Quick Facts
| Property | Value |
|---|---|
| Symbol | Cd |
| Atomic Number | 48 |
| Atomic Mass | 112.41 u |
| Category | Transition Metal |
| Period | 5 |
| Group | 12 |
| Block | d |
| Electron Configuration | [Kr] 4d¹⁰ 5s² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 8.65 g/cm³ |
| Melting Point | 321.07°C (594.22 K) |
| Boiling Point | 767°C (1040 K) |
| Appearance | Silvery-white, bluish tinge |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Kr] 4d¹⁰ 5s² |
| Electronegativity | 1.69 (Pauling scale) |
| First Ionization Energy | 867.8 kJ/mol |
| Atomic Radius | 151 pm |
| Covalent Radius | 144 pm |
| Van der Waals Radius | 158 pm |
History and Discovery
Discovered by: Karl Samuel Leberecht Hermann and Friedrich Stromeyer Year of Discovery: 1817 Location: Germany
Etymology
Named from "cadmia," the Latin name for calamine (zinc carbonate ore), from which cadmium was first isolated as an impurity.
Discovery Story
Friedrich Stromeyer discovered cadmium in 1817 while investigating an impurity in zinc carbonate. Karl Hermann independently discovered it around the same time. Both found it as a yellowish impurity in zinc oxide that turned out to be a new element.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ¹⁰⁶Cd | 1.25% | Stable | - |
| ¹⁰⁸Cd | 0.89% | Stable | - |
| ¹¹⁰Cd | 12.49% | Stable | - |
| ¹¹¹Cd | 12.80% | Stable | - |
| ¹¹²Cd | 24.13% | Stable | - |
| ¹¹³Cd | 12.22% | 8.04 × 10¹⁵ years | β⁻ |
| ¹¹⁴Cd | 28.73% | Stable | - |
| ¹¹⁶Cd | 7.49% | 2.9 × 10¹⁹ years | β⁻β⁻ |
Occurrence
Natural Abundance
Cadmium is relatively rare, comprising about 0.15 ppm of Earth's crust. It is almost always found associated with zinc ores (sphalerite contains 0.1-0.3% Cd). Major producers are China, South Korea, and Japan.
Extraction and Production
- Byproduct: Almost entirely from zinc refining
- Electrolytic: Recovered from zinc electrolysis
- Sources: Zinc smelting operations
- Global production: about 25,000 tons annually
Applications and Uses
Batteries
- Nickel-cadmium (NiCd) rechargeable batteries (declining use)
- Industrial applications
- Emergency power systems
Coatings
- Corrosion-resistant electroplating (declining)
- Aerospace applications
- Marine hardware
Pigments
- Cadmium yellow, orange, and red (artist paints)
- Plastics (being phased out)
Other Uses
- Nuclear reactor control rods (cadmium absorbs neutrons)
- Cadmium telluride solar cells
- Specialty alloys
Biological Role
Cadmium has no beneficial biological role and is highly toxic to most organisms.
In the Human Body
Cadmium accumulates in the body, particularly in kidneys and liver. The biological half-life is 10-30 years.
Toxicity
Cadmium is one of the most toxic heavy metals. It causes kidney damage, bone disease (itai-itai disease), and cancer.
Safety and Hazards
Toxicity
Cadmium is extremely toxic. It causes kidney damage, bone demineralization, and is a known carcinogen. Chronic exposure leads to serious health effects.
Handling Precautions
- Avoid inhalation of dust or fumes
- Use appropriate PPE
- Proper ventilation essential
- Known human carcinogen (Group 1)
- Strict regulations on use and disposal
Environmental Impact
Cadmium persists in the environment and bioaccumulates. Mining, smelting, and improper battery disposal are major sources of contamination.
Interesting Facts
- Itai-itai disease in Japan (1950s) was caused by cadmium-contaminated rice
- Cadmium's use is declining due to environmental concerns
- Cadmium yellow was a favorite pigment of Claude Monet
- Cadmium-113 has an exceptionally high neutron absorption cross-section
- The EU has banned cadmium in most consumer products