Cadmium

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Cadmium,  48Cd
General properties
Name, symbol Cadmium, Cd
Appearance Silvery-gray
Cadmium in the periodic table
Zn

Cd

Hg
SilverCadmiumIndium
Atomic number 48
Standard atomic weight (Ar) 112.414(4)
Group, block , d-block
Period period 5
Electron configuration [Kr] 4d10 5s2
per shell
2, 8, 18, 18, 2
Physical properties
Silvery-grey
Phase Solid
Melting point 594.22 K ​(321.07 °C, ​609.93 °F)
Boiling point 1040 K ​(767 °C, ​1413 °F)
Density near r.t. 8.65 g/cm3
when liquid, at  7.996 g/cm3
Heat of fusion 6.21 kJ/mol
Heat of 99.87 kJ/mol
Molar heat capacity 26.020 J/(mol·K)
 pressure
Atomic properties
Oxidation states 2, 1, −2 ​(a mildly basic oxide)
Electronegativity Pauling scale: 1.69
energies 1st: 867.8 kJ/mol
2nd: 1631.4 kJ/mol
3rd: 3616 kJ/mol
Atomic radius empirical: 151 pm
Covalent radius 144±9 pm
Van der Waals radius 158 pm
Miscellanea
Crystal structure
Speed of sound thin rod 2310 m/s (at 20 °C)
Thermal expansion 30.8 µm/(m·K) (at 25 °C)
Thermal conductivity 96.6 W/(m·K)
Electrical resistivity 72.7 Ω·m at 22 °C
Magnetic ordering Diamagnetic
Young's modulus 50 GPa
Shear modulus 19 GPa
Bulk modulus 42 GPa
Poisson ratio 0.30
Mohs hardness 2.0
Brinell hardness 203–220 MPa
CAS Registry Number 7440-43-9
History
Discovery Karl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)
Named by Friedrich Stromeyer (1817)
· references

Cadmium is a chemical element with symbol Cd and atomic number 48. It is a toxic metal with a few applications as pure metal. Although it's classified as a transition metal, cadmium's properties are closer to that of post-transition metals and some sources consider group 12 to be post-transition metals.

Properties

Chemical

Cadmium resists corrosion in open air by forming a protective oxide layer on it's surface, a property similar to that of the metal above, zinc.

Cadmium burns in air to form brown amorphous cadmium oxide (CdO). The crystalline form of CdO is a dark red solid which changes color when heated, similar to zinc oxide. Cadmium oxide is a slightly basic oxide.

Cadmium metal dissolves in hydrochloric acid, nitric acid and sulfuric acid to yield their respective salts.

Similar to mercury, cadmium also displays the +1 oxidation state, which can be obtained by dissolving cadmium metal in a mixture of cadmium chloride and aluminium chloride, forming the Cd22+ cation, which is similar to the Hg22+ cation in mercury(I) chloride.

Physical

Cadmium is a soft, malleable, ductile silvery-gray or grayish-white metal. Like the metal above it, zinc, cadmium has a low melting point, of only 321 °C and a boiling point of 767 °C, much lower than that of lead (1749 °C), another metal with a similar melting point (327 °C). It has a density of 7.996 g/cm3.

Availability

Cadmium metal can be found in the anode of Ni-Cd batteries, where it's usually plated as a sponge on a metal frame. It can be extracted by dissolving it with an acid and reducing the salt to metal.

Certain platings on aircraft parts contain cadmium metal.

An interesting source of cadmium are certain Made in China jewelries, such as pendants, necklaces, bracelets, often sold at a very cheap price, and produced by various "shady" Chinese companies. While most Chinese secondhand stores are very likely to have such products, cadmium jewelry is also sold by various big companies, even in malls. Some jewelries can have as much as 99.6 % cadmium by weight.[1]

Cadmium compounds such as cadmium sulfide (Cadmium yellow), cadmium selenide (Cadmium red), used as pigments, can also be used to make cadmium metal.

In the European Union, the Restriction of Hazardous Substances Directive limits the use of cadmium in products and restricts its use in the manufacture of various types of electronic and electrical equipment.

Isolation

Cadmium metal can be obtained by reducing cadmium sulfide.

Projects

  • Make cadmium selenide
  • Make Ni-Cd battery
  • Make CdS quantum dots

Handling

Safety

Cadmium and its salts are extremely toxic to organisms. Organocadmium compounds are deadly in minute doses. Cadmium is classified as a potent carcinogen. Certain insoluble compounds such as cadmium sulfide however, have lower toxicity.

Storage

Cadmium should be stored in closed containers or ampouled.

Disposal

Cadmium must be taken to speacial disposal centers and NEVER RELEASED IN THE ENVIRONMENT.

References

  1. https://www.youtube.com/watch?v=208-irQ1Yus

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