Strontium Element Facts

The chemical element strontium is classed as an alkali earth metal. It was discovered in 1790 by Adair Crawford.

Data Zone

Classification:	Strontium is an alkali earth metal
Color:	silvery
Atomic weight:	87.62
State:	solid
Melting point:	777 oC, 1050 K
Boiling point:	1380 oC, 1653 K
Electrons:	38
Protons:	38
Neutrons in most abundant isotope:	50
Electron shells:	2,8,18,8,2
Electron configuration:	[Kr] 5s2
Density @ 20oC:	2.6 g/cm3

Show more, including: Heats, Energies, Oxidation,
Reactions, Compounds, Radii, Conductivities

Atomic volume:	33.7 cm3/mol
Structure:	ccp: cubic close-packed
Hardness:	1.5 mohs
Specific heat capacity	0.30 J g-1 K-1
Heat of fusion	8.30 kJ mol-1
Heat of atomization	164 kJ mol-1
Heat of vaporization	144.0 kJ mol-1
1st ionization energy	549.5 kJ mol-1
2nd ionization energy	1064.2 kJ mol-1
3rd ionization energy	4138 kJ mol-1
Electron affinity	5 kJ mol-1
Minimum oxidation number	0
Min. common oxidation no.	0
Maximum oxidation number	2
Max. common oxidation no.	2
Electronegativity (Pauling Scale)	0.95
Polarizability volume	27.6 Å3
Reaction with air	vigorous, ⇒ SrO, Sr2N3
Reaction with 15 M HNO3	vigorous, ⇒ H2, Sr(NO3)2
Reaction with 6 M HCl	vigorous, ⇒ H2, SrCl2
Reaction with 6 M NaOH	vigorous, ⇒ none
Oxide(s)	SrO, SrO2 (strontium peroxide)
Hydride(s)	SrH2
Chloride(s)	SrCl2
Atomic radius	200 pm
Ionic radius (1+ ion)	–
Ionic radius (2+ ion)	132 pm
Ionic radius (3+ ion)	–
Ionic radius (1- ion)	–
Ionic radius (2- ion)	–
Ionic radius (3- ion)	–
Thermal conductivity	35.4 W m-1 K-1
Electrical conductivity	5 x 106 S m-1
Freezing/Melting point:	777 oC, 1050 K

Strontium. Photo by Matthias Zepper.

Discovery of Strontium

Strontium was recognized as a new element in 1790 when Adair Crawford analyzed a mineral sample from a lead mine near Strontian, Scotland. Until then scientists had thought strontium and barium were the same element, and only barium’s existence had been recognized.

The mineral took its name from the Scottish town and was called strontianite (strontium carbonate).

Strontium metal was first isolated in 1808 by Sir Humphry Davy working in London using electrolysis.

Davy had built a very large 600-plate battery, which he used to pass electricity through salts, breaking them down in order to isolate new elements.

He mixed magnesium oxide to a paste with (probably) strontium sulfate. He made a depression in the paste and placed mercury metal there to act as an electrode. Platinum was used as a counter electrode.

When electricity was passed through the paste, a strontium-mercury amalgam formed at the mercury electrode.

Davy removed the mercury from the amalgam by heating it to leave strontium metal. ^(1),(2).

The element was named strontium by Davy after the mineral it was produced from.

Davy discovered or isolated for the first time several alkali and alkali earth metals including potassium, sodium, barium, calcium and magnesium.

Strontium nitrate produces a red color in pyrotechnic displays. Strontium is the source of the red color.

Strontium metal burns in air with a distinctive red flame, forming a mixture of strontium oxide and nitride.

The world’s most accurate atomic clock, based on strontium atoms, would neither gain nor lose a second in more than 200 million years.

Appearance and Characteristics

Harmful effects:

Strontium’s non-radioactive isotopes are considered non-toxic.

Characteristics:

Strontium is a soft, silvery metal. When cut it quickly turns a yellowish color due to the formation of strontium oxide (strontia, SrO). Finely powdered strontium metal is sufficiently reactive to ignite spontaneously in air.

It reacts with water quickly (but not violently like the Group 1 metals) to produce strontium hydroxide and hydrogen gas.

Strontium and its compounds burn with a crimson flame and are used in fireworks.

Strontium’s Periodic Table Neighborhood
Strontium is a Group 2 Alkaline earth metal. It usually exists as a divalent ion, Sr²⁺, in its compounds. Strontium’s chemistry is very similar to that of calcium, which sits above it in Group 2.

Uses of Strontium

Strontium is used for producing glass (cathode ray tubes) for color televisions. It is also used in producing ferrite ceramic magnets and in refining zinc.

The world’s most accurate atomic clock, accurate to one second in 200 million years, has been developed using strontium atoms.

Strontium salts are used in flares and fireworks for a crimson color.

Strontium chloride is used in toothpaste for sensitive teeth.

Strontium oxide is used to improve the quality of pottery glazes.

The isotope ⁹⁰Sr is one of the best long-lived, high-energy beta emitters known. It is used in cancer therapy.

Abundance and Isotopes

Abundance earth’s crust: 370 parts per million by weight, 87 parts per million by moles

Abundance solar system: 50 parts per billion by weight, 0.7 parts per billion by moles

Cost, pure: $100 per 100g

Cost, bulk: $ per 100g

Source: Strontium is never found free in nature. The principal strontium ores are celestine (strontium sulfate, SrSO₄) and strontianite (strontium carbonate, SrCO₃). The main commercial process for strontium metal production is reduction of strontium oxide with aluminum.

Isotopes: Strontium has 28 isotopes whose half-lives are known, with mass numbers 75 to 102. Naturally occurring strontium is a mixture of its four stable isotopes and they are found in the percentages shown: ⁸⁴Sr (0.6%), ⁸⁶Sr (9.9%), ⁸⁷Sr (7.0%) and ⁸⁸Sr (82.6%).

References

1. Mary Elvira Weeks, Discovery of the Elements., Journal of Chemical Education (June 1932) p1046.
2. T. K. Kenyon, Science and Celebrity: Humphry Davy’s Rising Star., Chemical Heritage Magazine, (2008/9 edition).

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