Cadmium: the essentials
Cadmium is a soft, bluish-white metal and is easily cut with a knife. It is similar in many respects to zinc. Interestingly, aa characteristic cadmium "scream" is heard on bending a cadmium bar (such as that illustrated above). Cadmium and its compounds are highly toxic. Silver solder, which contains cadmium, should be handled with care.
Cartoon by Nick D Kim ([Science and Ink], used by permission).
Cadmium: historical information
Cadmium was discovered by Friedrich Stromeyer in 1817 from an impurity in some samples pf zinc carbonate, ZnCO3. He noted that these particular samples changed colour on heating, which pure zinc carbonate does not. He was persistent enough to follow this observation through and he eventually isolated some cadmium metal by roasting and reduction of the sulphide.
Cadmium around us Read more »
Cadmium might be a necessary element in very, very, small quantities in rats.
Inhalation of cadmium dust causes problems for the respiratory tract and for the kidneys. Death may follow. Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys.
Cadmium ores are rare. Cadmium occurs associated with zinc ores such as sphalerite (zinc sulphide, ZnS). Greenockite (CdS) is the only mineral of any consequence which contains cadmium. Most cadmium is produced as a by-product from the extraction of zinc, copper, and lead ores.
|Location||ppb by weight||ppb by atoms||Links|
|Human||700 ppb by weight||39 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 594.22 [321.07 °C (609.93 °F)] K
- Boiling point: 1040 [767 °C (1413 °F)] K
- Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of cadmium is: hcp (hexagonal close-packed).
Cadmium: orbital properties Read more »
Cadmium atoms have 48 electrons and the shell structure is 22.214.171.124.2. The ground state electronic configuration of neutral Cadmium is [Kr].4d10.5s2 and the term symbol of Cadmium is 1S0.
- Pauling electronegativity: 1.69 (Pauling units)
- First ionisation energy: 867.8 kJ mol‑1
- Second ionisation energy: 1631.4 kJ mol‑1
Isolation: it is rare that preparation of cadmium in the laboratory should be required bacause of environmental concerns about cadmium. The isolation of cadmium is associated with zinc recovery as cadmium is an impurity in zinc ores. Most zinc production is based upon sulphide ores. These are roasted in industrial plants to form zinc oxide, ZnO. This may be reduced with carbon to form zinc metal, but in practice ingenious technology is required to ensure that the resulting zinc does not contain oxide impurities.
ZnO + C → Zn + CO
ZnO + CO → Zn + CO2
CO2 + C → 2CO
After this process, zinc may be refined by distillation under vacuum and this process also allows the separation of any cadmium present in the crude zinc.
The other type of extraction of zinc is electrolytic. Dissolution of crude zinc oxide, ZnO, in sulphuric acid gives zinc sulphate, ZnSO4 in solution. Before electrolysis to produce zinc, the cadmium impurity and is removed as a precipitate by the addition of zinc dust as cadmium sulphate.
Cadmium isotopes Read more »
The nine stable Cadmium isotopes are used for many different purposes. Cd-110 is used for the production of the radioisotope In-110, while Cd-112 is used in the production of the widely used diagnostic radioisotope In-111. Cd-108 is used in the production of Cd-109 which is a calibration source for 88 keV gamma radiation. The even numbered Cd isotopes (mainly Cd-110, Cd-112, Cd-114 and Cd-116) are used to improve the power output and coherence length of HeCd lasers.
|106Cd||105.906461 (7)||1.25 (6)||0|
|108Cd||107.904176 (6)||0.89 (3)||0|
|110Cd||109.903005 (4)||12.49 (18)||0|
|111Cd||110.904182 (3)||12.80 (12)||1/2||-0.5948857|
|112Cd||111.902757 (3)||24.13 (21)||0|
|113Cd||112.904400 (3)||12.22 (12)||1/2||-0.6223005|
|114Cd||113.903357 (3)||28.73 (42)||0|
|116Cd||115.904755 (4)||7.49 (18)||0|