Cadmium

**Cadmium** is a metal. It is element 48 on the periodic table. Its symbol is _Cd_. Its atomic number is 48 and its atomic mass is 112.4. It is found in Group 12 on the periodic table.

### Physical properties

Cadmium is a blue-gray soft metal. It can be considered a transition metal or a post-transition metal. It is malleable and ductile. It is similar to zinc. It melts at 321°C.

Cadmium has 8 natural isotopes. 5 are radioactive, but 3 have very long half-lives so their radioactivity is almost nothing.

### Chemical properties

Cadmium is a moderately reactive metal. It corrodes in moist air and dissolves in acids. It burns in air when powdered to make the brown cadmium oxide.

### Chemical compounds

Cadmium forms chemical compounds in two oxidation states: +1 and +2. The +1 state is rare and unstable. The +2 state is much more common. Most +2 compounds dissolve easily in water and are white to yellow. Cadmium oxide can be brown, red, or white. Cadmium sulfide is bright yellow. Cadmium chloride and cadmium sulfate are colorless solids that dissolve easily in water. Cadmium fluoride is slightly soluble. Cadmium compounds are toxic when inhaled.

- Cadmium bromide, pale yellow solid, dissolves in water
- Cadmium chloride, colorless solid, dissolves in water
- Cadmium fluoride, gray solid, does not dissolve good in water
- Cadmium iodide, pale yellow solid, dissolves in water
- Cadmium oxide, white, brown, or red solid, dissolves in acids
- Cadmium sulfate, colorless solid, dissolves in water
- Cadmium sulfide, bright yellow solid, does not dissolve in water
- Cadmium telluride, black solid, semiconductor

## History

Cadmium was found by two chemists, German chemist Friedrich Stromeyer discovered it in 1817, and Karl Herman also discovered it in 1818. They were looking at an impurity in zinc carbonate and found cadmium. For about 100 years, Germany made most cadmium. Cadmium iodide was used as a medicine although it was toxic.

## Occurrence

Cadmium ores are rare. Greenockite, a cadmium sulfide mineral is the only main ore and it is found with sphalerite, a zinc sulfide. Because of this, most cadmium comes from zinc processing. Cadmium as a metal is very rare but is found in one place in Russia.

## Preparation

China makes the most cadmium. South Korea and Japan also make cadmium. Cadmium is taken from the zinc metal by heating the zinc metal in a vacuum. Cadmium is boiled first. The cadmium is condensed and used. Cadmium is also taken by precipitating it from the solution of zinc sulfate used to make pure zinc by electrolysis.

## Uses

In the 1930s and 1940s cadmium was mainly used to plate steel to prevent it from corroding. Then cadmium sulfide was used as a pigment in paint.

Now, cadmium is mainly used in nickel cadmium batteries. 86% of cadmium is used in batteries as of 2009. Some people are trying to stop using nickel-cadmium batteries because cadmium is toxic. Cadmium is still used to electroplate steel to prevent corrosion. Only about 6% of cadmium is used for this. Cadmium is also used in lasers, nuclear reactors, phosphors, photoresistors, pigments, and semiconductors. Wood's metal, an alloy that melts very easily, has cadmium in it. Cadmium is used in some solder.

Cadmium is not used in the human body or any other animal. A diatom uses cadmium, though.

## Safety

Cadmium is a highly toxic metal. Dust of cadmium or its compounds is very dangerous and can kill. Some countries have banned cadmium from electronics. Cigarette smoking is the most important source of cadmium. Smokers have about 4 times more cadmium in their blood than nonsmokers (people who do not smoke). Cadmium is thought to be carcinogenic, although people still debate whether it is other things with the cadmium that cause cancer, like arsenic.

## Infobox (cadmium)