Periodic Table > Germanium
 

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 14  Melting point 938.25°C, 1720.85°F, 1211.4 K 
Period Boiling point 2833°C, 5131°F, 3106 K 
Block Density (g cm−3) 5.3234 
Atomic number 32  Relative atomic mass 72.630  
State at 20°C Solid  Key isotopes 73Ge, 74Ge 
Electron configuration [Ar] 3d104s24p2  CAS number 7440-56-4 
ChemSpider ID 4885606 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
Germanium was used in early transistors similar to the one featured here.
Appearance
A silvery-white semi-metal. It is brittle.
Uses
Germanium is a semiconductor. The pure element was commonly doped with arsenic, gallium or other elements and used as a transistor in thousands of electronic applications. Today, however, other semiconductors have replaced it.

Germanium oxide has a high index of refraction and dispersion. This makes it suitable for use in wide-angle camera lenses and objective lenses for microscopes. This is now the major use for this element.

Germanium is also used as an alloying agent (adding 1% germanium to silver stops it from tarnishing), in fluorescent lamps and as a catalyst.

Both germanium and germanium oxide are transparent to infrared radiation and so are used in infrared spectroscopes.
Biological role
Germanium has no known biological role. The element is non-toxic. Certain germanium compounds have low toxicity in mammals, while being effective against some bacteria. This has led some scientists to study their potential use in pharmaceuticals.
Natural abundance
Germanium ores are very rare. They are found in small quantities as the minerals germanite and argyrodite.

Germanium minerals are also present in zinc ores, and commercial production of germanium is carried out by processing zinc smelter flue dust. It can also be recovered from the by-products of combustion of certain coals.
 
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) 2.11 Covalent radius (Å) 1.20
Electron affinity (kJ mol−1) 118.939 Electronegativity
(Pauling scale)
2.01
Ionisation energies
(kJ mol−1)
 
1st
762.179
2nd
1537.456
3rd
3302.124
4th
4410.644
5th
9021.4
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 8.1
Crustal abundance (ppm) 1.3
Recycling rate (%) <10
Substitutability Medium
Production concentration (%) 67
Reserve distribution (%) Unknown
Top 3 producers
  • 1) China
  • 2) Russia
  • 3) Germany (likely)
Top 3 reserve holders
  • Unknown
Political stability of top producer 24.1
Political stability of top reserve holder Unknown
 

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 4
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  70Ge 69.924 20.57
  72Ge 71.922 27.45
  73Ge 72.923 7.75 > 1.8 x 1023 β- 
  74Ge 73.921 36.5
  76Ge 75.921 7.73 1.6 X 1021 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)
320 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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History

Germanium was discovered by Clemens A. Winkler at Freiberg, Germany, in 1886. Its existence had been predicted by Mendeleev who predicted its atomic weight would be about 71 and that its density around 5.5 g/cm3.

In September 1885 a miner working in the Himmelsfürst silver mine near Freiberg, came across an unusual ore. It was passed to Albin Weisbach at the nearby Mining Academy who certified it was a new mineral, and asked his colleague Winkler to analyse it. He found its composition to be 75% silver, 18% sulfur, and 7% he could not explain. By February 1886, he realised it was a new metal-like element and as its properties were revealed, it became clear that it was the missing element below silicon as Mendeleev had predicted. The mineral from which it came we know as argyrodite, Ag8GeS6.
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Podcasts

Listen to Germanium Podcast
Transcript :

Chemistry in its element: germanium


(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

This week, flowers, fibre optics and the element that can't quite make up its mind whether it's a metal or not. Taking us back to school, here's Brian Clegg.

Brian Clegg

If there were a competition for the chemical element mostly likely to generate schoolboy howlers, the winner should be germanium. It's inevitable that the substance with atomic number 32 is quite often described as a flowering plant with the common name cranesbill. Just one letter differentiates the flower geranium from the element germanium - an easy enough mistake.

We know germanium isn't a flower, but it's slightly harder to say just what it is. Most elements are either metals or nonmetals. Germanium falls in the same group as carbon and silicon, but also as tin and lead. Germanium itself is classified as a metalloid. It's hard at room temperature and looks metallic with a shiny silvery grey finish, but it's a semiconductor, without some of the key properties of a metal.

Germanium's existence was predicted before anyone isolated it. This was a triumph for Dmitri Mendeleev in his construction of the periodic table. By 1869, Mendeleev had assembled a crude table of the known elements, arranging them according to their chemical properties and atomic weights. But his table had a number of prominent gaps. Mendeleev predicted that these represented unknown elements. He named them using the substance in the table sitting above the gap with the prefix eka, which is Sanskrit for the number 'one'. So, Mendeleev said, we should also have ekaboron, eka-aluminium, ekamanganese and ekasilicon.

Of these, by far the most accurate prediction was for ekasilicon, occupying the slot we now give to germanium. Mendeleev came up with an atomic weight of 72, compared to an actual value of 72.6 from its four stable isotopes 70, 72 73 and 74. He was also pretty well spot on with its density and in predicting that it would have a high melting point - he even said it would be gray in colour.

It was seventeen years later, in 1886, that German chemist Clemens Winkler isolated the element from a newly discovered mineral called argyrodite, found in a mine near his home town of Freiburg in Saxony. Winkler first toyed with the name neptunium, after the recently discovered planet. But in 1877, a fellow chemist called Hermann had found a substance in the mineral tantalite which he believed was a new metallic element. Hermann had already taken the name neptunium for what later proved to be a mistaken finding. There was no new element in the tantalite.

Unaware of this mistake, Winkler decided to name his new element after his country. At the time, Germany was still relatively new, unified in the Franco-Prussian war in 1871. It might seem strange that he called his find germanium when Winkler knew his country as Deutschland, but the tradition was to use Latin names where possible, and the Romans had known much of the area as Germania, so this is where the element truly took its name from.

For a good fifty years, germanium was little more than a box on the periodic table. It really wasn't good for anything. It was only with the development of electronics that germanium's value as a very effective semiconductor came to light. A semiconductor is a material with conductivity between a conductor and an insulator, whose conductivity can be altered by an outside influence like an electric field or the impact of light.

The first use of germanium on a large scale was to replace the most basic electronic component, the diode. In the original valve or vacuum tube form, this had a heater that gave off electrons and an anode to which the electrons were attracted across a vacuum. It's like a one way flow valve in a water pipe - electrons can flow from the heater to the anode, but not the other way round.

As a semiconductor, germanium allowed the production of a solid state equivalent to the diode. Like most semiconductors, germanium can have impurities added to make it an electron donor - a so-called n-type material - or an electron acceptor, called p-type. By marrying p and n type strips of germanium, the element provided the same diode effect.

Germanium really took off with the development of the transistor, a solid state version of the triode valve. Here a small current can be used to control a larger one, amplifying a signal or acting as a switch. Germanium transistors were very common, but now have been replaced by silicon.

This is partly a matter of availability - as silicon in the primary constituent of sand, there's plenty out there, where germanium has to be mined at considerable expense. And silicon is a more effective semiconductor for making electronic components. But to have the effective silicon electronics we now depend on for everything from computers to mobile phones, requires extreme precision in purifying the element, which meant that silicon electronics weren't feasible on a large scale until the 1970s.

Once silicon took over, it might seem that germanium would be relegated to the backwaters of chemical obscurity as an also-ran that was no longer worth using. This has not happened because there are still applications where germanium is valuable, particularly in the specialist electronics of night vision equipment and as a component with silica in the fibre of the fibre optic cables used in communications.

Unlike many of the basic elements, there aren't many germanium compounds that have found a use. Germanium dioxide can be used as a catalyst in the production of the PET plastic used in many bottles, though it is rarely employed for this in Europe and the US. It is still primarily the pure element that has a role, if rather more specialized than it first was, in our electronics and communications. You may like to say it with flowers and give someone a gift of a geranium - but you're more likely to communicate down a modern fibre optic phone line, and then its germanium all the way.

Chris Smith

Brian Clegg with the story of germanium, which was named after the country it first came from. And speaking of elements named after countries, here's another one, although you'll have to look very hard to find it.

Peter Wothers

Whilst it is naturally occurring, or to be more precise, naturally formed - albeit briefly - during radioactive decay of other elements, the amount of francium on earth is tiny. It has been estimated that at any one time there is less than a kilogram of the element in the entire earth's crust.

Chris Smith

And bizarrely, despite being at the bottom of group one of the Periodic Table, Francium isn't actually as reactive as Cesium. And we'll hear why with Peter Wothers 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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This project is creating a collection of unique human stories by award-winning filmmakers about the endless ways the elements touch our daily lives.
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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.