Cadmium is a metallic element with atomic number 48 and element symbol Cd on the periodic table. It occurs in batteries, paints and pigments, plastics, and solar panels. However, because cadmium is toxic and carcinogenic, its uses are decreasing. Here is a collection of cadmium facts, including its properties, toxicity, uses, and sources.
Basic Cadmium Facts
- Name: Cadmium
- Atomic Number: 48
- Element Symbol: Cd
- Atomic Mass: 112.414
- Group: 12 (zinc group)
- Period: 5
- Block: d-block
- Electron Configuration: [Kr] 4d10 5s2
- Appearance: Soft, silvery-blue metal
Friedrich Stromeyer and Karl Samuel Leberecht Hermann independently discovered cadmium in 1817. Stromeyer found the metal as a contamination in zinc compounds being sold in pharmacies, while Hermann discovered the element as a discoloration in a zinc chloride sample.
The name “cadmium” refers to the Greek word for calamine, which is a zinc ore that contains the metal. Calamine, in turn, takes its name for the Greek mythology character Cadmus, who was the founder of Thebes.
Cadmium Toxicity and Poisoning
Cadmium serves no known biological role in humans and most other species. The exception is a cadmium-dependent enzyme found in certain marine diatoms. In humans, cadmium is a pollutant and toxin that causes oxidative stress. Exposure, usually through inhalation or ingestion, increases risks of cardiovascular disease, cancer, and osteoporosis. The kidneys preferentially absorb the metal, so exposure often causes damage. Inhalation causes metal fume fever, which sometimes leads to pulmonary edema and death.
Occurrence and Production
Cadmium accounts for about 0.1 ppm of the Earth’s crust. It almost always occurs with zinc and is obtained as a by-product of zinc mining and purification. Sometimes lead and copper ores also contain cadmium. Phosphate fertilizer, coal, and soil often contain significant amounts of the element. Sources include recycling of iron and steel scrap or from mining in China, South Korea, Japan, the United States, and Siberia in Russia.
Natural cadmium consists of a mixture of either isotopes. Two of these isotopes are radioactive. The isotopes range from Cd-95 to Cd-132.
Cadmium is important for electric batteries, solar cells, pigments, electroplating, coatings, nuclear reactor control rods, QLED televisions, semiconductors, and certain anticancer drugs. As a plating, cadmium reduces steel corrosion. Common pigments include cadmium selenide (cadmium red) and cadmium sulfide (cadmium yellow). Cadmium also finds uses as a stabilizer in plastics and for the manufacture of helium-cadmium lasers.
Density: 8.65 g/cm3
Melting Point: 594.22 K (321.07 °C, 609.93 °F)
Boiling Point: 1040 K (767 °C, 1413 °F)
State at 20ºC: Solid
Heat of Fusion: 6.21 kJ/mol
Heat of Vaporization: 99.87 kJ/mol
Molar Heat Capacity: 26.020 J/(mol·K)
Atomic Radius: 151 pm
Covalent Radius: 144±9 pm
Van der Waals Radius: 158 pm
Crystal Structure: hexagonal close-packed (hcp)
Young’s modulus: 50 Gpa
Shear modulus: 19 GPa
Bulk modulus: 42 GPa
Poisson ratio: 0.30
Mohs hardness: 2.0
Electronegativity: 1.69 (Pauling scale)
1st Ionization Energy: 867.8 kJ/mol
2nd Ionization Energy: 1631.4 kJ/mol
3rd Ionization Energy: 3616 kJ/mol
Oxidation States: -2, +1, +2
Interesting Cadmium Facts
- With a Mohs hardness of 2, cadmium is so soft you can scratch it with a fingernail.
- Like most metals, cadmium is highly malleable and ductile.
- While not generally flammable, powdered cadmium burns and releases toxic vapor.
- Mostly, chemists classify cadmium as a transition metal. However, because if does not have a partly-filled d or f shell, some scientists classify it as a member of the zinc group and not, technically, a transition metal.
- Cadmium, like its congeners zinc and mercury, has a lower melting point than most transition metals.
- Low-mass and medium-mass stars make cadmium via the S-process from silver atoms.
- Cadmium, like lead, is a heavy metal. Because of its toxicity, many countries regulate the supply and use of cadmium.
- One source of cadmium poisoning in children is cheap jewelry, as kids sometimes put items in their mouths. Cadmium paints on toys or glassware also lead to problems.
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