Cadmium
[Kr] 4d¹⁰ 5s² · 2 · 8 · 18 · 18 · 2
A soft white metal chemically close to zinc and far more poisonous. Cadmium gave its name to one of history's worst mass poisonings and has been designed out of most applications on environmental grounds.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 48
- Atomic mass
- 112.414 а.е.м.
- Electron configuration
- [Kr] 4d¹⁰ 5s²
- Electrons per shell
- 2 · 8 · 18 · 18 · 2
- Block
- d-block
- Group
- Zinc group
- Period
- 5
- Electronegativity (Pauling)
- 1.69
- Electronegativity (Allen)
- 1.52
- Atomic radius
- 161 pm
- Covalent radius
- 144 pm
- Van der Waals radius
- 158 pm
- Ionisation energy 1
- 867.8 kJ/mol
- Ionisation energy 2
- 1 631.4 kJ/mol
- Ionisation energy 3
- 3 616 kJ/mol
- Electron affinity
- 0 kJ/mol
- Common oxidation states
- +2
- Oxidation states
- -2, +1, +2
Physical properties
- State at 25 °C
- solid
- Density
- 8.65 g/cm³
- Melting point
- 594.22 K · 321.1 °C
- Boiling point
- 1 040 K · 766.9 °C
- Speed of sound
- 2 310 m/s
Thermal properties
- Heat of fusion
- 6.21 kJ/mol
- Heat of vaporisation
- 99.87 kJ/mol
- Specific heat capacity
- 0.232 J/(g·K)
- Thermal conductivity
- 96.6 W/(m·K)
Mechanical properties
- Young's modulus
- 50 GPa
- Shear modulus
- 19 GPa
- Bulk modulus
- 42 GPa
- Poisson ratio
- 0.3
- Mohs hardness
- 2
- Brinell hardness
- 203 MPa
Electrical and magnetic properties
- Electrical resistivity
- 72.7 nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 0.517 K
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 297.94 pm · c = 561.86 pm
Abundance
- In the crust
- 0.15 mg/kg
- In the ocean
- 0.00011 mg/L
- In the universe
- 0.2 mg/kg
- In the human body
- 0.7 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 106Cd | 1.25 % | stable | — |
| 108Cd | 0.89 % | stable | — |
| 110Cd | 12.49 % | stable | — |
| 111Cd | 12.8 % | stable | — |
| 112Cd | 24.13 % | stable | — |
| 113Cd | 12.22 % | 7.922·10⁶ Gyr | β− |
| 114Cd | 28.73 % | stable | — |
| 116Cd | 7.49 % | stable | — |
Cadmium-113 has an exceptionally large thermal neutron capture cross-section, which is exactly why cadmium goes into control rods.
Discovery
- Year of discovery
- 1817
- Discovered by
- Friedrich Stromeyer
- Where
- Germany
- Origin of the name
- from Latin cadmia, the zinc ore it was found in
History
Friedrich Stromeyer examined a batch of zinc carbonate that yellowed on heating in 1817 and found a new element in it. The name is from Latin cadmia, the old word for zinc ore.
Where it occurs
0.15 mg/kg of the crust. It has essentially no ores of its own and always accompanies zinc in sphalerite.
How it is produced
Solely as a by-product of zinc production, from dusts and residues.
Role in living things
No biological role. Cadmium displaces zinc from enzymes and accumulates in the kidneys, where its biological half-life runs to decades.
Safety
A Group 1 carcinogen. Itai-itai disease in 1940s Japan was mass cadmium poisoning from rice paddies irrigated with mine effluent, marked by multiple bone fractures and pain at the slightest movement.
Uses
- Nickel-cadmium batteries (restricted in the EU)
- Cadmium telluride in thin-film solar modules
- Pigments: cadmium yellow, orange and red
- Nuclear reactor control rods
- Anti-corrosion plating in aerospace
Curiosities
- Itai-itai in Japanese means literally "it hurts, it hurts".
- Cadmium pigments gave painters their most brilliant yellows and reds, but are now largely displaced.
- A smoker takes in about twice as much cadmium as a non-smoker: tobacco concentrates the metal from soil.
- Cadmium-113 absorbs neutrons twenty thousand times more readily than natural boron.