Glossary


Allotropes
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.

 

Glossary


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


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


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 (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.


Sublimation
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.


Isotopes
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 Melting point 727°C, 1341°F, 1000 K 
Period Boiling point 1845°C, 3353°F, 2118 K 
Block Density (g cm−3) 3.62 
Atomic number 56  Relative atomic mass 137.327  
State at 20°C Solid  Key isotopes 138Ba 
Electron configuration [Xe] 6s2  CAS number 7440-39-3 
ChemSpider ID 4511436 ChemSpider is a free chemical structure database
 

Glossary


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.


Appearance

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
The image is based on x-ray radiographs of the human stomach and intestines in patients who have been given a ‘barium meal’.
Appearance
Barium is a soft, silvery metal that rapidly tarnishes in air and reacts with water.
Uses
Barium is not an extensively used element. Most is used in drilling fluids for oil and gas wells. It is also used in paint and in glassmaking.

All barium compounds are toxic; however, barium sulfate is insoluble and so can be safely swallowed. A suspension of barium sulfate is sometimes given to patients suffering from digestive disorders. This is a ‘barium meal’ or ‘barium enema’. Barium is a heavy element and scatters X-rays, so as it passes through the body the stomach and intestines can be distinguished on an X-ray.

Barium carbonate has been used in the past as a rat poison. Barium nitrate gives fireworks a green colour.
Biological role
Barium has no known biological role, although barium sulfate has been found in one particular type of algae. Barium is toxic, as are its water- or acid-soluble compounds.
Natural abundance
Barium occurs only in combination with other elements. The major ores are barite (barium sulfate) and witherite (barium carbonate). Barium metal can be prepared by electrolysis of molten barium chloride, or by heating barium oxide with aluminium powder.
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History

In the early 1600s, Vincenzo Casciarolo, of Bologna, Italy, found some unusual pebbles. If they were heated to redness during the day, they would shine during the night. This was the mineral barite (barium sulfate, BaSO4).

When Bologna stone, as it became known, was investigated by Carl Scheele in 1760s he realised it was the sulfate of an unknown element. Meanwhile a mineralogist, Dr William Withering, had found another curiously heavy mineral in a lead mine in Cumberland which clearly was not a lead ore. He named it witherite; it was later shown to be barium carbonate, BaCO3.

Neither the sulfate nor the carbonate yielded up the metal itself using the conventional process of smelting with carbon. However, Humphry Davy at the Royal Institution in London produced it by the electrolysis of barium hydroxide in 1808.
 
Glossary

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) 2.68 Covalent radius (Å) 2.06
Electron affinity (kJ mol−1) 13.954 Electronegativity
(Pauling scale)
0.89
Ionisation energies
(kJ mol−1)
 
1st
502.849
2nd
965.223
3rd
-
4th
-
5th
-
6th
-
7th
-
8th
-
 

Glossary


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.


Isotopes

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 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  130Ba 129.906 0.106 2.2 x 1021 β+β+ 
  132Ba 131.905 0.101 1.3 x 1021 EC EC 
  134Ba 133.905 2.417
  135Ba 134.906 6.592
  136Ba 135.905 7.854
  137Ba 136.906 11.232
  138Ba 137.905 71.698
 

Glossary

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.


Substitutability

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 8.1
Crustal abundance (ppm) 456
Recycling rate (%) <10
Substitutability High
Production concentration (%) 44
Reserve distribution (%) 42
Top 3 producers
  • 1) China
  • 2) India
  • 3) USA
Top 3 reserve holders
  • 1) China
  • 2) India
  • 3) Algeria
Political stability of top producer 24.1
Political stability of top reserve holder 24.1
 

Glossary


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)
204 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)
- 7.97
x 10-6
0.045 7.11 162 - - - - - -
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Podcasts

Listen to Barium Podcast
Transcript :

Chemistry in its element: barium


(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

Hello, this week rat poison, fireworks, fine glass, oil exploration and enemas. Spotted the link yet, well the answer is sitting in the apple green element at the bottom of group two.

Adina Payton

For many, barium has an unpleasant association. The first thing most people think about when this element is mentioned is the "barium enema" or "barium swallow". Sickly memories often surface of the radiology clinic - where they even ask which flavor you would like strawberry or banana... These "cocktails" consist of a white fluid of barium sulfate that is either "squirted" up one orifice or swallowed down another. It is used to help diagnose diseases and other problems that affect the large intestine or the esophagus. The heavy barium blocks X-rays, causing the filled part of the digestive system to show up clearly on the X-ray picture or CT scan. Barium sulfate can be taken into our body because it is highly insoluble in water, and is eliminated completely from the digestive tract. And if this sounds like an unpleasant experience, it's lucky that it's barium sulfate and not just barium that is used for the exam.

Barium is a highly toxic metal. It's extremely poisonous - no one in their right mind would consider consuming it. At low doses, it acts as a muscle stimulant, while higher doses play havoc with the nervous system, causing an irregular heartbeat, tremor, weakness, anxiety, paralysis, and potentially death as the heart and lungs fail. Acute doses of less than 1 gram can be fatal to humans. Indeed barium carbonate is useful as rat poison. Unlike barium sulfate, barium carbonate dissolves in stomach acid, releasing the poisonous barium to do its rather nasty but efficient work.

Conveniently barium, which is a soft silvery metallic alkaline earth metal, is never found in nature in its pure form, due to its reactivity with air or in water. In fact the metal is a "getter" in vacuum tubes, meaning it's used to remove the last traces of oxygen.

Barium compounds are notable for their high specific gravity - which, in practical terms, means the compounds are extremely heavy. This is true of the most common barium-bearing mineral, its sulfate - barite BaSO4 - is called 'heavy spar' due to the high density (4.5 g/cm³ - the size of a pea). Indeed the name barium comes from the Greek barys, meaning "heavy". Due to its density barium compounds, and especially barite (BaSO4), are extremely important to the petroleum industry. Barite is used in drilling mud, a weighting agent in drilling new oil wells.

Barium carbonate also has an application that is more appealing than rat poison - it's used in glassmaking to enhance the luster of the glass. And barite is used in paints, bricks, tiles, glass and rubber production; barium nitrate and chlorate give green colors to fireworks and barium titanate was proposed in 2007 to be used in next generation battery technology for electric cars. Despite the relative high abundance of barium sulfate in nature - it's the 14th most abundant element in earths crust - due to its multiple uses it has a high value, in the range of $55/100grams. Total annual world production is estimated at around 6,000,000 tons. And the main mining areas are the UK, Italy, the Czech Republic, USA and Germany. Total world reserves are estimated to be around 450,000,000 tons.

And why am I so particularly interested in this heavy, poisonous element? Well, as a scientist I actually study barite - I separate barite from marine sediments - the mud at the bottom of the sea - and analyze its chemistry which tells us fabulous stories about seawater chemistry and productivity in the geological past. Barite forms in proportion to ocean productivity - the activity of marine phytoplankton the floating "trees" of the ocean which are the base of the marine food chain - and accumulates in marine sediments. The accumulation of barite in ocean sediments can tell us how productive the ocean was at any given time in Earth's history. Barite in contrast to many other minerals is not soluble and is preserved over many millions of years recording the chemistry of the ocean and how it changed over time.

And therefore it's a great archive of ocean history.

Chris Smith

Chemist Adina Payton telling the tale of barium. And talking of what sits at the bottom of the oceans.

Steve Mylon

"How did it smell?" That was the only question I needed to ask a geologist colleague of mine about the sediment she was trying to understand. The smell of the sediment tells a great deal about the underlying chemistry. Thick black anoxic sediments can be accompanied by a putrid smell which is unique to reduced sulfur.

Maybe this is why sulfur has such a bad reputation. My son wouldn't eat eggs for 6 months when he got a smell of his first rotten one.

Chris Smith

That's the stinky story of sulfur with Steve Mylon on next week's Chemistry in its element, I hope you can join us. I'm Chris Smith, thank you for listening and goodbye.

(Promo)

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements.

(End promo)
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References

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

 

Data

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.

 

Podcasts

Produced by The Naked Scientists.

 

Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.
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