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Cadmium (Cd)

QUICK REFERENCE

  • Symbol: Cd
  • Atomic Number: 48
  • Atomic Weight: 112.414
  • Element Classification: Transition Metal
  • Discovered By: Friedrich Stromeyer
  • Discovery Date: 1817
  • Name Origin: From the Latin ‘cadmia’ and the Greek ‘kadmeia’, ancient names for calamine (zinc carbonate), because it was discovered in this zinc compound
  • Density(g/cc): 8.65
  • Melting Point: 321.07°C
  • Boiling Point: 767°C
  • Appearance: Silvery-white, malleable, ductile metal
  • Atomic Radius(pm): 151

Discovery

Cadmium was discovered by German chemist Friedrich Stromeyer in 1817 while he was examining zinc carbonate samples. Stromeyer noticed that some samples turned yellow when heated, unlike pure zinc carbonate, which led him to investigate further. He eventually isolated cadmium, recognizing it as a new element. The discovery was confirmed by another chemist, Karl Samuel Leberecht Hermann, who also found the element independently in the same year.

Relation to Other Elements

Cadmium is a transition metal, located in group 12 of the periodic table, alongside zinc and mercury. Like zinc, it prefers to form +2 oxidation state compounds. Cadmium shares physical and chemical properties with zinc and mercury, including its reactivity and the ability to form complex compounds. However, cadmium is less abundant than zinc and is known for its toxicity to living organisms.

Natural Occurrence

Cadmium is not found free in nature but is most often encountered as a minor component in zinc ores, such as sphalerite (ZnS). The metal is obtained as a byproduct of zinc smelting and refining. It is relatively rare, with concentrations in the Earth’s crust estimated to be about 0.1 to 0.5 parts per million, making it about as abundant as silver.

Uses

Despite its toxicity, cadmium has several important applications:

  • Batteries: Cadmium is used in nickel-cadmium (NiCd) rechargeable batteries, appreciated for their high electrical conductivity and ability to deliver a stable current over a long period.
  • Pigments: Cadmium compounds are used to create vibrant red, yellow, and orange pigments for ceramics, glass, and plastics.
  • Coatings: Cadmium plating is applied to steel to protect against corrosion in marine and alkaline environments.
  • Stabilizers: In plastics manufacturing, cadmium stabilizers are added to PVC to enhance its heat and light stability.
  • Control Rods in Nuclear Reactors: Cadmium is utilized in control rods for nuclear reactors due to its ability to absorb neutrons.

The discovery of cadmium filled a niche in materials science, particularly in battery technology and pigments. However, due to its adverse health and environmental impacts, the use of cadmium is being reduced, and alternatives are being sought for many of its applications.

 

Silver (Ag)

Indium (In)