Strontium

38 rubidium ← strontium → yttrium Ca ↑ Sr ↓ Ba periodic table
General
Name, Symbol, Number	strontium, Sr, 38
Chemical series	alkaline earth metals
Group, Period, Block	2, 5, s
Appearance	silvery white metallic
Atomic mass	87.62(1) g/mol
Electron configuration	[Kr] 5s2
Electrons per shell	2, 8, 18, 8, 2
Physical properties
Phase	solid
Density (near r.t.)	2.64 g/cm³
Liquid density at m.p.	6.980 g/cm³
Melting point	1050 K (777 °C, 1431 °F)
Boiling point	1655 K (1382 °C, 2520 °F)
Heat of fusion	7.43 kJ/mol
Heat of vaporization	136.9 kJ/mol
Heat capacity	(25 °C) 26.4 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 796 882 990 1139 1345 1646
Atomic properties
Crystal structure	cubic face centered
Oxidation states	2 (strongly basic oxide)
Electronegativity	0.95 (Pauling scale)
Ionization energies (more)	1st: 549.5 kJ/mol
	2nd: 1064.2 kJ/mol
	3rd: 4138 kJ/mol
Atomic radius	200 pm
Atomic radius (calc.)	219 pm
Covalent radius	192 pm
Miscellaneous
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 132 nΩ·m
Thermal conductivity	(300 K) 35.4 W/(m·K)
Thermal expansion	(25 °C) 22.5 µm/(m·K)
Shear modulus	6.1 GPa
Poisson ratio	0.28
Mohs hardness	1.5
CAS registry number	7440-24-6
Notable isotopes
Main article: Isotopes of strontium iso NA half-life DM DE (MeV) DP 82Sr syn 25.36 d ε - 82Rb 83Sr syn 1.35 d ε - 83Rb β+ 1.23 83Rb γ 0.76, 0.36 - 84Sr 0.56% Sr is stable with 46 neutrons 85Sr syn 64.84 d ε - 85Rb γ 0.514D - 86Sr 9.86% Sr is stable with 48 neutrons 87Sr 7.0% Sr is stable with 49 neutrons 88Sr 82.58% Sr is stable with 50 neutrons 89Sr syn 50.52 d ε 1.49 89Y β- 0.909D - 90Sr syn 28.90 y β- 0.546 90Y

Strontium (chemical symbol Sr, atomic number 38) is a soft, silvery white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestite and strontianite.

is a chemical element in the periodic table that has the.

An alkaline earth metal, strontium

The ⁹⁰Sr isotope is present in radioactive fallout and has a half-life of 28.90 years.

Occurrence and isolation

Strontium occurs commonly in nature amd has been estimated to be the fifteenth most abundant element on Earth, averaging 0.034% of all igneous rock. It is found chiefly in the form of minerals celestite (strontium sulfate, SrSO₄) and strontianite (strontium carbonate, SrCO₃). The largest commercially exploited deposits are found in England.

Of the two minerals, celestite occurs in sufficient amounts in sedimentary deposits to make development of mining facilities attractive. It would be more useful to mine strontianite because strontium is used more often in the carbonate form, but there are relatively few known deposits suitable for development.

The metallic form of strontium can be prepared by electrolysis of melted strontium chloride mixed with potassium chloride. The reactions at the electrodes can be represented as follows.

cathode: Sr²⁺ + 2 e^- → Sr

anode: 2 Cl^- → Cl_{2 (g)} + 2 e^-

Alternatively, strontium can be produced by reducing strontium oxide with aluminum in a vacuum, at a temperature at which strontium distills off.

History

In 1790, while examining samples of the barium mineral witherite (barium carbonate, BaCO3), Adair Crawford found the samples to contain a previously unrecorded mineral. The new mineral was named strontianite, after the Scottish village of Strontian. The element strontium itself was discovered in 1798, and metallic strontium was first isolated by Sir Humphry Davy in 1808, by the method of electrolysis.

Strontium was among the radioactive materials released during a fire at a British nuclear reactor at Windscale, Cumbria, in 1957.

Notable characteristics

Given its extreme reactivity to air, this element occurs naturally only in compounds with other elements, as in the minerals strontianite, celestite, etc. It is isolated as a yellowish metal and is somewhat malleable. It is chiefly employed (as strontium nitrate) to add red color to pyrotechnic flames.

Strontium is a bright silvery metal that is softer than calcium and even more reactive in water, which strontium decomposes on contact to produce strontium hydroxide and hydrogen gas. It burns in air to produce both strontium oxide and strontium nitride, but since it does not react with nitrogen below 380°C it will only form the oxide spontaneously at room temperature. It should be kept under kerosene to prevent oxidation; freshly exposed strontium metal rapidly turns a yellowish color with the formation of the oxide. Finely powdered strontium metal will ignite spontaneously in air. Volatile strontium salts impart a beautiful crimson color to flames, and these salts are used in pyrotechnics and in the production of flares.

• Three allotropes of the metal exist, with transition points at 235 and 540 °C.

• Natural strontium is a mixture of four stable isotopes.

• Because strontium has an atomic radius similar to that of calcium, it readily substitutes for Ca in minerals.

Isotopes

In nature, strontium occurs as four stable isotopes: ⁸⁴Sr (0.56%), ⁸⁶Sr (9.86%), ⁸⁷Sr (7.0%), and ⁸⁸Sr (82.58%). Of these, only ⁸⁷Sr is radiogenic; it is produced by decay from the radioactive alkali metal ⁸⁷Rb, which has a half-life of 4.88 × 10¹⁰ years. Thus, there are two sources of ⁸⁷Sr in any material: that formed during primordial nucleosynthesis along with ⁸⁴Sr, ⁸⁶Sr and ⁸⁸Sr, as well as that formed by radioactive decay of ⁸⁷Rb. The ratio ⁸⁷Sr/⁸⁶Sr is the parameter typically reported in geologic investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0.

In addition to the stable isotopes, 16 unstable isotopes of strontium are known. Of greatest importance is ⁹⁰Sr, with a half-life of 28.78 years. It is a byproduct of nuclear fission, which is found in nuclear fallout and presents a health problem since it substitutes for calcium in bone, preventing expulsion from the body. This isotope is one of the best long-lived high-energy beta emitters known, and is used in SNAP (Systems for Nuclear Auxiliary Power) devices. These devices hold promise for use in spacecraft, remote weather stations, navigational buoys, etc, where a lightweight, long-lived, nuclear-electric power source is required. The 1986 Chernobyl nuclear accident contaminated a vast area with ⁹⁰Sr.

Applications

At present the primary use for strontium is in glass for color television cathode ray tubes.

Other commercial uses:

• Production of ferrite magnets and refining zinc.
• Strontium titanate has an extremely high refractive index and an optical dispersion greater than that of diamond, making it useful in a variety of optics applications.
• Strontium titanate has been cut into gemstones, in particular for its use as diamond simulant. However, it is very soft and easily scratches so it is rarely used.
• Strontium is also used in fireworks for red color, it's sometimes used in the theatre, film and television industry for pyrotechnic special effects.
• Strontium aluminate is used as a bright phosphor with long persistence of phosphorescence.
• Strontium chloride is sometimes used in toothpastes for sensitive teeth. One popular brand includes 10% strontium chloride hexahydrate by weight.
• Strontium oxide is sometimes used to improve the quality of some pottery glazes.
• ⁸⁹Sr is the active ingredient in Metastron, a radiopharmaceutical used for bone pain secondary to metastatic prostate cancer. The strontium acts like calcium and is preferentially incorporated into bone at sites of increased osteogenesis. This localization focuses the radiation exposure on the cancerous lesion.
• ⁹⁰Sr has been used as a power source for RTGs. ⁹⁰Sr produces about 0.93 watts of heat per gram (it is lower for the grade of ⁹⁰Sr used in RTGs, which is strontium fluoride). [1] However, ⁹⁰Sr has a lifetime approximately 3 times shorter and has a lower density than ²³⁸Pu, another RTG fuel. The main advantage of ⁹⁰Sr is that it is cheaper than ²³⁸Pu and is found in nuclear waste.
• ⁹⁰Sr is also used in cancer therapy. Its beta emission and long half-life is ideal for superficial radiotherapy.
• Strontium is also commonly used in aerosol paint, such as the Spanish Montana (Montana Hardcore). This is one of the most likely source of exposure to the public.

Precautions

Pure strontium is extremely reactive with air and burns spontaneously. It is therefore considered a fire hazard.

Effects on the human body

The human body absorbs strontium as if it were calcium. These two elements are chemically so similar that the stable forms of strontium do not pose a significant health threat. By contrast, the radioactive isotope ⁹⁰Sr can lead to various bone disorders and diseases, including bone cancer. The "strontium unit" is used in measuring radioactivity from absorbed ⁹⁰Sr.

See also

• Strontium compounds

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory – Strontium. Retrieved August 5, 2005.
• El-Hajj Fuleihan G. (2004). Strontium ranelate — a novel therapy for osteoporosis or a permutation of the same?. New England Journal of Medicine 350 (Jan 29): 504-506. PMID 14749460.
• Meunier PJ, Roux C, Seeman E, Ortolani S, Badurski JE, Spector TD, Cannata J, Balogh A, Lemmel EM, Pors-Nielsen S, Rizzoli R, Genant HK, Reginster JY (2004). The effects of strontium ranelate on the risk of vertebral fracture in women with postmenopausal osteoporosis. New England Journal of Medicine 350 (Jan 29): 459-468. PMID 14749454.

External links

• WebElements.com – Strontium

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