Cadmium
Element 48 · Transition Metal
Cadmium is a soft metal that sits at the end of the transition series with a full d-shell, so its chemistry is simple — it almost always forms the Cd²⁺ ion. It found wide use in nickel-cadmium rechargeable batteries, vivid artists' pigments, and protective plating. But cadmium is also seriously toxic: it accumulates in the kidneys and bones, and its most infamous poisoning episode, itai-itai disease in Japan, came from cadmium-polluted rice. Because of this, regulations now restrict cadmium in electronics and consumer goods, and NiCd batteries are being replaced by safer chemistries.
Key facts
| Atomic number | 48 |
|---|---|
| Atomic weight | 112.41 |
| Category | Transition Metal |
| Group / Period | 12 / 5 |
| Block | d |
| Electron configuration | [Kr] 4d10 5s2 |
| Common oxidation states | +2 |
| State at STP | Solid |
| Electronegativity | 1.69 |
| Atomic radius | 151 pm (empirical) |
| Density | 8.65 g/cm³ |
| Melting point | 321.069 °C |
| Boiling point | 767 °C |
Occurrence
Cadmium almost always occurs with zinc in the mineral sphalerite and is recovered as a by-product of zinc refining. It is never mined for itself.
Applications
Nickel-cadmium rechargeable batteries
Yellow, orange, and red pigments
Cadmium telluride solar cells
Corrosion-resistant plating
Common compounds
- Cadmium sulfide
- Cadmium telluride
- Cadmium oxide
Cadmium pigments produce some of the brightest yellows and reds in art — but because cadmium is toxic, safer alternatives are steadily replacing them.
Data source: IUPAC standard atomic weights 2021; NIST physical property data