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.

Oxygen

Discovery date	1774
Discovered by	Joseph Priestley in Wiltshire, England and independently by C.W. Scheele in Uppsala, Sweden
Origin of the name	The name comes from the Greek 'oxy genes', meaning acid forming.
Allotropes	O₂, O₃

15.999

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	16	Melting point	-218.79 ^oC, -361.822 ^oF, 54.36 K
Period	2	Boiling point	-182.962 ^oC, -297.332 ^oF, 90.188 K
Block	p	Density (kg m^-3)	1460 (20.5 K)
Atomic number	8	Relative atomic mass	15.999
State at room temperature	Gas	Key isotopes	¹⁶O
Electron configuration	[He] 2s²2p⁴	CAS number	7782-44-7
ChemSpider ID	140526	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

Ozone and iced water. An image representing the fundamental importance of the element in air and water.

Appearance

A colourless, odourless gas that makes up 21% of the atmosphere, which is half-way between 17% (below which breathing for unacclimatised poeple becomes difficult) and 25% (above which many organic compounds, like Teflon, are highly flammable). The element is essential for all forms of life since it is a constituent of DNA, and it comprises over half the mass of the average person. Indeed it is the most common element in the Earth’s crust, in the form of silicon-oxygen minerals, and in the sea since it accounts for 89% of the mass of water. Oxygen gas is fairly soluble in water, which makes life in rivers, lakes and oceans possible. We breathe in oxygen so that it can react with energy stores in our bodies to provide the heat and motion that keeps us alive, and we return it to the atmosphere as carbon dioxide. Industrially, oxygen is produced on a large scale from liquid air, and used for steel making, metal cutting (oxy-acetylene torches) and by the chemicals industry.

Uses

Oxygen is very reactive and capable of combining with most other elements. It is a component of thousands of organic compounds, and is essential for the respiration of all plants and animals and for almost all combustion. Indeed it is the most common element in the Earth’s crust, in the form of silicon-oxygen minerals, and in the sea since it accounts for 89% of the mass of water. The greatest commercial use of gaseous oxygen is oxygen enrichment of steel blast furnaces. Large quantities are also used in making synthesis gas for ammonia and methanol, ethylene oxide, and for oxy-acetylene welding and cutting of metals. Large amounts of gas are also used by the electronics industry, which uses the gas as a blanketing.

Biological role

Oxygen is the basis of all life since it is a constituent of DNA, and it comprises over half the mass of the average person. We breathe in oxygen so that it can react with energy stores in our bodies to provide the heat and motion that keeps us alive, and we return it to the atmosphere as carbon dioxide. It is restored to the air by the photosynthesis mechanism of plants. Oxygen gas is fairly soluble in water, which makes life in rivers, lakes and oceans possible.

Natural abundance

Oxygen, as a gaseous element, forms 21% of the atmosphere by volume which is half-way between 17% (below which breathing for unacclimatised people becomes difficult) and 25% (above which many organic compounds, like Teflon, are highly flammable). Oxygen can be obtained by liquefaction and fractional distillation. The element and its compounds make up 49.2%, by mass, of the Earth’s crust. About two-thirds of the human body and nine-tenths of water is oxygen. In the laboratory it can be prepared by the electrolysis of water or by adding manganese(IV) oxide as a catalyst to aqueous hydrogen peroxide.

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)	1.520	Covalent radius (Å)	0.64
Electron affinity (kJ mol^-1)	140.926	Electronegativity (Pauling scale)	3.440
Ionisation energies (kJ mol^-1)	1^st 1313.942 2^nd 3388.668 3^rd 5300.466 4^th 7469.264 5^th 10989.574 6^th 13326.515 7^th 71330.586 8^th 84078.228

Bonding and Enthalpies terminology

Covalent Bonds
The strengths of several common covalent bonds.

Bonding / Enthalpies

Covalent bonds

H–O 464 kJ mol ^-1	N–O 214 kJ mol ^-1	N=O 587 kJ mol ^-1
O–O 144 kJ mol ^-1	O–O 302 kJ mol ^-1	O=O 498.3 kJ mol ^-1
O=S 469 kJ mol ^-1	O–Si 466 kJ mol ^-1	O=Si 638 kJ mol ^-1
O≡Si 805 kJ mol ^-1	C–O 358 kJ mol ^-1	C–O 336 kJ mol ^-1
C=O 805 kJ mol ^-1	C=O 695 kJ mol ^-1	C=O 736 kJ mol ^-1
C=O 749 kJ mol ^-1	C≡O 1077 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 (%)	n/a
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	-1, -2
Isotopes	Isotope	Atomic mass	Natural abundance (%)	Half life	Mode of decay
	¹⁶O	15.995	99.757	-	-
	¹⁷O	16.999	0.038	-	-
	¹⁸O	17.999	0.205	-	-

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)

29.378

Young's modulus (GPa)

Unknown

Shear modulus (GPa)

Unknown

Bulk modulus (GPa)

Unknown

Vapour pressure

Temperature (K)

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Pressure (Pa)

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Podcasts

Chemistry World podcast

Chemistry World podcast transcript

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Video

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

Terms & Conditions

Images © Murray Robertson 1999-2011
Text © The Royal Society of Chemistry 1999-2011

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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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