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Cadmium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                48                silver ← cadmium → indium
                Zn
                ↑
                Cd
                ↓
                Hg

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                      Name, Symbol, Number cadmium, Cd, 48
                                         Chemical series transition metals
                                             Group, Period, Block 12, 5, d
                                          Appearance silvery gray metallic
                                             Atomic mass 112.411 (8) g/mol
                                    Electron configuration [Kr] 4d^10 5s^2
                                       Electrons per shell 2, 8, 18, 18, 2
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 8.65 g·cm^−3
                                   Liquid density at m.p. 7.996 g·cm^−3
                                                   Melting point 594.22  K
                                                (321.07 ° C, 609.93 ° F)
                                                      Boiling point 1040 K
                                                     (767 ° C, 1413 ° F)
                                          Heat of fusion 6.21 kJ·mol^−1
                                   Heat of vaporization 99.87 kJ·mol^−1
                         Heat capacity (25 °C) 26.020 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                          P/Pa   1  10  100 1 k 10 k 100 k
                                         at T/K 530 583 654 745 867  1040

                                                         Atomic properties
                                               Crystal structure hexagonal
                                                        Oxidation states 2
                                                      (mildly basic oxide)
                                    Electronegativity 1.69 (Pauling scale)
                                     Ionization energies 1st: 867.8 kJ/mol
                                                        2nd: 1631.4 kJ/mol
                                                          3rd: 3616 kJ/mol
                                                      Atomic radius 155 pm
                                              Atomic radius (calc.) 161 pm
                                                    Covalent radius 148 pm
                                               Van der Waals radius 158 pm
                                                             Miscellaneous
                                                 Magnetic ordering no data
                               Electrical resistivity (22 °C) 72.7 nΩ·m
                       Thermal conductivity (300 K) 96.6 W·m^−1·K^−1
                       Thermal expansion (25 °C) 30.8 µm·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 2310 m/s
                                                    Young's modulus 50 GPa
                                                      Shear modulus 19 GPa
                                                       Bulk modulus 42 GPa
                                                        Poisson ratio 0.30
                                                         Mohs hardness 2.0
                                                  Brinell hardness 203 MPa
                                             CAS registry number 7440-43-9
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of cadmium

                          iso      NA    half-life    DM  DE ( MeV)   DP
                        ^106Cd   1.25%  >9.5×10^17 y εε2ν -         ^106Pd
                        ^108Cd   0.89%  >6.7×10^17 y εε2ν -         ^108Pd
                        ^109Cd   syn    462.6 d      ε    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   12.22% 7.7×10^15 y  β^-  0.316     ^113In
                        ^113 mCd syn    14.1 y       β^-  0.580     ^113In
                                                     IT   0.264     ^113Cd
                        ^114Cd   28.73% >9.3×10^17 y ββ2ν -         ^114Sn
                        ^116Cd   7.49%  2.9×10^19 y  ββ2ν -         ^116Sn

                                                                References

   Cadmium ( IPA: /ˈkadmiəm/) is a chemical element in the periodic table
   that has the symbol Cd and atomic number 48. A relatively rare, soft,
   bluish-white, transition metal, cadmium is known to cause cancer and
   occurs with zinc ores. Cadmium is used largely in batteries.

Production

   Cadmium is a common impurity in zinc, and it is most often isolated
   during the production of zinc. Zinc sulfide ores are roasted in the
   presence of oxygen converting the zinc sulfide to the oxide. Zinc metal
   is produced either by smelting the oxide with carbon or by electrolysis
   in sulfuric acid. Cadmium is isolated from the zinc metal by vacuum
   distillation if the zinc is smelted, or cadmium sulfate is precipitated
   out of the electrolysis solution.

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 reacts to form 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 (especially 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.
     * 6% 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 colour
       television picture tubes.
     * Cadmium forms various salts, with cadmium sulfide being the most
       common. This sulfide is used as a yellow pigment. Cadmium selenide
       can be used as red pigment, commonly called cadmium red. To
       painters who work with the pigment, Cadmium yellows, oranges and
       reds are the most potent colours to use. In fact,during production
       these colours are significantly toned down before they are ground
       with oils and binders, or blended into watercolours, gouaches,
       casesin, acrylics and other paint and pigment formulations. These
       pigments are toxic and it is recommended to use a barrier cream on
       your hands to prevent absorption through the skin when working with
       them. There is no such thing as cadmium blue, green or violet.
     * Used in some semiconductors such as cadmium sulfide, cadmium
       selenide, and cadmium telluride, which can be used for light
       detection or solar cells. HgCdTe is sensitive to infrared.
     * Some cadmium compounds are employed in PVC as stabilizers.
     * Used in the first neutrino detector.
     * Used to block voltage-dependent calcium channels from fluxing
       calcium ions in molecular biology.

History

   Cadmium (Latin cadmia, Greek kadmeia meaning " calamine") was
   discovered in Germany in 1817 by Friedrich Strohmeyer. Strohmeyer 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. Strohmeyer noted that some impure
   samples of calamine changed colour 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".

   In 1927, the International Conference on Weights and Measures redefined
   the meter in terms of a red cadmium spectral line (1m = 1,553,164.13
   wavelengths). This definition has since been changed (see krypton).

Occurrence

   Cadmium metal
   Enlarge
   Cadmium metal

   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 (ZnS). 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

   Image of the violet light from a helium cadmium metal vapor laser. The
   highly monochromatic color arises from the 441.563 nm transition line
   of cadmium.
   Enlarge
   Image of the violet light from a helium cadmium metal vapor laser. The
   highly monochromatic colour arises from the 441.563 nm transition line
   of cadmium.

   Naturally occurring cadmium is composed of 8 isotopes. For two of them,
   natural radioactivity was observed, and other three are predicted to be
   radioactive but their decays were never observed, due to extremely long
   half-life times. The two natural radioactive isotopes are ^113Cd ( beta
   decay, half-life is 7.7 X 10^15 years) and ^116Cd (two-neutrino double
   beta decay, half-life is 2.9 X 10^19 years). Other three ones are
   ^106Cd, ^108Cd ( double electron capture), and ^114Cd ( double beta
   decay); only lower limits on their half-life times have been set. At
   least three isotopes - ^110Cd, ^111Cd, and ^112Cd - are absolutely
   stable. Among the isotopes absent in the natural cadmium, the most
   long-lived are ^109Cd with a half-life of 462.6 days, and ^115Cd 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
   known meta states with the most stable being ^113mCd (t[½] 14.1 years),
   ^115mCd (t[½] 44.6 days) and ^117mCd (t[½] 3.36 hours).

   The known isotopes of cadmium range in atomic weight from 96.935 u
   (^97Cd) to 129.934 amu (^138Cd). The primary decay mode before the
   second most abundant stable isotope, ^112Cd, is electron capture and
   the primary modes after are beta emission and electron capture. The
   primary decay product before ^112Cd is element 47 (silver) and the
   primary product after is element 49 (indium).

Precautions

   Cadmium is toxic
   Enlarge
   Cadmium is toxic

   Cadmium has no constructive purpose in the human body. This element and
   solutions of its compounds are toxic even in low concentrations, and
   will bioaccumulate in organisms and ecosystems. Chronic poisoning by
   cadmium is called Itai-itai disease. One possible reason for its
   toxicity is that it interferes with the action of zinc-containing
   enzymes. Zinc is an important element in biological systems, but
   cadmium, although similar to zinc chemically in many ways, apparently
   does not substitute or "stand in" for it well at all. Cadmium may also
   interfere with biological processes containing magnesium and calcium in
   a similar fashion. Pathways of human contact include soil contamination
   from industrial releases or landfill and associated leachate processes.

   Inhaling cadmium laden dust quickly leads to respiratory tract
   infection 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 , and can induce
   many types of cancer .

   Cadmium poisoning is the cause of the itai-itai disease, which
   literally means "ouch ouch" in Japanese. In addition to kidney damage,
   patients suffered from osteoporosis and osteomalacia.

   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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