Strontium (38)

Strontium does not occur as the free element. Strontium is softer than calcium and decomposes water more vigorously. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish color with the formation of the oxide. The finely divided metal ignites spontaneously in air. Volatile strontium salts impart an excellent crimson color to flames, and these salts are used in pyrotechnic...s (fireworks, for example).

The different colors are a result of adding different metal salts to a burning reaction mixture of potassium chlorate and sucrose. The red color originates from strontium sulphate. The orange/yellow color originates from sodium chloride. The green color originates from barium chlorate and the blue color originates from copper (I) chloride. The lilac color that should be evident from the potassium chlorate is washed out by the other colors, all of which are more intense (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard assessment). Improperly done, this reaction is dangerous!

The picture above shows the color arising from adding strontium sulphate salt (SrSO4) to a burning mixture of potassium chlorate and sucrose. Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment (leave it to the professionals!).

Strontium-90 (90Sr) has a half-life of 28 years. It is a product of nuclear fallout and presents a major health problem. Strontium titanate is an interesting optical material as it has an extremely high refractive index and an optical dispersion greater than that of diamond. It has been used as a gemstone, but it is very soft.

•Name: Strontium
•Symbol: Sr
•Atomic number: 38
•Atomic weight: 87.62
•Standard state: solid at 298 K
•CAS Registry ID: 7440-24-6
•Group in periodic table: 2
•Group name: Alkaline earth metal
•Period in periodic table: 5
•Block in periodic table: s-block
•Color: silvery white
•Classification: Metallic

Historical information

Strontium was discovered by Adair Crawford at 1790 in Scotland. Origin of name is after the village of "Strontian" in Scotland. Adair Crawford in 1790 recognized a new mineral (strontianite) in samples of witherite (a mineral consisting of barium carbonate, BaCO3) from Scotland. It was some time before it was recognized that strontianite contained a new element. Strontianite is now known to consist of strontium carbonate, SrCO3. The element itself was not isolated for a number of years after this when strontium metal was isolated by Davy by electrolysis of a mixture containing strontium chloride and mercuric oxide in 1808.

Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for strontium is a circle with dashes at the N, E, S, W quarters (kind of like a sighting reticle on guns/rifles)

Physical properties

•Melting point: 1050 [or 777 °C (1431 °F)] K
•Boiling point: 1655 [or 1382 °C (2520 °F)] K
•Density of solid: 2630 kg m-3

Orbital properties

•Ground state electron configuration: [Kr].5s2
•Shell structure: 2.8.18.8.2
•Term symbol: 1S0

Isolation

Strontium metal is available commercially and there is no need to make it in the laboratory. Commercially it is made on small scale by the electrolysis of molten strontium chloride, SrCl2.

Cathode: Sr2+(l) + 2e- → Sr                                         Anode: Cl-(l) → 1/2Cl2 (g) + e-

Strontium metal can also be isolated from the reduction of strontium oxide, SrO, with aluminum.

6SrO + 2Al → 3Sr + Sr3Al2O6