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 11  Melting point 1064.18°C, 1947.52°F, 1337.33 K 
Period Boiling point 2836°C, 5137°F, 3109 K 
Block Density (g cm−3) 19.3 
Atomic number 79  Relative atomic mass 196.967  
State at 20°C Solid  Key isotopes 197Au 
Electron configuration [Xe] 4f145d106s1  CAS number 7440-57-5 
ChemSpider ID 22421 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
In this image a traditional alchemical symbol for the element is used. It is also used as a sun symbol, and much of the mythology around gold relates to the sun. Early alchemists were obsessed by gold and pursued their desire to transmute base metals (usually lead) into gold. The image in the background is based on a symbolic representation of an alchemist’s ‘laboratory’.
Appearance
A soft metal with a characteristic yellow colour. It is chemically unreactive, although it will dissolve in aqua regia (a mixture of nitric and hydrochloric acids).
Uses
Most mined gold is stored as bullion. It is also, however, used extensively in jewellery, either in its pure form or as an alloy. The term ‘carat’ indicates the amount of gold present in an alloy. 24-carat is pure gold, but it is very soft. 18- and 9-carat gold alloys are commonly used because they are more durable.

The metal is also used for coinage, and has been used as standard for monetary systems in some countries.

Gold can be beaten into very thin sheets (gold leaf) to be used in art, for decoration and as architectural ornament. Electroplating can be used to cover another metal with a very thin layer of gold. This is used in gears for watches, artificial limb joints, cheap jewellery and electrical connectors. It is ideal for protecting electrical copper components because it conducts electricity well and does not corrode (which would break the contact). Thin gold wires are used inside computer chips to produce circuits.

Dentists sometimes use gold alloys in fillings, and a gold compound is used to treat some cases of arthritis.

Gold nanoparticles are increasingly being used as industrial catalysts. Vinyl acetate, which is used to make PVA (for glue, paint and resin), is made using a gold catalyst.
Biological role
Gold has no known biological role, and is non-toxic.
Natural abundance
Gold is one of the few elements to occur in a natural state. It is found in veins and alluvial deposits. About 1500 tonnes of gold are mined each year. About two-thirds of this comes from South Africa and most of the rest from Russia.

Seawater contains about 4 grams of gold in 1,000,000 tonnes of water. Overall this is a huge amount of gold stored in the oceans but, because the concentration is so low, attempts to reclaim this gold have always failed.
 
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) 2.14 Covalent radius (Å) 1.30
Electron affinity (kJ mol−1) 222.749 Electronegativity
(Pauling scale)
2.4
Ionisation energies
(kJ mol−1)
 
1st
890.128
2nd
1949
3rd
-
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 5.7
Crustal abundance (ppm) 0.0013
Recycling rate (%) >30
Substitutability Unknown
Production concentration (%) 13
Reserve distribution (%) 15
Top 3 producers
  • 1) China
  • 2) Australia
  • 3) USA
Top 3 reserve holders
  • 1) Australia
  • 2) South Africa
  • 3) Russia
Political stability of top producer 24.1
Political stability of top reserve holder 74.5
 

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 5,4,3,2, 1,-1
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  197Au 196.967 100
  198Au 197.968 - 2.695 d  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)
129 Young's modulus (GPa) 78.0
Shear modulus (GPa) 27.0 Bulk modulus (GPa) 217.0
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - 3.72
x 10-8
5.44
x 10-5
0.0092 0.374 6.68 67 - -
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History

Gold has been known since prehistoric times and was one of the first metals to be worked, mainly because it was to be found as nuggets or as particles in the beds of streams. Such was the demand that by 2000 BC the Egyptians began mining gold. The death mask of Tutankhamen, who died in 1323 BC, contained 100 kg of the metal. The royal graves of ancient Ur (modern Iraq), which flourished from 3800 to 2000 BC, also contained gold objects.

The minting of gold coins began around 640 BC in the Kingdom of Lydia (situated in what is now modern Turkey) using electrum, a native alloy of gold and silver. The first pure gold coins were minted in the reign of King Croesus, who ruled from 561–547 BC.
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Podcasts

Listen to Gold Podcast
Transcript :

Chemistry in its element: gold


(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, in this week's episode of Chemistry in its element, we're taking a flight on Concorde, dropping by Buckingham Palace and finding out what could form a film just 230 atoms thick. Going for gold for us this week, here's the legendary science broadcaster and populariser Johnny Ball.

Johnny Ball

The element gold. Gold is element 79 and its symbol is Au. Though the name is Anglo Saxon, gold originated from the Latin Aurum, or shining dawn, and previously from the Greek. It's abundance in the earth's crust is 0.004 ppm.

100% of gold found naturally is isotope Au-197. 28 other isotopes can be produced artificially and are all radioactive.

Gold along with silver and copper, form a column in the periodic table. They are found naturally and were the first three elements known to man. They were all used as primitive money well before the first gold coins which appeared in Egypt around 3400 BC.

Most gold is ancient or comes from Central American Aztecs and South American Incas brought to Europe by the Spanish and Portuguese in the 16th century, and which has since been recycled over and over again. In 1830 world output was no more than 12 tonnes per annum. But around that time, new gold discoveries were being made. Finds were discovered in Siberia, California, New South Wales and Victoria, Australia, Transvaal, South Africa, the Klondike and Alaska, and they all produced gold rushes. World production was then around 150 tonnes per year. It is now around 2300 tones per annum.

Because it is found in it's natural state and does not naturally alloy with anything else and because it is the heaviest metal, by sifting rock in water, the gold always falls to the bottom and all less dense impurities are washed away.

The largest nugget was the Welcome Stranger nugget found in Victoria, Australia in 1869. It weighed over 71 kg. This type of nugget occurs naturally, but is very, very rare. Pure gold is 24 karat. 18 karat is 75% and 12 karat is 50% pure gold.

Gold is the most malleable of all metals and soft enough to be cut with a knife. Stone age peoples hammered gold into plates for ornamental purposes. Really quite large amounts were gathered together. Though King Tutankhamun was a minor Pharaoh and died aged 18, his coffin alone contained 112 kg of gold. Egyptians also made thin gold sheets, utensils, vast varieties of jewellery and even gold thread. King Tut when he was buried had over 150 gold ornaments on his body.

Today 1 gram can be beaten into a square metre sheet just 230 atoms thick. 1 cubic centimetre would make a sheet of 18 square metres. Concord's windscreen had a layer of gold to screen pilots from UV light and today it is often used in sky scraper windows to cut down both heat and UV from sunlight. 1 gram can be drawn to make 165 metres of wire 20 um (microns) thick (1/200th of a millimeter)

The gold colour in the Buckingham Palace fence is actually gold covered, as it lasts 30 years, whereas gold paint (which contains no gold at all) lasts in tip top condition, only about a year.

Sea water contains around 3 parts in a billion of gold, but there's never been found an economic means of recovering it. The Germans tried very hard during the second World War but failed miserably.

The largest modern hoard is the 30,000 tons in the US Federal Reserve Bank in New York, which belongs to 18 different nations. It is estimated that all the world's gold gathered together would only make a cube around 18 metres per side - about 6000 cubic metres. And that's gold.

Chris Smith

So now you know why pirates used to bite gold coins to see if they were real. It wasn't just for the camera because it looked good, it was because the metal was soft enough to be marked by teeth. That was Johnny Ball telling the story of gold. Next time on Chemistry in its element Victoria Gill introduces the chemical that founded the science of photography and also helped to launch the careers of successions of Oscar winners.

Victoria Gill

in 1840, Henry Talbot discovered an additional chemical twist, that a so called latent silver image, that had been briefly exposed onto a layer of silver iodide could be revealed using gallic acid. The effect was seen as magical, a devilish art. Hollywood could never have existed without the chemical reaction that gave celluloid film its ability to capture the stars and bring them to the aptly dubbed silver screen.

Chris Smith

And you can hear Victoria Gill crossing your cognitive palm and lining your intellectual pocket with silver on next week's Chemistry in its element. I'm Chris Smith, thank you for listening, see you next time.

(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

Description :
Discover the chemistry and history behind the Gold, Silver and Bronze Olympic medals.
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Gold is the most malleable and ductile of all metals. It can be hammered to a few hundred atoms thick and we don't have to panic too much about wasting small quantities when demonstrating some of its...
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Assessment for Learning is an effective way of actively involving students in their learning. This is a series of plans based around chemistry topics.
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When concentrated hydrochloric acid is added to a very dilute solution of copper sulfate, the pale blue solution slowly turns yellow-green on the formation of a copper chloride complex. When concentr...
 

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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.

 

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