Cadmium
Symbol: Cd
Atomic Number: 48
Atomic Mass: 112.411 amu (atomic mass units)
Melting Point: 321.07 C (594.22 K, 609.93 F)
Boiling Point: 767.0 C (1040 K, 1413.0 F)
Number of Protons: 48
Number of Electrons: 48
Number of Neutrons: 64
Classification: Transition Metal
Crystal Structure: Hexagonal
Density @ 293 K: 8.69 grams per cubic centimeter
Color: Bluish-white
Cadmium was found as a contaminant in some samples of calamine (zinc carbonate) by the German chemist Friedrich Strohmeyer in 1817. He noted that some of his samples would produce a yellow glow when heated. Further examination of these yellow glowing samples showed them to contain cadmium. Cadmium was named after the Latin and Greek names for calamine – “cadmia” and “kadmeia”.
This bluish white metal is very soft and it is easy to cut cadmium with a knife. A bar of pure cadmium will give out a characteristic “cadmium scream” when bent.
The element and all of its compounds are toxic, with ingestion causing damage to the liver and kidneys. Although it is toxic to humans, there is evidence that cadmium is a necessary element in the nutrition of rats but only in a very, very small quantity.
There are eight naturally occurring isotopes of cadmium, five of which are stable and the other three have extremely long half-lives. The most common of the naturally occurring isotopes is the stable isotope cadmium-114, which makes up 28.73% of the total abundance of the element. Thirty-six other unstable isotopes of cadmium have been identified with half-lives ranging from 0.18 seconds to 14.1 years.
Greenockite is the only mineral ore containing a significant proportion of cadmium. However, greenockite has not been found in any significant quantity anywhere in the world. This makes the production of cadmium from greenockite uneconomical. A small amount of cadmium is present in zinc ores and commercial production of cadmium metal is a by-product of zinc extraction from these ores.
Because of its toxicity, the uses of cadmium and its compounds are limited.
* It can be electroplated on to other metals to prevent corrosion.
* It easily absorbs neutrons and so it is used in control rods for nuclear reactors.
* It is used to make rechargeable nickel-cadmium batteries.
* Alloyed with silver it forms a low melting point solder. Care must be taken when using cadmium based solders to prevent accidental poisoning from fumes.
* Cadmium alloys are used in the production of low friction bearings. Such bearings are highly resistant to metal fatigue.
* Cadmium sulfide forms a yellow pigment used in paints.
* Hydrated cadmium sulfate is used in the Weston cell. This is a battery giving a very precise voltage, which allows its use in the calibrating of laboratory and hospital equipment.
* Cadmium compounds are used as phosphors in black and white as well as color televisions.
Reference sources:
Jefferson Laboratories Science education
Web Elements
Environmental Chemistry.com
