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.

Silicon

Discovery date	1824
Discovered by	J.J. Berzelius
Origin of the name	The name is derived from the Latin 'silex' or 'silicis', meaning flint.
Allotropes	amorphous Si, crystalline Si

28.086

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	3	Boiling point	3265 ^oC, 5909 ^oF, 3538.15 K
Block	p	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 second most abundant element on the surface of the Earth after oxygen. Sand and flint are silicon dioxide, as are semi-precious stones such as rock crystal and rhinestone. The element itself, when ultrapure, is blue-grey and used as the semiconductor in ‘silicon chips’. Every year, 5,000 tonnes of semiconductor-grade silicon and 500,000 tonnes of metallurgy-grade silicon are produced. Silicon is essential for some species, and perhaps for humans, in whom it is found in connective tissue and skin.

Uses

Silicon is one of the most useful elements to mankind. Sand and clay, which both contain silicon, are used to make concrete and cement. Sand is also the principal ingredient of glass, which has thousands of uses. Silicon is a component of steel, and silicon carbides are important abrasives and also used in lasers. Silicon is present in pottery and enamels, and in high-temperature materials. However, silicon is increasingly used in micro-electronic devices. The silicon is usually doped with precise, very small amounts of boron, gallium, phosphorus or arsenic for use in transistors, solar cells, rectifiers and other instruments.

Biological role

Silicon is essential to plant and animal life. It is perhaps as important to humans, in whom it is found in connective tissue and skin. It 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 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. Silicon is prepared commercially by electrolysis with carbon electrodes of a mixture of silica and carbon. Silicon is used extensively in solid-state devices, and for this hyperpure silicon is required before tiny controlled amounts of specific impurities are added. This is prepared by thermal decomposition of ultra-pure trichlorosilane. Every year, 5,000 tonnes of semiconductor-grade silicon and 500,000 tonnes of metallurgy-grade silicon are produced.

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, E_d in eV. χ_A - χ_B =(eV)-1/2sqrt(E_d(AB)-[E_d(AA)+E_d(BB)]/2), with χ_H set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).

1^st 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)	1^st 786.518 2^nd 1577.133 3^rd 3231.583 4^th 4355.519 5^th 16090.557 6^th 19805.529 7^th 23783.616 8^th 29287.135

Bonding and Enthalpies terminology

Covalent Bonds
The strengths of several common covalent bonds.

Bonding / Enthalpies

Covalent bonds

H–Si 318 kJ mol ^-1	H–Si 364 kJ mol ^-1	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

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.

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

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1400

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2200

2400

Pressure (Pa)

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Podcasts

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Video

Videos of the elements. Additional videos will be coming in 2012.

Help Text

Resources

Making silicon and silanes

Description :

The reactions of group IV elements

Faces of Chemistry: Organic solar cells

Description :

Ingmar Bruder, a scientist from BASF, explains the science involved in organic photovoltaics (organic solar cells) used in the Smart Forvision car.

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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.
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.

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