Periodic Table > Cadmium
 

Glossary


Allotropes
Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.


For more information on the Visual Elements image see the Uses and properties section below.

 

Glossary


Group
A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.


Block
Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).


Atomic number
The number of protons in an atom.


Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.


Melting point
The temperature at which the solid–liquid phase change occurs.


Boiling point
The temperature at which the liquid–gas phase change occurs.


Sublimation
The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.


Density (g cm−3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.


Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.


Isotopes
Atoms of the same element with different numbers of neutrons.


CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.


Fact box

 
Group 12  Melting point 321.069°C, 609.924°F, 594.219 K 
Period Boiling point 767°C, 1413°F, 1040 K 
Block 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
 

Glossary


Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


Appearance

The description of the element in its natural form.


Biological role

The role of the element in humans, animals and plants.


Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

 
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.
 
Glossary

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.


Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.


Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.


Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.


First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

 
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
-
 

Glossary

Data for this section been provided by the British Geological Survey.


Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.


Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.


Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


Substitutability

The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact


Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.


Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.


Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.


Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.


Supply risk

 
Relative supply risk 6.7
Crustal abundance (ppm) 0.08
Recycling rate (%) 10–30
Substitutability Low
Production concentration (%) 32
Reserve distribution (%) 20
Top 3 producers
  • 1) China
  • 2) Republic of Korea
  • 3) Japan
Top 3 reserve holders
  • 1) India
  • 2) China
  • 3) Australia
Political stability of top producer 24.1
Political stability of top reserve holder 10.8
 

Glossary


Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Isotopes

Atoms of the same element with different numbers of neutrons.


Key for isotopes


Half life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Oxidation states and isotopes

 
Common oxidation states 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  106Cd 105.906 1.25 > 1.9 x 1019 EC, EC 
  108Cd 107.904 0.89 > 4.1 x 1017 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 β-β- 
  114Cd 113.903 28.73 > 1.3 x 1018 β-β- 
  116Cd 115.905 7.49 3.8 x 1019 β-β- 
 

Glossary


Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.


Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.


Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.


Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

 
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)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
0.00028 18.2 - - - - - - - - -
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History

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.
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Podcasts

Listen to Cadmium Podcast
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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Resources

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In this experiment you will be looking at a group of transition elements chromium, molybdenum and tungsten.
Description :
The purpose of this experiment is to examine some of the solution chemistry of the transition elements.
 

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References

 
Visual Elements images and videos
© Murray Robertson 2011.

 

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 3.0), 2010, National Institute of Standards and Technology, Gaithersburg, MD, accessed December 2014.
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

© John Emsley 2012.

 

Podcasts

Produced by The Naked Scientists.

 

Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.