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 18  Melting point -71 oC, -95.8 oF, 202.15 K 
Period Boiling point -61.7 oC, -79.06 oF, 211.45 K 
Block Density (kg m-3) 440 (liquid 211 K) 
Atomic number 86  Relative atomic mass 222.018  
State at room temperature Gas  Key isotopes 211Rn, 220Rn, 222Rn 
Electron configuration [Xe] 4f145d106s26p6  CAS number 10043-92-2 
ChemSpider ID 23240 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
Imagery based around the familiar radiation hazard symbol. The background “home” symbols reflect the detectable amounts of the element that can build up in houses.
Appearance
Radon was first discovered as the gas produced from radium as it decayed in sealed ampoules. It is colourless and odourless, and is chemically inert, but it is dangerous because it gives off alpha rays. There is a detectable amount in the atmosphere, and concentrations can build up indoors in certain localities.
Uses
Radon decays into radioactive polonium and alpha rays, and this emitted radiation made radon useful in cancer therapy. The gas was sealed in minute tubes called seeds or needles, and implanted into the tumour. The diseased tissue was thus destroyed in situ by the radiation.
Biological role
Radon has no known biological role. It is toxic due to its radioactivity, the main hazard arising from inhalation, as the element and its radioactive daughters collect on dust particles.
Natural abundance
Radon is produced naturally from the decay of a radium isotope, 226Ra. It was first discovered as the gas produced from radium as it decayed in sealed ampoules. There is a detectable amount in the atmosphere, and concentrations can build up indoors in certain localities.
 
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) 2.200 Covalent radius (Å) 1.46
Electron affinity (kJ mol-1) Not stable Electronegativity
(Pauling scale)
Unknown
Ionisation energies
(kJ mol-1)
 
1st
1037.072
2nd
-
3rd
-
4th
-
5th
-
6th
-
7th
-
8th
-
 

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 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  211Rn 210.991 - 14.6 h  β+,EC 
        α 
  220Rn 220.011 - 55.6 s  α 
  222Rn 222.018 - 3.823 d  α 
 

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)
20.786 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - - - - - - -
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History

In 1899, Ernest Rutherford and Robert B. Owens detected a radioactive gas being released by thorium. That same year, Pierre and Marie Curie detected a radioactive gas emanating from radium. In1900, Friedrich Ernst Dorn at Halle, Germany, noted that a gas was accumulating inside ampoules of radium. They were observing radon. That from radium was the longer-lived isotope radon-222 which has a half-life 3.8 days, and was the same isotope which the Curies has observed. The radon that Rutherford detected was radon-220 with a half-life of 56 seconds.


In 1900, Rutherford devoted himself to investigating the new gas and showed that it was possible to condense it to a liquid. In 1908, William Ramsay and Robert Whytlaw-Gray at University College, London, collected enough radon to determine its properties and reported that it was the heaviest gas known.

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Podcasts

Listen to Radon Podcast
Transcript :

Chemistry in its Element - Radon


(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)

 

Chris Smith

 

This week residents of Aberdeen, Edinburgh and Cornwall, watch out, Radon's about.

  

 

Katherine Holt

 

When I bought my house recently I was intrigued by a comment in the surveyors report which stated 'higher than the actionable levels of radioactive radon gas have been found in up to 10% of dwellings in this area of the country and we recommend the property be tested for the levels of radon.' Well of course in the flurry of activity associated with moving I didn't think about this for some time but recently I started to read more about this mysterious radioactive gas which may be invading my property! 

 

The first reports of problems associated with radon gas in domestic buildings was in the United States in 1984, when an employee at a nuclear power plant began setting off the radiation detector alarms on his way into work. The problem was eventually traced to his home, where the level of radon gas in his basement was found to be abnormally high. Radon emanates directly from the ground all over the world but especially in regions with high levels of granite or shale in the soil. Uranium, a relatively common constituent of soils, decays to form radium, which in turn decays to produce radon. In fact for most UK residents, naturally occurring radon accounts for half of their annual radiation dosage. However it only really becomes problematic when high levels are produced in confined spaces, for example the ground floor of buildings without adequate ventilation.   Some homes in Cornwall, where the ground has high granite content, were found to contain worrying levels of radon. However forced ventilation methods largely remove the problem.  

 

Radon is the product of the decay of other unstable, radioactive elements such as radium, thorium and actinium. The colourless, odourless, tasteless gas can be isolated from these sources but soon decays as it has no stable isotopes. The early pioneers in the study of radioactivity, the Curies, had noted that radium appeared to make the surrounding air radioactive. The discovery of radon is credited to a German physicist Friedrich Ernst Dorn, who traced this observed radioactivity to a gas which was given off by radium - a gas which he called 'radium emanation'. Similar 'emanations' were isolated from other elements - for example thorium, and eventually the gas was identified as the heaviest of the noble gases, named radon, and given its rightful place in the periodic table. 

 

Not much research has been carried out on radon, due to its radioactivity, but it is largely un-reactive with few known compounds. Like the other noble gases it has been found to form compounds with fluorine. It is the densest known gas, another reason why it tends to linger in low-lying confined spaces. Below its boiling point it forms a colourless liquid and then at lower temperatures an orange-red solid which glows eerily due to the intense radiation it produces.  

 

Radon has a fairly short half-life of only a few days so rapidly decays. Why then should we worry about radon levels in our homes?   The problem is, when breathed in, it can decay to form other, longer-lasting, solid radioactive species, which can coat the lungs, leading to continual exposure. These so-called 'radon daughters' include polonium-214, polonium-218 and lead-214 - not family members you'd wish to spend a lot of time with. Prolonged radon exposure is believed to be the second most frequent cause of lung cancer after smoking. The unfortunate gentleman with the basement full of radon had a risk of consequentially developing lung cancer equivalent to smoking 135 packs of cigarettes every day! 

 

So now that I'm comfortable in my freshly decorated new home, all that remains for me to do is to check that my surroundings are as safe as they look. Fortunately that's easily done these days with radon test kits which you can order online. You place them in the corner of a room for three months and forget about them and then send them away to be analysed. OK, so it costs £30 quid or so - but that's a small price to pay for peace of mind.     

 

Chris Smith

But maybe don't take a deep breath before you open the results from the lab, just in case.   That was UCL Chemist Katherine Holt, with the story of the radio active resident in your basement.   Next week from a chemical that kills silently and slowly to an albeit more fearsome beast.

 

Kira Weissman

The 37-year old technician spilled only a few hundred millilitres or so in his lap during a routine palaeontology experiment.   He took the normal precaution in such situations, quickly dowsing himself with water from a laboratory hose, and even plunged into a nearby swimming pool while the paramedics were en route.   But a week later, doctors removed a leg, and a week after that, he was dead.   The culprit: hydrofluoric acid (colloquially known as HF), and the unfortunate man was not its first victim.  

Chris Smith

But what killed him, and what about the people who first isolated HF, unaware of its terrible reputation?   Well you can find out what happened to them from Kira Weissman on next week's Chemistry in its Element.   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. 

(End promo)

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Resources

Description :
The activity sets some critical thinking and pattern spotting tasks in the context of the noble gases. The students are given data that can be manipulated to show a directly proportional relationship,...
Description :
A teaching resource on Group 8 (18) - The Noble Gases, supported by video clips from the Royal Institution Christmas Lectures® 2012.
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We discover how to extract lead from lead(II) oxide. We mix lead(II) oxide with charcoal powder and then heat the mixture using a Bunsen burner. It glows bright red as a reaction occurs and after a fe...
Learn Chemistry: Your single route to hundreds of free-to-access chemistry teaching resources.
 

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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.