Cadmium
|
|
| General |
| Name, Symbol, Number | Cadmium, Cd, 48 |
| Chemical series | Transition metals |
| Group, Period, Block | 12, 5 , d |
| Density, Hardness | 8650 kg/m3, 2 |
| Appearance | Silvery gray metallic
|
| Atomic Properties |
| Atomic weight | 112.411 amu |
| Atomic radius (calc.) | 155 (161) pm |
| Covalent radius | 148 pm |
| van der Waals radius | 158 pm |
| Electron configuration | [Kr]4d4d10 5s2 |
| e- 's per energy level | 2, 8, 18, 18, 2 |
| Oxidation states (Oxide) | 2 (mildly basic) |
| Crystal structure | Hexagonal |
| Physical Properties |
| State of matter | Solid (__) |
| Melting point | 594.22 K (609.93 °F) |
| Boiling point | 1040 K (1413 °F) |
| Molar volume | 13.00 ×1010-3 m3/mol |
| Heat of vaporization | 100 kJ/mol |
| Heat of fusion | 6.192 kJ/mol |
| Vapor pressure | 14.8 Pa at 597 K |
| Speed of sound | 2310 m/s at 293.15 K |
| Miscellaneous |
| Electronegativity | 1.69 (Pauling scale) |
| Specific heat capacity | 233 J/(kg*K) |
| Electrical conductivity | 13.8 106/m ohm |
| Thermal conductivity | 96.8 W/(m*K) |
| 1st ionization potential | 867.8 kJ/mol |
| 2nd ionization potential | 1631.4 kJ/mol |
| 3rd ionization potential | 3616 kJ/mol |
| Most Stable Isotopes |
| iso | NA | half-life | DM | DE MeV | DP |
| 188Cd | 0.89% | Cd is stable with 60 neutrons |
| 109Cd | {syn.} | 462.6 d | &epsilon | 0.214 | 109Ag |
| 110Cd | 12.49% | Cd is stable with 62 neutrons |
| 111Cd | 12.8% | Cd is stable with 63 neutrons |
| 112Cd | 24.13% | Cd is stable with 64 neutrons |
| 113Cd | {syn.} | 7.7 E15 y | β- | 0.316 | 113In |
| 113Cdm | {syn.} | 14.1 y | β-
IT | 0.580
0.264 | 113In
|
| 114Cd | 28.73% | Cd is stable with 66 neutrons |
| 116Cd | 7.49% | Cd is stable with 68 neutrons |
|
| SI units & STP are used except where noted. |
Cadmium is a
chemical element in the
periodic table that has the symbol Cd and
atomic number 48. A relatively rare, soft, bluish-white, toxic
transition metal, cadmium occurs with
zinc ores and is used largely in batteries.
Notable Characteristics
Cadmium is a soft, malleable, ductile, bluish-white bivalent metal which can be easily cut with a knife. It is similar in many respects to zinc but lends itself to more complex compounds.
The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.
Applications
About three-fourths of cadmium is used in |batteries (esp. Ni-Cd batteries) and most of the remaining one-fourth is used mainly for pigments, coatings and plating, and as stabilizers for plastics. Other uses;
- Used in some of the lowest melting alloys.
- Due to a low coefficient of friction and very good fatigue resistance, it is used in bearing alloys.
- 60% of cadmium finds use in electroplating.
- Many kinds of solder contain this metal.
- As a barrier to control nuclear fission.
- Compounds containing cadmium are used in black and white television phosphors and also in the blue and green phosphors for color television picture tubes.
- Cadmium forms various salts, with cadmium sulfate being the most common. This sulfide is used as a yellow pigment.
- Used in some semiconductors.
- Some cadmium compounds are employed in PVC as stabilizers.
History
Cadmium (Latin cadmia,
Greek kadmeia meaning "
calamine") was
discovered in
Germany in
1817 by Friedrich Stromeyer. Stromeyer found the new element within an impurity in zinc carbonate (calamine) and for 100 years Germany remained the only important producer of the metal. The metal was named after the Latin word for calamine since the metal was found in this zinc compound. Stromeyer noted that some impure samples of calamine changed color when heated but pure calamine did not.
Even though cadmium and its compounds are highly toxic, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medicine to treat "enlarged joints, scrofulous glands, and chilblains".
The International Conference on Weights and Measures in 1927 the redefined the meter in terms of a red cadmium spectral line (i.e. 1m = 1.553,164.13 wavelengths). This definition has since been changed (see krypton).
Occurrence
Cadmium-containing ores are rare and when found they occur in small quantities. Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnSS). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining sulfide ores of zinc, and to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap. Production in the United States began in 1907 but it was not until after World War I that cadmium came into wide use.
Isotopes
Naturally occurring cadmium is composed of 6 stable isotopes. 27 radioisotopes have been characterized with the most stable being Cd-113 with a half-life of 7.7 quadrillion years, Cd-109 with a half-life of 462.6 days, and Cd-115 with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lifes that are less than 2.5 hours and the majority of these have half lifes that are less than 5 minutes. This element also has 8 meta states with the most stable being Cdm-113 (t½ 14.1 years), Cdm-115 (t½ 44.6 days) and Cdm-117 (t½ 3.36 hours).
The isotopes of cadmium range in atomic weight from 96.935 amu (Cd-97) to 129.934 amu (Cd-138). The primary decay mode before the second most abundant stable-isotope, Cd-112, is electron capture and the primary mode after is beta emission. The primary decay product before Cd-112 is element 47 (silver) and the primary product after is element 49 (indium).
Precautions
Cadmium is one of the few elements that has no constructive purpose in the human body. This element and solutions of its compounds are extremely toxic even in low concentrations, and will bioaccumulate in organisms and ecosystems.
Inhaling cadmium laden dust quickly leads to respiratory tract and kidney problems which can be fatal (often from renal failure). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys. Compounds containing cadmium are also carcinogenic.
While working with cadmium it is important to do so under a fume hood to protect against dangerous fumes. Silver solder, for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths.
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