Cadmium Element Facts

48 Cd 112.41 Cadmium General | States | Energies Oxidation & Electrons | Appearance & Characteristics Reactions | Compounds | Radius | Conductivity Abundance & Isotopes Magnesium impurities in cadmium-selenium nanocrystals at two different gap levels: (a) resonant and (b) hybrid. (Photo: NERSC)

General:

Name: Cadmium	Symbol: Cd
Type: Transition Metal	Atomic weight: 112.41
Density @ 293 K: 8.65 g/cm3	Atomic volume: 13.1 cm3/mol
Discovered: Cadmium was discovered by Fredrich Stromeyer in 1817 as an impurity in zinc carbonate (ZnCO3, calamine). He observed that some impure samples of calamine changed color when heated, but pure calamine did not. The element name comes from the Latin word 'cadmia', meaning calamine.

States

State (s, l, g): solid
Melting point: 594.3 K   (321.1 oC)	Boiling point: 1038 K   (765 oC)

Energies

Specific heat capacity: 0.23 J g-1 K-1	Heat of atomization: 112 kJ mol-1
Heat of fusion: 6.192 kJ mol-1	Heat of vaporization : 99.87 kJ mol-1
1st ionization energy: 867.7 kJ mol-1	2nd ionization energy: 1631.4 kJ mol-1
3rd ionization energy: 3616.2 kJ mol-1	Electron affinity: kJ mol-1

Oxidation & Electrons

Shells: 2,8,18,18,2	Electron configuration: [Kr] 4d10 5s2
Minimum oxidation number: 0	Maximum oxidation number: 2
Min. common oxidation no.: 0	Max. common oxidation no.: 2
Electronegativity (Pauling Scale): 1.69	Polarizability volume: 7.2 Å3

Appearance & Characteristics

Structure: hcp (hexagonal close-packed)	Color: bluish-white
Hardness: 2.0 mohs
Harmful effects: Cadmium and its compounds are highly toxic.
Characteristics: Cadmium is a soft, malleable, ductile, bluish-white metal, which is easily cut with a knife. It is an excellent electrical conductor and shows good resistance to corrosion and attack by chemicals. It is similar in many respects to zinc in its chemical properties. Cadmium tarnishes in air and is soluble in acids but not in alkalis. The metal burns in air to form brown cadmium oxide (CdO).
Uses: Most cadmium is used in batteries (especially rechargeable nickel-cadmium, NiCad, batteries). As a result of its low coefficient of friction and its high fatigue resistance, cadmium is used in alloys for bearings. Cadmium is used in low melting alloys and is a component of many kinds of solder. It is also is used in electroplating. Compounds containing cadmium are used in black and white television phosphors, and in the blue and green phosphors for color television picture tubes. Cadmium sulfide is used as a yellow pigment, and cadmium selenide is used as a red pigment, often called cadmium red. Cadmium and tellurium can be compounded into CdTe thin-film photovoltaic modules whose physical characteristics are ideal for solar cell production. They are relatively low cost and have an almost perfect bandgap for solar energy harvesting. (Image left credit: NREL)

Reactions

Reaction with air: mild, w/ht ⇒ CdO	Reaction with 6 M HCl: mild, ⇒ H2, CdCl2
Reaction with 15 M HNO3: mild ⇒ Cd(NO3)2, NOx	Reaction with 6 M NaOH: none

Compounds

Oxide(s): CdO, CdO2	Chloride(s): CdCl2
Hydride(s): CdH2

Radius

Atomic radius: 151 pm	Ionic radius (1+ ion): pm
Ionic radius (2+ ion): 109 pm	Ionic radius (3+ ion): pm
Ionic radius (2- ion): pm	Ionic radius (1- ion): pm

Conductivity

Thermal conductivity: 96.6 W m-1 K-1

Electrical conductivity: 14.7 x 106 S m-1

Abundance & Isotopes

Abundance earth's crust: 150 parts per billion by weight, 30 parts per billion by moles

Abundance solar system: 6 parts per billion by weight, 70 parts per trillion by moles

Cost, pure: $6 per 100g

Cost, bulk: $ per 100g

Source: Cadmium most often occurs in small quantities associated with zinc ores, such as sphalerite (ZnS). Greenockite (CdS) is the only cadmium mineral of any consequence. Almost all cadmium is obtained as a by-product of zinc, copper, and lead ore refining operations.

Isotopes: Cadmium has 34 isotopes whose half-lives are known, with mass numbers from 97 to 130. Of these, seven are stable: 106Cd, 108Cd, 110Cd, 111Cd, 112Cd, 114Cd and 116Cd. Naturally, the most abundant isotope is 114Cd at 28.7%.