is 38.6% IACS. 
Electrical resistivity (ρ) for single crystals of magnesium at 20 ^oC (68 ^oF) is 45.3 nΩ · m along the a-axis and 37.8 nΩ · m along the c-axis. The temperature coefficient at 20 ^oC (68 ^oF) is 0.143 nΩ · m/K along the c-axis. 
The contact potential is +44mV versus saturated calomel electrode at 25 ^oC (77 ^oF) and -0.222 mV versus copper at 27 ^oC (81 ^oF). 
The electrochemical equivalent is 126 mg/C. 
The standard electrode potential is -2.40 V versus hydrogen. 
The ionization potential is 7.65 eV for Mg⁺ and 15.05 eV for Mg²⁺. 
The electrolytic solution potential is 1.63 mV versus saturated calomel electrode at 25 ^oC (77 ^oF) in aerated NaCl solution. 
The Work Function. Two values have been published: 3.61 eV and 3.66 eV. 

Magnetic properties 
Magnetic susceptibility is 0.00627 to 0.00632 mks (mass) 
Magnetic permeability is 1.000012. 
The Hall constant is -1.06 x 10 ^-16 Ω · m/(A/m) 

Optical properties 
Reflectivity is 0.72 at λ = 0.500 μm, 0.74 at λ = 1.00 μm, 0.80 at λ = 3.0 μm, 0.93 at λ = 9.0 μm. 
Solar absorptivity is 0.31. 
Emissivity is 0.07 at 22 ^oC (72 ^oF). 
The absorption constant is 4.42 at λ = 0.589 μm. 
The refractive index is 0.37 at λ = 0.589 μm. 

Nuclear properties 
Neutron absorption cross-section values in barns per atom (1 barn = 10^-24 cm²) for thermal neutron radiation are: 
0.063 ± 0.004 for natural magnesium 
0.03 ± for Mg²⁴ 
0.27 ± for Mg²⁵ 
0.03 ± for Mg²⁶ 
Magnesium has the following radioactive isotopes: Mg²¹, Mg²², Mg²³, Mg²⁷, and Mg²⁸. 
The x-ray absorption coefficient μm is 32.9 m²/kg. 

 

 

Chemical Properties

(i) Action of oxygen or air

Magnesium does not react with dry air but slowly gets tarnished in most air due to the formation of a thin film of the oxide, MgO. It burns in oxygen or air with a dazzling light.

                    Δ

2Mg + O₂ ——→ 2MgO                 

 

(ii)    Action of CO₂ and SO₂

Because of its great affinity for oxygen magnesium keeps on burning even in CO₂ or SO₂.

                       Δ

2Mg + CO₂ ——→ 2MgO + C               

                Δ

2Mg + SO₂ ——→ 2MgO + S

 

(iii) Action of nitrogen

On heating magnesium combines with nitrogen to form magnesium nitride.

3Mg + N₂ ——→ Mg₃N₂               

Thus when magnesium burns in air both the oxide and the nitride are formed.

(iv)   Action of halogens

Magnesium on heating with halogens readily forms the halides e.g.

                   Δ

Mg + CI₂ ——→ MgCI₂               

 

(v)    Action of water

Magnesium does not decompose water in cold but decomposes boiling water or steam.

Mg + H₂O ( steam) ——→ MgO + H₂             

(vi)   Action of Acids

Dilute acids reacts with magnesium to produce dihydrogen.

 Mg + 2HCI ——→ MgCi₂ + H₂              

  Mg + H₂SO₄ ——→ MgSO₄ + H₂             

      (dil)              

Mg + 2HNO₃ ——→ Mg ( NO₃)₂ + H₂

However with conc. H₂SO₄, SO₂ is produced

Mg + 2H₂SO₄ ——→ MgSo₄  + SO₂ + 2H₂O             

     (conc.)

 

(vii) Reaction with alkyl halide

Magnesium reacts with alkyl halides in dry ether to form covalent compound called Grignard reagent.

               Dry ether

Mg + C₂H₅I ——→C₂H₅MgI