Periodic Table > Silicon
 

Terminology


Allotropes
Some elements exist in several different structural forms, these are called allotropes.


For more information on Murray Robertson’s image see Uses/Interesting Facts below.

 

Fact Box Terminology


Group
Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.


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, principal, diffuse, and fundamental.


Atomic Number
The number of protons in the nucleus.


Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.


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


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.


Melting Point (oC)
The temperature at which the solid-liquid phase change occurs.


Melting Point (K)
The temperature at which the solid-liquid phase change occurs.


Melting Point (oF)
The temperature at which the solid-liquid phase change occurs.


Boiling Point (oC)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (oF)
The temperature at which the liquid-gas phase change occurs.


Sublimation
Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.


Density (kgm-3)
Density is the weight of a substance that would fill 1 m3 (at 298 K unless otherwise stated).


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.


Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. 12C has 6 protons and 6 neutrons and 13C has 6 protons and 7 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 (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact Box

 
Group 14  Melting point 1414 oC, 2577.2 oF, 1687.15 K 
Period Boiling point 3265 oC, 5909 oF, 3538.15 K 
Block Density (kg m-3) 2329 
Atomic number 14  Relative atomic mass 28.086  
State at room temperature Solid  Key isotopes 28Si, 30Si 
Electron configuration [Ne] 3s23p2  CAS number 7440-21-3 
ChemSpider ID 4574465 ChemSpider is a free chemical structure database
 

Interesting Facts terminology


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.


Natural Abundance

Where this element is most commonly found in nature.


Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.


Appearance

The description of the element in its natural form.

Uses / Interesting Facts

 
Image explanation

An image based on a Diatom, an ancient type of phytoplankton, unique in that their cell walls are siliceous.

Appearance

The element itself, when ultrapure, is blue-grey and used as the semiconductor in ‘silicon chips’.

Source

Uses

Silicon is one of the most useful elements to mankind. It is used extensively, as the element, in solid-state devices in the computer and microelectronics industries. For this, hyperpure silicon is needed, prepared by thermal decomposition of ultra-pure trichlorosilane, followed by recrystalisation. The silicon is then selectively doped with tiny controlled amounts of boron, gallium, phosphorus or arsenic. Every year, 80,000 tonnes of semiconductor-grade silicon and 8 million tonnes of ferro-silicon (including some metallurgy-grade silicon) are produced for the steel and metallurgical industries. Granite and most other rocks are complex silicates which we use for civil engineering projects. Sand (silicon dioxide or silica) and clay (aluminium silicate) are used to make concrete and cement. Sand is also the principal ingredient of glass, which has thousands of uses. Silicon carbides are important abrasives and also used in lasers. Silicon, as silicate, is present in pottery, enamels, and in high-temperature ceramics.

Biological role

Silicon is essential to plant life but its use in animal cells is uncertain. Phytoliths are tiny particles of silica that form within some plants. Since they do not rot they provide us with useful evolutionary fossil evidence. Silicon is non-toxic but some silicates, such as asbestos, are carcinogenic. Some workers such as miners and stonecutters who are exposed to siliceous dust often develop a serious lung disease called silicosis.

Natural abundance

Silicon makes up 25.7% of the Earth’s crust by mass and is the second most abundant element (oxygen is the first). It does not occur uncombined in nature but occurs chiefly as the oxide (silica) and as silicates. The oxide includes sand, quartz, rock crystal, amethyst, agate, flint and opal. The silicate form includes asbestos, granite hornblende, feldspar, clay and mica.

 
Atomic Data Terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron affinity (kJ mol-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *


Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, Ed in eV. χA - χB =(eV)-1/2sqrt(Ed(AB)-[Ed(AA)+Ed(BB)]/2), with χH set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).


1st Ionisation energy (kJ mol-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).


Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic Data

 
Atomic radius, non-bonded (Å) 2.100 Covalent radius (Å) 1.14
Electron affinity (kJ mol-1) 134.115 Electronegativity
(Pauling scale)
1.900
Ionisation energies
(kJ mol-1)
 
1st
786.518
2nd
1577.133
3rd
3231.583
4th
4355.519
5th
16090.557
6th
19805.529
7th
23783.616
8th
29287.135
 
Bonding and Enthalpies terminology

Covalent Bonds
The strengths of several common covalent bonds.

Bonding / Enthalpies

 
Covalent bonds
Si–Si  226  kJ mol -1 O–Si  466  kJ mol -1 O=Si  638  kJ mol -1
O≡Si  805  kJ mol -1 C–Si  307  kJ mol -1 H–Si  318  kJ mol -1
H–Si  364  kJ mol -1  
 

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.


Key for numbers generated


Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9


Reserve base distribution

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)


Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %


Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)


Explanations for terminology


Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.


Sourced

The country with the largest reserve base.


Reserve Base Distribution

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.


Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.


Total Governance Factor

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.


Relative Supply Risk Index

The Crustal Abundance, Reserve Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply Risk

 
Scarcity factor Unknown
Country with largest reserve base Unknown
Crustal abundance (ppm) Unknown
Leading producer Unknown
Reserve base distribution (%) Unknown
Production concentration (%) Unknown
Total governance factor(production) Unknown
Top 3 countries (mined)
  • Unknown
Top 3 countries (production)
  • Unknown
 

Oxidation states/ Isotopes


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

Terminology


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. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.


Important Oxidation states
The most common oxidation states of an element in its compounds.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Oxidation States / Isotopes

 
Common oxidation states 4, -4
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  28Si 27.977 92.223
  29Si 28.976 4.685
  30Si 29.974 3.092
 

Pressure and Temperature - Advanced Terminology


Molar Heat Capacity (J mol-1 K-1)

Molar heat capacity is the energy required to heat a mole of a substance by 1 K.


Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, 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 (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.


Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour Pressure (Pa)

Vapour pressure is the 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 / Temperature - Advanced

 
Molar heat capacity
(J mol-1 K-1)
19.99 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 100
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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History

Silica (SiO2) in the form of sharp flints were among the first tools made by humans. The ancient civilizations used other forms of silica such as rock crystal, and knew how to turn sand into glass. Considering silicon’s abundance, it is somewhat surprising that it aroused little curiosity among early chemists.


Attempts to reduce silica to its components by electrolysis had failed. In 1811, Joseph Gay Lussac and Louis Jacques Thénard reacted silicon tetrachloride with potassium metal and produced some very impure form of silicon. The credit for discovering silicon really goes to the Swedish chemist Jöns Jacob Berzelius of Stockholm who, in 1824, obtained silicon by heating potassium fluorosilicate with potassium. The product was contaminated with potassium silicide, but he removed this by stirring it with water, with which it reacts, and thereby obtained relatively pure silicon powder.

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Podcasts

Listen to Silicon Podcast
Transcript :

Chemistry in its element - silicon


(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) 

Meera Senthilingam 

For this week's element we enter the world of science fiction to explore life in outer space. Here's Andrea Sella. 

Andrea Sella 

When I was about 12, my friends and I went through a phase of reading science fiction. There the were the fantastic worlds of Isaac Asimov, Larry Niven and Robert Heinlein, involving impossible adventures on mysterious planets - the successes of the Apollo space programme at the time only helped us suspend our disbelief. One of the themes I remember from these stories was the idea that alien life forms, often based around the element silicon, abounded elsewhere in the universe. Why silicon? Well, it is often said that elements close to each other in the periodic table share similar properties and so, seduced by the age-old red herring that "carbon is the element of life", the writers selected the element below it, silicon. 

I was reminded of these readings a couple of weeks ago when I went to see an exhibition of work by a couple of friends of mine. Called "Stone Hole" it consisted of stunning panoramic photographs taken at extremely high resolution inside sea caves in Cornwall. As we wandered through the gallery a thought occurred to me. "Could one imagine a world without silicon?" Every single photograph was, not surprisingly, dominated by rocks based on silicon and it was a powerful reminder of the fact that silicon is the second most abundant element in the earth's crust, beaten to first place by oxygen, the element with which it invariable entangled. 

Silicate rocks - those in which silicon is surrounded tetrahedrally by four oxygen atoms - exist in an astonishing variety, the differences being determined by how the tetrahedra building blocks link together, and what other elements are present to complete the picture. When the tetrahedra link one to the next, one gets a mad tangle of chains looking like an enormous pot of spaghetti - the sorts of structures one gets in ordinary glass. 

The purest of these chain-like materials is silicon dioxide - silica - found quite commonly in nature as the colourless mineral quartz or rock crystal. In good, crystalline quartz, the chains are arranged in beautiful helices and these can all spiral to the left. Or to the right. When this happens the crystals that result are exact mirror images of each other. But not superimposable - like left and right shoes. To a chemist, these crystals are chiral, a property once thought to be the exclusive property of the element carbon, and chirality, in turn, was imagined to be a fundamental feature of life itself. Yet here it is, in the cold, inorganic world of silicon. 

Most grandiose of all, one can make porous 3D structures - a bit like molecular honeycombs - particularly in the presence of other tetrahedral linkers based on aluminium. These spectacular materials are called the zeolites, or molecular sieves. By carefully tailoring the synthetic conditions, one can build material in which the pores and cavities have well defined sizes - now you have a material that can be used like a lobster traps, to catch molecules or ions of appropriate size. 

But what of the element itself? Freeing it from oxygen is tough, it hangs on like grim death and requires brutal conditions. It was Humphrey Davy, the Cornish chemist and showman, who first began to suspect that silica must be a compound, not an element. He applied electric currents to molten alkalis and salts and to his astonishment and delight, isolated some spectacularly reactive metals, including potassium. He now moved on to see what potassium could do. Passing potassium vapour over some silica he obtained a dark material that he could then burn and convert back to pure silica. Where he pushed, others followed. In France, Thénard and Gay-Lussac carried out similar experiments using silicon fluoride. Within a couple of years, the great Swedish analyst Jöns Jakob Berzelius had isolated a more substantial amount of the material and declared it an element. 

Silicon's properties are neither fish nor fowl. Dark gray in colour and with a very glossy glass-like sheen, it looks like a metal but is in fact quite a poor conductor of electricity, and there in many ways, lies the secret of its ultimate success. The problem is that electrons are trapped, a bit like pieces on a draughts board in which no spaces are free. What makes silicon, and other semiconductors, special is that it is possible to promote one of the electrons to an empty board - the conduction band - where they can move freely. It's a bit like the 3-dimensional chess played by the point-eared Dr Spock in Star Trek. Temperature is crucial. Warming a semiconductor, allow some electrons to leap, like salmon, up to the empty conduction band. And at the same time, the space left behind - known as a hole - can move too. 

But there is another way to make silicon conduct electricity: it seems perverse, but by deliberately introducing impurities like boron or phosphorus one can subtly change the electrical behaviour of silicon. Such tricks lie at the heart of the functioning of the silicon chips that allow you to listen to this podcast. In less than 50 years silicon has gone from being an intriguing curiosity to being one of the fundamental elements in our lives. 

But the question remains, is silicon's importance simply restricted to the mineral world? The prospects do not seem good - silicate fibres, like those in blue asbestos are just the right size to penetrate deep inside the lungs where they pierce and slash the inner lining of the lungs. And yet, because of its extraordinary structural variability, silicon chemistry has been harnessed by biological systems. Silicate shards lurk in the spines of nettles waiting to score the soft skin of the unwary hiker and inject minuscule amounts of irritant. And in almost unimaginable numbers delicate silicate structures are grown by the many tiny life-forms that lie at the base of marine food chains, the diatoms. 

Could one therefore find silicon-based aliens somewhere in space? My hunch would probably be not. Certainly not as the element. It is far too reactive and one will always find it associated with oxygen. But even linked with oxygen, it seems unlikely, or at least not under the kinds of mild conditions that we find on earth. But then again, there is nothing like a surprise to make one think. As the geneticist J B S Haldane put it, "The universe is not queerer than we suppose. It is queerer than we can suppose". I live in hope. 

Meera Senthilingam 

So although unlikely there could be some silicon based surprises lurking out in space. That was the ever hopeful Andrea Sella from University College London with the life forming chemistry of silicon. Now next week we hear about Roentgenium the element that we need to get just right. 

Simon Cotton 

The idea was to make the nickel ions penetrate the bismuth nucleus, so that the two nuclei would fuse together, making a bigger atom. The energy of the collision had to be carefully controlled, because if the nickel ions were not going fast enough, they could not overcome the repulsion between the two positive nuclei and would just fly off the bismuth on contact. However, if the nickel ions had too much energy, the resulting "compound nucleus" would have so much excess energy that it could just undergo fission and fall apart. The trick was, like Goldilocks' porridge, to be "just right", so that the fusion of the nuclei would occur, just. Meera Senthilingam And join Simon Cotton to find out how successful collisions were created by the founders of the element Roentgenium in next week's Chemistry in its Element. Untill then I'm Meera Senthilingam and thank you for listening. 

(Promo) 

Chemistry in its element is 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. 

(End promo) 

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  Help Text

Resources

Description :
The reactions of group IV elements
Description :
The silanes are generally more reactive than their hydrocarbon analogues, and ignite spontaneously on contact with air. They also react explosively with F2, Cl2 and Br2.
Description :
Magnesium and sand are heated together and silicon is produced by an exothermic reaction. The product is placed in acid to remove magnesium oxide and unreacted magnesium. Small amounts of silanes are...
Description :
This experiment illustrates a reaction with low activation energy. Magnesium reacts with silicon to produce magnesium silicide. This then decomposes in dilute acid to produce silane, which spontaneou...
Description :
Use your scientific knowledge and skills to find out what you can about the properties of an unknown element
Description :
The formation of molten silicates in the Earth’s mantle involves the formation of silicon dioxide and its subsequent reaction at high temperatures with metal oxides. In this experiment coloured silic...
 

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References

 
Images:  Visual Elements © Murray Robertson 2011
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.