Periodic Table > Arsenic
 

Terminology


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


For more information on Murray Robertson’s image see Uses and properties 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 15  Melting point 616 oC, 1140.8 oF, 889.15 K 
Period Boiling point Sublimes 
Block Density (kg m-3) 5776 
Atomic number 33  Relative atomic mass 74.922  
State at room temperature Solid  Key isotopes 75As 
Electron configuration [Ar] 3d104s24p3  CAS number 7440-38-2 
ChemSpider ID 4514330 ChemSpider is a free chemical structure database
 

Uses and properties 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 and properties

 
Image explanation
Prawns are known to contain quite high levels of arsenic.
Appearance

A bright silver-grey brittle semi-metal.

Uses

Arsenic is used in bronzing, pyrotechnics and for hardening shot. It is increasingly being used as a doping agent in semi-conductors (gallium arsenide) for solid state devices. Although it is now strongly linked with poison, arsenic was once used widely as a medicine. Dr Fowler’s Solution (potassium arsenate dissolved in water) was a popular cure-all tonic in Victorian times - even Charles Dickens used it. Arsenic compounds are also employed in making special glass and preserving wood.

Biological role

Arsenic may be an essential element in very low doses in our diet, claimed by some scientists, but it is certainly toxic in small doses and also a suspected carcinogen. Calcium and lead arsenic compounds are used as poisons for vermin. Nowadays its use is strictly controlled, Some foods such as prawns contain a surprising amount of arsenic.

Natural abundance

The most common arsenic-containing mineral is mispickel, and others include realgar and orpiment. Arsenic can also be found in the native state. It can be obtained from mispickel by heating, which causes the arsenic to sublime and leaves the iron(II) sulfide.

 
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) 1.850 Covalent radius (Å) 1.2
Electron affinity (kJ mol-1) 77.574 Electronegativity
(Pauling scale)
2.180
Ionisation energies
(kJ mol-1)
 
1st
944.456
2nd
1793.584
3rd
2735.454
4th
4836.806
5th
6042.872
6th
12311.519
7th
-
8th
-
 
Bond enthalpies terminology

Covalent Bonds
The strengths of several common covalent bonds.

Bond enthalpies

 
Covalent bonds
H–As  297  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 6.0
Country with largest reserve base n/a
Crustal abundance (ppm) 2.5
Leading producer China
Reserve base distribution (%) n/a
Production concentration (%) 61.90
Total governance factor(production) 5
Top 3 countries (mined)
  • 1) n/a
Top 3 countries (production)
  • 1) China
  • 2) Chile
  • 3) Kazakhstan
 

Oxidation states and 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 and isotopes

 
Common oxidation states 5, 3, -3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  75As 74.922 100
 

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 and temperature data – advanced

 
Molar heat capacity
(J mol-1 K-1)
24.64 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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History

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.

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Podcasts

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 elements. I hope you can join us. I'm Chris Smith, thank you for listening and goodbye.  

 

(Promo)

 

Chemistry in its elementis 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. 

 

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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.