|Group||12||Melting point||321.069 oC, 609.924 oF, 594.219 K|
|Period||5||Boiling point||767 oC, 1413 oF, 1040 K|
|Block||d||Density (g cm-3)||8.69|
|Atomic number||48||Relative atomic mass||112.414|
|State at 20°C||Solid||Key isotopes||114Cd|
|Electron configuration||[Kr] 4d105s2||CAS number||7440-43-9|
|ChemSpider ID||22410||ChemSpider is a free chemical structure database|
80% of cadmium currently produced is used in rechargeable nickel-cadmium batteries. However, they are gradually being phased out and replaced with nickel metal hydride batteries.
Cadmium was often used to electroplate steel and protect it from corrosion. It is still used today to protect critical components of aeroplanes and oil platforms.
Other past uses of cadmium included phosphors in cathode ray tube colour TV sets, and yellow, orange and red pigments.
Cadmium absorbs neutrons and so is used in rods in nuclear reactors to control atomic fission.
Before the dangers of cadmium were fully understood, welders and other metal workers were at risk of becoming ill. In 1966 some welders working on the Severn Road Bridge became ill from breathing in cadmium fumes.
|Common oxidation states||2|
|Isotopes||Isotope||Atomic mass||Natural abundance (%)||Half life||Mode of decay|
|106Cd||105.906||1.25||> 1.9 x 1019 y||EC, EC|
|108Cd||107.904||0.89||> 4.1 x 1017 y||EC EC|
|113Cd||112.904||12.22||8.04 x 1015 y||β-β-|
|114Cd||113.903||28.73||> 1.3 x 1018 y||β-β-|
|116Cd||115.905||7.49||3.8 x 1019 y||β-β-|
In the early 1800s, the apothecaries of Hanover, Germany, made zinc oxide by heating a naturally occurring form of zinc carbonate called cadmia. Sometimes the product was discoloured instead of being pure white, and when Friedrich Stromeyer of Göttingen University looked into the problem he traced the discoloration to a component he could not identify, and which he deduced must be an unknown element. This he separated as its brown oxide and, by heating it with lampblack (carbon), he produced a sample of a blue-grey metal which he named cadmium after the name for the mineral. That was in 1817. Meanwhile two other Germans, Karl Meissner in Halle, and Karl Karsten in Berlin, were working on the same problem and announced their discovery of cadmium the following year.
|Listen to Cadmium Podcast|
Chemistry in Its Element - Cadmium
You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry
Hello, this week we're learning a very painful lesson about a heavy metal
Ouch Ouch !
I cannot imagine that this is all someone would be saying if they were unfortunate enough to be stricken with the disease of the same name. That's right, the ouch-ouch disease.
From the description, it seems like the pain would be intense enough to make me say a lot more than just ouch-ouch.
Itai-Itai is the original Japanese for ouch ouch. The disease results from excessive cadmium poisoning and was first reported in a small town about 200 miles north west of Tokyo. There, rice grown in cadmium contaminated soils had more than 10 times the cadmium content than normal rice. Excess cadmium began to interfere with calcium deposition in bones. The ouch-ouch-ness of this disease resulted from weak and brittle bones subject to collapse due to high porosity.
It is amazing to think that cadmium was able to accumulate to such high levels that it could overwhelm the human body's already intense defenses against it. It's an insidious little, I mean, heavy metal.
Cadmium sits right below zinc on the periodic table and therefore shares many of its same chemical properties. In the environment it is distributed nearly everywhere we find Zinc and therefore when we mine zinc, we consequently mine cadmium. When we galvanize (zinc treat) a nail or some other bit of steel, a little cadmium comes along for the ride.
Think for a minute about how important galvanization is to the industrialized world. If you don't know, trust me, it's really important, and as such, this little bit of cadmium that comes along for the ride, becomes a lot of potential cadmium exposure. Add that to other avenues of exposure, like mines and metal processing along with the ease of cadmium uptake by agricultural crops, and we really are lucky our bodies have developed a system to attenuate the cadmium exposure in our diets. If not, a lot more of us might be saying Ouch ouch.
I certainly don't want to give you the idea that cadmium has a completely chequered past. One of the things that makes cadmium so interesting is its many useful properties as well.
To give cadmium its fair shake, you should know some of the most brilliant colours and paints result from cadmium salts and artists have taken advantage of these for years.
Nickel-cadmium batteries show promise through higher efficiencies which will demonstrate their importance in the next generation of electric vehicles.
Cadmium is an essential element in many forms of a new class of semi-conductor known as quantum dots. These advanced materials show promise in the areas of electronics, photo-voltaics and medical imaging. And finally in nature, a group at Princeton University a few years back showed that some marine diatons can substitute cadmium for zinc in the important enzyme carbonic anhydrase. This demonstrated that cadmium can be a nutrient as well. For we humans however, don't count on any nutritive value in cadmium, leave that to the dietons. Cadmium intake through contaminated foods or even tobacco smoking can lead to all kinds of problems, some even worse than the ouch-ouch disease.
So the take home message is, don't eat your rechargeables. That was Steve Mylon with the story of Cadmium, the chemical that keeps the world looking a nice range of colours. Next week, from colouring the world to changing it.
Tin cans, tin foil, tin whistles, tin soldiers.....these are that things that come to mind when we think of tin. Which is unfortunate, as tin cans are actually made from steel; tin foil is made from aluminium and tin whistles....well you get the idea. To be associated with a list of obsolete consumable items is especially unfortunate for tin, when we consider that it was responsible for literally changing civilisation! Have you heard of the Bronze Age?
Well if not, do join Katherine Holt to find out how Tin made it all happen on next week's Chemistry in its Element. I'm Chris Smith, thank you for listening and goodbye.
Chemistry in its elementis brought to you by the Royal Society of Chemistry and produced by thenakedscientists dot com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld dot org forward slash elements.
Mining and Sourcing data: British Geological Survey – natural environment research council.
Text: John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.