| Discovery date | 1817 |
| Discovered by | Friedrich Stromeyer |
| Origin of the name | The name is derived from the Latin 'cadmia', the name for the mineral calamine. |
| Allotropes | - |
Cd
Cadmium
48
112.414
| Group | 12 | Melting point | 321.069°C, 609.924°F, 594.219 K |
| Period | 5 | Boiling point | 767°C, 1413°F, 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 | |
Image explanation
Cadmium is naturally occurring in the Earth’s crust. The image includes an alchemical symbol once used to represent ‘earth’ elements, against a background projection of the Earth.
Appearance
Cadmium is a silvery metal with a bluish tinge to its surface.
Uses
Cadmium is a poison and is known to cause birth defects and cancer. As a result, there are moves to limit its use.
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.
Biological role
Cadmium is toxic, carcinogenic and teratogenic (disturbs the development of an embryo or foetus). On average we take in as little as 0.05 milligrams per day. But it accumulates in the body, and so on average we store about 50 milligrams.
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.
Natural abundance
The only mineral containing significant quantities of cadmium is greenockite (cadmium sulfide). It is also present in small amounts in sphalerite. Almost all commercially produced cadmium is obtained as a by-product of zinc refining.
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.
| Atomic radius, non-bonded (Å) | 2.18 | Covalent radius (Å) | 1.40 |
| Electron affinity (kJ mol−1) | Not stable |
Electronegativity (Pauling scale) |
1.69 |
|
Ionisation energies (kJ mol−1) |
1st
867.772
2nd
1631.404
3rd
3616.27
4th
-
5th
-
6th
-
7th
-
8th
-
|
||
| 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 | |
| 110Cd | 109.903 | 12.49 | - | - | |
| 111Cd | 110.904 | 12.8 | - | - | |
| 112Cd | 111.903 | 24.13 | - | - | |
| 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- | |
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Specific heat capacity (J kg−1 K−1) |
231 | Young's modulus (GPa) | 49.9 | |||||||||||
| Shear modulus (GPa) | 19.2 | Bulk modulus (GPa) | 41.6 | |||||||||||
| Vapour pressure | ||||||||||||||
| Temperature (K) |
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| Pressure (Pa) |
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| Listen to Cadmium Podcast |
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Transcript :
Chemistry in its element: cadmium (Promo) You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry. (End promo) Chris Smith Hello, this week we're learning a very painful lesson about a heavy metal Steve Mylon 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. So, how do our bodies do it? We take advantage of cadmium chemistry. The cadmium ion is positively charged and posses a large polarizability. Think of it like a water balloon with many electrons sloshing around from side to side. To a chemist, this is referred to as "soft (or B-type) lewis acid' behavior. These soft lewis acids prefer the company of soft lewis bases such as negatively charged (reduced) sulfur - aka sulfide. As cadmium gets absorbed by the human body it stimulates the production of the enzyme metallothionein which has an abundance of sulfide containing amino acids. Each metallothionein enzyme can sequester up to seven cadmium ions providing a fairly nice buffer against high cadmium intake. Those people who suffered from the ouch ouch disease just had too much cadmium in their diets which overwhelmed the sophisticated and elegant defense mechanism. 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. Chris Smith 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. Katherine Holt 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? Chris Smith 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. (Promo) Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements. (End promo)
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Visual Elements images and videos
© Murray Robertson 1998-2017.
W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.
John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.
Derived in part from material provided by the British Geological Survey © NERC.
Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.
Produced by The Naked Scientists.
Created by video journalist Brady Haran working with chemists at The University of Nottingham.
© Murray Robertson 1998-2017.
Data
W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.
Uses and properties
John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.
Supply risk data
Derived in part from material provided by the British Geological Survey © NERC.
History text
Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.
Podcasts
Produced by The Naked Scientists.
Periodic Table of Videos
Created by video journalist Brady Haran working with chemists at The University of Nottingham.
