Barium Element Facts

The chemical element barium is classed as an an alkali earth metal. It was discovered in 1774 by Carl W. Scheele.

Barium. Photo by Matthias Zepper.

Data Zone

Classification: Barium is an alkali earth metal
Color: silvery white
Atomic weight: 137.33
State: solid
Melting point: 725 oC, 998.2 K
Boiling point: 1897 oC, 2170 K
Electrons: 56
Protons: 56
Neutrons in most abundant isotope: 82
Electron shells: 2,8,18,18,8,2
Electron configuration: [Xe] 6s2
Density @ 20oC: 3.59 g/cm3
Show more, including: Heats, Energies, Oxidation, Reactions, Compounds, Radii, Conductivities
Atomic volume: 39.24 cm3/mol
Structure: bcc: body-centered cubic
Hardness: 1.25 mohs
Specific heat capacity 0.204 J g-1 K-1
Heat of fusion 7.12 kJ mol-1
Heat of atomization 182 kJ mol-1
Heat of vaporization 140.3 kJ mol-1
1st ionization energy 502.9 kJ mol-1
2nd ionization energy 965.2 kJ mol-1
3rd ionization energy 3600 kJ mol-1
Electron affinity 14 kJ mol-1
Minimum oxidation number 0
Min. common oxidation no. 0
Maximum oxidation number 2
Max. common oxidation no. 2
Electronegativity (Pauling Scale) 0.89
Polarizability volume 39.7 Å3
Reaction with air vigorous, w/ht ⇒ BaO, Ba2N3
Reaction with 15 M HNO3 mild, ⇒ Ba(NO3)2
Reaction with 6 M HCl vigorous, ⇒ H2, BaCl2
Reaction with 6 M NaOH passivated
Oxide(s) BaO, BaO2
Hydride(s) BaH2
Chloride(s) BaCl2
Atomic radius 215 pm
Ionic radius (1+ ion)
Ionic radius (2+ ion) 149 pm
Ionic radius (3+ ion)
Ionic radius (1- ion)
Ionic radius (2- ion)
Ionic radius (3- ion)
Thermal conductivity 18.4 W m-1 K-1
Electrical conductivity 2.8 x 106 S m-1
Freezing/Melting point: 725 oC, 998.2 K


Barium was first discovered in barite, also known as barium sulfate. This mineral attracted attention in the 17th century, when it was found to radiate red light after heating. Image from Missouri Dept. of Natural Resources.

Phosphorescent Toy

When Vincentius Casciorolus saw rocks that glowed in the dark, he thought he might be looking at the philosopher’s stone. Nowadays, nearly everyone has seen phosphorescent materials in action. Image by Luu Ly.

Discovery of Barium

Dr. Doug Stewart

In the early 1600s, Vincentius Casciorolus, a shoemaker with an interest in alchemy was excited. In the mountains near Bologna, Italy he had learned there was a heavy silvery-white mineral with remarkable properties – perhaps, he thought, it might even be the philosopher’s stone.

When the mineral was heated and combusted, the product emitted a phosphorescent red glow – nice, but what really excited Casciorolus – and others – was that if the combusted material was exposed to sunshine, it would glow in the dark for up to an hour afterwards.

We now know that the silvery white mineral was impure barium sulfate, BaSO4. After heating, it became impure barium sulfide, BaS. (1), (2), (3), (4)

Sadly for Casciorolus, although this material’s properties were interesting, it proved useless as a means of making gold from other metals and failed to make him immortal. Rather than ‘philosopher’s stone’ it became known as ‘Bologna stone’ – a curiosity.

Sadly, also, no-one took the opportunity to discover the new element present in Bologna stone. Of course, at the time, nobody suspected there were any new elements to be discovered!

About 170 years passed before barium was first recognized as a new element by Swedish scientist Carl W. Scheele. Investigating magnesium oxide in 1774, Scheele found a new earth metal: “an earth differing from all earths hithero known.” He called this new metal ‘terra ponderosa.’ (Latin: heavy earth.)

A comparison was made with Bologna stone, and the two were found to contain the same substance. (Until this point, people had thought Bologna stone was a compound of calcium. (2))

Barium metal was isolated for the first time in 1808 by English chemist Sir Humphrey Davy in London. Davy followed the advice of Swedish chemist Jons Jacob Berzelius, who had told him that barium sulfate could be decomposed by electrolysis. This was correct, and Davy isolated strontium in a similar way. The experimental details are on our strontium page.

The element was called barium because it was found in barite (barium sulfate) a mineral given its name because of its high density. The Greek ‘barys’ means heavy.

Barium’s Periodic Table Neighborhood

Barium sits close to the bottom of the periodic table’s Group 2. It is Group 2’s final stable element. Radium, which follows, is radioactive. Group 2 elements are sufficiently reactive that the free metals are never found naturally; they are, however, much less reactive that Group 1 metals. In general, reactivity increases as one looks down Group 2; so barium is more reactive than strontium and calcium, for example.

Barium is used in medicine to detect abnormalities in the digestive system.

The reaction between ammonium thiocyanate and barium hydroxide octahydrate is endothermic. As a result, the temperature will drop quickly. This causes the beaker to freeze to the wooden board.


Appearance and Characteristics

Harmful effects:

Barium compounds that are water or acid soluble are highly poisonous. Barium powder can ignite spontaneously in air.

Barium sulfate, used in x-ray imaging, is highly insoluble in water, and is therefore nontoxic and completely removed from the digestive tract.


Barium is a metallic element chemically resembling calcium but more reactive. It is a soft, silvery metal and when cut it quickly turns a black color due to the formation of barium oxide, (BaO).

It is also highly reactive with water or alcohol.

When present in compounds barium exists usually in the Ba2+, divalent state.

Barium dissolves in most aqueous acids except sulfuric acid, due to the formation of an insoluble protective layer of barium sulfate.

Barium is most commonly found as the mineral barite (BaSO4) and witherite (BaCO3)

Uses of Barium

Barium is used as a “flashed getter” in vacuum tubes to remove the last traces of gases.

Barium is an important element in yttrium barium copper oxide (YBCO) superconductors.

An alloy of barium with nickel is used in sparkplug wire.

Barium sulfate (barite) is used to increase the contrast in x-ray imaging of the digestive system.

Abundance and Isotopes

Abundance earth’s crust: 425 parts per million by weight, 41 parts per million by moles

Abundance solar system: parts per billion by weight, parts per billion by moles

Cost, pure: $55 per 100g

Cost, bulk: $ per 100g

Source: Commercially obtained from the electrolysis of molten Barium Chloride, BaCl2

Isotopes: Barium has 37 isotopes. Naturally occurring barium is a mixture of seven stable isotopes and they are found in the percentages shown:
138Ba (71.7%), 137Ba (11.2%), 136Ba (7.9%), 135Ba (6.6%), 134Ba (2.4%), 130Ba (0.1%) and 132Ba (0.1%).

Of the radioactive isotopes, 133Ba is the longest lived with a half-life of 10.51 years.


1. Mary Elvira Weeks, The Discovery of the Elements. X. The Alkaline Earth Metals and Magnesium and Cadmiun, Journal of Chemical Education., June 1932, p1050.

2. J.W. Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Volume III, 1928, Longmans, Green and Co. Ltd, p619-621

3. Thomas Lamb Phipson, Phosphorescence: or, The emission of light by minerals, plants, and animals., L. Reeve & co., 1862, p12.

4. James L. Marshall and Virginia R. Marshall, Rediscovery of The Elements Phosphoro di Bologna., University of North Texas., p1.

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