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.



A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

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.

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.

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 15  Melting point Sublimes at 616°C, 1141°F, 889 K 
Period Boiling point Sublimes at 616°C, 1141°F, 889 K 
Block Density (g cm−3) 5.75 
Atomic number 33  Relative atomic mass 74.922  
State at 20°C Solid  Key isotopes 75As 
Electron configuration [Ar] 3d104s24p3  CAS number 7440-38-2 
ChemSpider ID 4514330 ChemSpider is a free chemical structure database


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.


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
Prawns contain quite high levels of arsenic, in an organoarsenic form which is not harmful to health.
Arsenic is a semi-metal. In its metallic form it is bright, silver-grey and brittle.
Arsenic is a well-known poison. Arsenic compounds are sometimes used as rat poisons and insecticides but their use is strictly controlled.

Surprisingly, arsenic can also have medicinal applications. In Victorian times, Dr Fowler’s Solution (potassium arsenate dissolved in water) was a popular cure-all tonic that was even used by Charles Dickens. Today, organoarsenic compounds are added to poultry feed to prevent disease and improve weight gain.

Arsenic is used as a doping agent in semiconductors (gallium arsenide) for solid-state devices. It is also used in bronzing, pyrotechnics and for hardening shot.

Arsenic compounds can be used to make special glass and preserve wood.
Biological role
Some scientists think that arsenic may be an essential element in our diet in very, very low doses. In small doses it is toxic and a suspected carcinogen. Once inside the body it bonds to atoms in the hair, so analysing hair samples can show whether someone has been exposed to arsenic. Some foods, such as prawns, contain a surprising amount of arsenic in a less harmful, organic form.
Natural abundance
A small amount of arsenic is found in its native state. It is mainly found in minerals. The most common arsenic-containing mineral is arsenopyrite. Others include realgar, orpiment and enargite. Most arsenic is produced as a by-product of copper and lead refining. It can be obtained from arsenopyrite by heating, causing the arsenic to sublime and leave behind iron(II) sulfide.
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Arsenic was known to the ancient Egyptian, and is mentioned in one papyrus as a ways of gilding metals. The Greek philosopher Theophrastus knew of two arsenic sulfide minerals: orpiment (As2S3) and realgar (As4S4). The Chinese also knew about arsenic as the writings of Pen Ts’ao Kan-Mu. He compiled his great work on the natural world in the 1500s, during the Ming dynasty. He noted the toxicity associated with arsenic compounds and mentioned their use as pesticides in rice fields.

A more dangerous form of arsenic, called white arsenic, has also been long known. This was the trioxide, As2O3, and was a by-product of copper refining. When this was mixed with olive oil and heated it yielded arsenic metal itself. The discovery of the element arsenic is attributed to Albertus Magnus in the 1200s.

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) 1.85 Covalent radius (Å) 1.20
Electron affinity (kJ mol−1) 77.574 Electronegativity
(Pauling scale)
Ionisation energies
(kJ mol−1)

Bond enthalpy (kJ mol−1)
A measure of how much energy is needed to break all of the bonds of the same type in one mole of gaseous molecules.

Bond enthalpies

Covalent bond Enthalpy (kJ mol−1) Found in
H–As 247 AsH3


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.


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, 3, -3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  75As 74.922 100


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.


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 7.6
Crustal abundance (ppm) 2.5
Recycling rate (%) <10
Substitutability Unknown
Production concentration (%) 64
Reserve distribution (%) Unknown
Top 3 producers
  • 1) China
  • 2) Chile
  • 3) Kazakhstan
Top 3 reserve holders
  • Unknown
Political stability of top producer 24.1
Political stability of top reserve holder Unknown


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)
329 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) 22
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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Listen to Arsenic Podcast
Transcript :

Chemistry in its element: arsenic

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, poisons in paint, fireworks and aphrodisiacs, Napoleon's wallpaper and the whiff of garlic, what's the link? Here is Bea Perks.

Bea Perks

Mention arsenic to anyone even a chemist, the first word that is likely to come to mind is poison, it is of course a deadly poison, but its compounds also found or have been found in insecticides, colouring agents, wood preservatives, in animal feed, as a treatment for syphilis, and treatments for cancer, as a treatment for psoriasis, in fireworks and as a semiconductor. Oh! Just may be as an aphrodisiac.

Arsenic, atomic number 33 lies in between phosphorus and antimony in group 15, the so called Nitrogen group of the periodic table. Members of the group including of course nitrogen, along with arsenic, phosphorous, antimony and bismuth are particularly stable in compounds because they tend to form double or triple covalent bonds. The property also leads to toxicity particularly evident in phosphorus, antimony and most notoriously, arsenic. When they react with certain chemicals in the body they create strong free radicals that are not easily processed by the liver where they accumulate.

Arsenic is neither a metal nor a non-metal but instead joins a select but rather ill defined group of elements called the metalloids. These are found in the periodic table along a diagonal line from Boron at the top left to round about polonium at the bottom right. Everything to the right of the line in the periodic table is a non-metal and everything to the left is a metal. The exact members of the group are open to debate but arsenic is always a member. Most metalloids occur in several forms or allotropes where one might seem metallic while another one seems non-metallic. Carbon isn't a metalloid because despite the semiconductor properties of graphite all of its allotropes from graphite to diamond are non-metallic in character.

Arsenic gets its name from a Persian word for the yellow pigment now known as orpiment. For keen lexicographers apparently the Persian word in question Zarnikh was subsequently borrowed by the Greeks for their word arsenikon which means masculine or potent.

Orpiment or yellow arsenic trisulphide is a historical pigment identified in ancient Egyptian artefacts. On the pigment front they were hardly dare mentioned it, such a well worn tale, Napoleon's wallpaper just before his death is reported to have incorporated a so called Scheele's green which exuded an arsenic vapour when it got damp. All well and good except that Napoleon also suffered from stomach ulcers, gastric cancer, tuberculosis, etc etc, so make of it what you will!

Arsenic doesn't seem much like a metal in its so called yellow form, but it also has a grey form known tellingly as metallic arsenic. Yellow arsenic has a specific gravity of 1.97 while grey arsenic has a specific gravity of 5.73. Grey arsenic is the usual stable form with a melting point of 817 degree Celsius. It is a very brittle semi-metallic solid, steel grey in colour that tarnishes readily in air. It's rapidly oxidized to arsenous oxide which smells of garlic if you are brave enough to smell it when you heat it.

In the days when deliberate arsenic poisoning remained a real threat and before the arrival of tests that could alert the authorities to its presence. Poisoning was some times diagnosed on the basis of a victim's garlic breath. In a curious twist far more recently, researchers in India showed that eating 1 to 3 cloves of garlic a day could protect people from the arsenic poisoning associated with contaminated drinking water.

The reappearance of garlic is coincidental and the type of poisoning, acute deliberate poisoning versus unintentional long term poisoning by drinking water is very different. Arsenic levels in ground water are sometimes elevated as a result of erosion from local rocks. There's a particular problem in Bangladesh, rising arsenic levels there followed what was supposed to be an improvement to the water supply. Local populations used to get their drinking water from open sources like ponds. But about 30 years ago they started getting water from wells. Well digging saw a marked decrease in water borne infections. By 1993 it was discovered that arsenic was present in these wells. The first symptoms found in people drinking arsenic contaminated water include pigmentation changes in the skin and skin thickening or hyperkeratosis. After about 10 years drinking that water symptoms extend to skin and internal cancers. The World Health Organization report that arsenic in drinking water could end up causing between 200,000 to 270,000 deaths in Bangladesh from cancer. Arsenic levels appear to be lower in shallower, ground water or in much deeper aquifers and this knowledge should hopefully contribute to reducing the risks in future.

On a lighter note, I'm afraid there isn't much evidence despite its link with the Greek word for potent that arsenic is an aphrodisiac. It's a shame because it might have been rather useful if it was. An arsenic-based drug called Salvarsan was developed in 1910 by Nobel laureate Paul Ehrlich to treat the sexually transmitted disease syphilis.

Chris Smith

Chemistry world's Bea perks on the science of element number 33, arsenic. And if you think arsenic is nasty, wait till you meet next week's element

Peter Wothers

It sounds like a Doctor Who monster and in a number of ways this element does have a few properties that would make it suitable for any good, outer space sci-fi horror movie. For a start, like many space monsters it comes from slime. Every good monster must have a secret weapon and tellurium is no exception. It gives its enemies garlic breath. Really bad garlic breath.

Chris Smith

Nice! That was Peter Wothers who will be here to tell the tale of the smelly element tellurium on next week's Chemistry in its element. I hope you can join us. I'm Chris Smith, thank you for listening and goodbye.


Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by There's more information and other episodes of Chemistry in its element on our website at

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Visual Elements images and videos
© Murray Robertson 1998–2017.



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 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
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

Elements 1–112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.



Produced by The Naked Scientists.


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