48
  Cd  
112.411000
Cadmium

Name: Cadmium
Symbol: Cd
Atomic Number: 48
AtomicWeight: 112.411000
Family:
CAS RN: 7440-43-9
Description: A soft, bluish-white metal.
State (25 C): Solid
Oxidation states: +2

Molar Volume: 13.01 cm3/mole
Valence Electrons: 5s2

Boiling Point:  1038K, 765C, 1409F
Melting Point:
594.33K, 321.18C, 610.12F
Electrons Energy Level: 2, 8, 18, 18, 2
Isotopes: 32 (30) + 6 (8) Stable
Heat of Vaporization: 99.57 kJ/mol
Heat of Fusion: 6.192 kJ/mol
Density: 8.65 g/cm3 @ 300K
Specific Heat: 0.231 J/gK
Atomic Radius: 1.71
Ionic Radius: 0.97
Electronegativity: 1.69 (Pauling); 1.46 (Allrod Rochow)
Vapor Pressure: 14.8 Pa @ 321.18C

1s2 2s2p6 3s2p6d10 4s2p6d10 5s2

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 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".

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.

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.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10
5s2

The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.

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 (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.

A role of cadmium in biology has been recently discovered.  A cadmium-dependent carbonic anhydrase has been found in marine diatoms.  Cadmium does the same job as zinc in other anhydrases, but the diatoms live in environments with very low zinc concentrations, thus biology has taken cadmium rather than zinc, and made it work.   The discovery was made using x-ray absorption fluoresence spectroscopy (XAFS), and cadmium was characterised by noting the energy of the x-rays which were absorbed.

Applications

About three-quarters of cadmium is used in batteries (especially Ni-Cd batteries) and most of the remaining quarter is used mainly for pigment, coatings and plating, and as stabilizers for platics.  Other uses include:

Hydrated cadmium sulfate (3CdSO45H2O), one of cadmium's compounds, is used in a device called a Weston cell, a type of battery that produces a precise voltage used to calibrate medical and laboratory equipment.  Cadmium sulfide (CdS), another cadmium compound, is a yellow powder that is used as a pigment.  Other cadmium compounds are used in the phosphors of black and white television sets and in the blue and green phosphors in color television sets.

Extraction

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.

Compounds

Cadmium Iodide, CdI2 Greenockite, Cadmium Sulfide, CdS
Cadmium Sulfate, 3CdSO45H2O

Isotopes

Naturally occurring cadmium is composed of 8 isotopes.  For two of them, natural radioactivity was observed, and three others 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 1015 years) and 116Cd (two-neutrino double beta decay, half-life is 2.9 X 1019 years).  The other three 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-lives that are less than 2.5 hours and the majority of these have half-lives that are less than 5 minutes.  This element also has 8 known meta states with the most stable being 113mCd (t 14.1 years), 115mCd (t 44.6 days) and 117mCd (t 3.36 hours).

The known isotopes of cadmium range in atomic mass from 94.950 u (95Cd) to 131.946 u (132Cd).  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).

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Isotope  
Atomic Mass
 
Half-Life
95Cd 94.94987 ~5 ms
96Cd 95.93977 ~1 seconds
97Cd 96.93494 2.8 seconds
98Cd 97.92740 9.2 seconds
99Cd 98.92501 16 seconds
100Cd 99.92029 49.1 seconds
101Cd 100.91868 1.36 minutes
102Cd 101.91446 5.5 minutes
103Cd 102.913419 7.3 minutes
104Cd 103.909849 57.7 minutes
105Cd 104.909468 55.5 minutes
106Cd 105.906459 Stable
107Cd 106.906618 6.50 hours
108Cd 107.904184 Stable
109Cd 108.904982 461.4 days
110Cd 109.9030021 Stable
111Cd 110.9041781 Stable
112Cd 111.9027578 Stable
113Cd 112.9044017 7.7 x 1015 years
114Cd 113.9033585 Stable
115Cd 114.9054310 53.46 hours
116Cd 115.904756 3.1 x 1019 years
117Cd 116.907219 2.49 hours
118Cd 117.906915 50.3(2) minutes
119Cd 118.90992 2.69 minutes
120Cd 119.90985 50.80 seconds
121Cd 120.91298 13.5 seconds
122Cd 121.91333 5.24 seconds
123Cd 122.91700 2.10 seconds
124Cd 123.91765 1.25 seconds
125Cd 124.92125 0.65 seconds
126Cd 125.92235 0.515 seconds
127Cd 126.92644 0.37 seconds
128Cd 127.92776 0.28 seconds
129Cd 128.93215 242 ms
130Cd 129.9339 162 ms
131Cd 130.94067 68 ms
132Cd 131.94555 97 ms

Precautions

80px-Flammable.jpg (2186 bytes) While working with cadmium it is important to do so under a fume hood or with the use of an appropriate respirator to protect against dangerous fumes.  Solder, for example, which may contain cadmium, should be handled with care.

Cadmium is an occupational hazard associated with industrial processes such as metal plating and the production of nickel-cadmium batteries, pigments, plastics and other synthetics.  The primary route of exposure in industrial settings is inhalation.   Inhalation of cadmium-containing fumes can result initially in metal fume fever but may progress to chemical pneumonitis, pulmonary edema, and death.

Cadmium is also a potential environmental hazard.  Human exposures to environmental cadmium are primarily the result of the burning of fossil fuels and municipal wastes.  However, there have been notable instances of toxicity as the result of long-term exposure to cadmium in contaminated food and water.  In the decades following World War II, Japanese mining operations contaminated the Jinzu River with cadmium and traces of other toxic metals.  Consequently, cadmium accumulated in the rice crops growing along the riverbanks downstream of the mines.  The local agricultural communities consuming the contaminated rice developed Itai-itai disease and renal abnormalities, including proteinuria and glucosuria.

40px-Skull_and_crossbones.svg.jpg (1420 bytes) Cadmium and several cadmium-containing compounds are known carcinogens and can induce many types of cancer.

The mechanism of cadmium toxicity has not been established. 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.

atom.gif (700 bytes)

Cadmium Data
 

Atomic Structure

  • Atomic Radius: 1.71
  • Atomic Volume: 13.1cm3/mol
  • Covalent Radius: 1.48
  • Cross Section (Thermal Neutron Capture) Barns: 2450
  • Crystal Structure: Hexagonal
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10 5s2
  • Electrons per Energy Level: 2, 8, 18, 18, 2
  • Ionic Radius: 0.97
  • Filling Orbital: 4d10
  • Number of Electrons (with no charge): 48
  • Number of Netrons (most common/stable nuclide): 64
  • Number of Protons: 48
  • Oxidation States: 2
  • Valence Electrons: 5s2

Chemical Properties

  • Electrochemical Equivalent: 2.097 g/amp-hr
  • Electron Work Function: 4.22eV
  • Electronegativity: 1.69 (Pauling); 1.46 (Allrod Rochow)
  • Heat of Fusion: 6.192 kJ/mol
  • Incompatibilities:
    strong oxidizers, ammonium nitrate, hydrazoic acid, tellurium, zinc, elemental sulfur, selenium
  • Ionization Potential
    • First: 8.993
    • Second: 16.908
    • Third: 37.48
  • Valence Electron Potential (-eV): 30

Physical Properties

  • Atomic Mass Average: 112.411
  • Boiling Point: 1038K, 765C, 1409F
  • Coefficient of Lineal Thermal Expansion/K-1: 29.8E-6
  • Conductivity
    Electrical: 0.138 106/cm
    Thermal: 0.968 W/cmK
  • Density: 8.65 g/cm3 @ 300K
  • Description:
    Silvery white transition metal.
  • Elastic Modulus:
    • Bulk: 42/GPa
    • Rigidity: 19/GPa
    • Youngs: 50/GPa
  • Enthalpy of Atomization: 113 kJ/mole @ 25C
  • Enthalpy of Fusion: 6.19 kJ/mole
  • Enthalpy of Vaporization: 100 kJ/mole
  • Flammablity Class: Non-combustible solid (except as dust)
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 203 MN m-2
    • Mohs: 2
  • Heat of Vaporization: 99.57 kJ/mol
  • Melting Point: 594.33K, 321.18C, 610.12F
  • Molar Volume: 13.01 cm3/mole
  • Optical Reflectivity: 67%
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.231 J/gK
  • Vapor Pressure: 14.8 Pa @ 321.18C

Regulatory / Health

  • CAS Number
    • 7440-43-9 compounds
  • UN/NA ID and ERG Guide Number
    • 2570  / 154 compounds
  • RTECS: EU9800000
  • OSHA Permissible Exposure Limit (PEL)
    • TWA: 0.005 mg/m3
  • OSHA PEL Vacated 1989
    • TWA: 0.005 mg/m3
  • NIOSH Recommended Exposure Limit (REL)
    • IDLH:  9 mg/m3 (Potential NIOSH carcinogen)
  • Routes of Exposure: Inhalation; Ingestion
  • Target Organs: Respiratory system, kidneys, prostate, blood
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: 0.0052
    • Bone/p.p.m: 1.8
    • Liver/p.p.m: 2-22
    • Muscle/p.p.m: 0.14-3.2
    • Daily Dietary Intake: 0.007-3 mg
    • Total Mass In Avg. 70kg human: 50 mg

Who / Where / When / How

  • Discoverer: Fredrich Stromeyer
  • Discovery Location: Gttingen Germany
  • Discovery Year: 1817
  • Name Origin:
    Greek: kadmeia (ancient name for calamine, ZnCO3); Latin: cadmia.
  • Abundance:
    • Earth's Crust/p.p.m.: 0.11
    • Seawater/p.p.m.:
      • Atlantic Suface: 0.0000011
      • Atlantic Deep: 0.000038
      • Pacific Surface: 0.0000011
      • Pacific Deep: 0.0001
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 71
  • Sources:
    Obtained as a by product of zinc refining. Annual world production is around 13,900 tons.
  • Uses:
    Used in nickel-cadmium batteries, nuclear reactor regulator, and red/yellow pigments.
  • Additional Notes:
    While cadmium is toxic, fatal poisonings rarely occur because of its emetic action, which means little is absorbed.

Ionization Energy (eV): 8.994 eV
Estimated Crustal Abundance: 1.510-1 milligrams per kilogram
Estimated Oceanic Abundance:
1.110-4 milligrams per liter

Transition Metals
Group 3
(IIIB)
4
(IVB)
5
(VB)
6
(VIB)
7
(VIIB)
8
(VIIIB)
9
(VIIIB)
10 (VIIIB) 11
(IB)
12
(IIB)
Period 4 21
Sc
44.95
22
Ti
47.86
23
V
50.94
24
Cr
51.99
25
Mn
54.93
26
Fe
55.84
27
Co
58.93
28
Ni
58.69
29
Cu
63.54
30
Zn
65.39
Period 5 39
Y
88.90
40
Zr
91.22
41
Nb
92.90
42
Mo
95.94
43
Tc
98.00
44
Ru
101.0
45
Rh
102.9
46
Pd
106.4
47
Ag
107.8
48
Cd
112.4
Period 6 57
La
138.9
72
Hf
178.4
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.0
79
Au
196.9
80
Hg
200.5
Period 7 89
Ac
227.0
104
Rf
261.0
105
Db
262.0
106
Sg
266.0
107
Bh
264.0
108
Hs
269.0
109
Mt
268.0
110
Ds
269.0
111
Rg
272.0
112
Uub
277.0