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Strontium

Chemical element, symbol Sr and atomic number 38 / From Wikipedia, the free encyclopedia

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Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two vertical neighbors in the periodic table, calcium and barium. It occurs naturally mainly in the minerals celestine and strontianite, and is mostly mined from these.

Quick facts: Strontium, Pronunciation, Appearance, Standar...
Strontium, 38Sr
Strontium_destilled_crystals.jpg
Strontium
Pronunciation
Appearancesilvery white metallic; with a pale yellow tint[1]
Standard atomic weight Ar°(Sr)
Strontium in the periodic table
Ca

Sr

Ba
rubidiumstrontiumyttrium
Atomic number (Z)38
Groupgroup 2 (alkaline earth metals)
Periodperiod 5
Block  s-block
Electron configuration[Kr] 5s2
Electrons per shell2, 8, 18, 8, 2[4]
Physical properties
Phase at STPsolid
Melting point1050 K (777 °C, 1431 °F)
Boiling point1650 K (1377 °C, 2511 °F)
Density (at 20° C)2.582 g/cm3[5]
when liquid (at m.p.)2.375 g/cm3
Heat of fusion7.43 kJ/mol
Heat of vaporization141 kJ/mol
Molar heat capacity26.4 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
Oxidation states+1,[6] +2 (a strongly basic oxide)
ElectronegativityPauling scale: 0.95
Ionization energies
  • 1st: 549.5 kJ/mol
  • 2nd: 1064.2 kJ/mol
  • 3rd: 4138 kJ/mol
Atomic radiusempirical: 215 pm
Covalent radius195±10 pm
Van der Waals radius249 pm
Color lines in a spectral range
Spectral lines of strontium
Other properties
Natural occurrenceprimordial
Crystal structure face-centered cubic (fcc) (cF4)
Lattice constant
Face-centered cubic crystal structure for strontium
a = 608.6 pm (at 20 °C)[5]
Thermal expansion22.55×10−6/K (at 20 °C)[5]
Thermal conductivity35.4 W/(m⋅K)
Electrical resistivity132 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic
Molar magnetic susceptibility−92.0×10−6 cm3/mol (298 K)[7]
Young's modulus15.7 GPa
Shear modulus6.03 GPa
Poisson ratio0.28
Mohs hardness1.5
CAS Number7440-24-6
History
Namingafter the mineral strontianite, itself named after Strontian, Scotland
DiscoveryWilliam Cruickshank (1787)
First isolationHumphry Davy (1808)
Isotopes of strontium
Main isotopes[8] Decay
abun­dance half-life (t1/2) mode pro­duct
82Sr synth 25.36 d ε 82Rb
83Sr synth 1.35 d ε 83Rb
β+ 83Rb
γ
84Sr 0.56% stable
85Sr synth 64.84 d ε 85Rb
γ
86Sr 9.86% stable
87Sr 7% stable
88Sr 82.6% stable
89Sr synth 50.52 d β 89Y
90Sr trace 28.90 y β 90Y
Symbol_category_class.svg Category: Strontium
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Both strontium and strontianite are named after Strontian, a village in Scotland near which the mineral was discovered in 1790 by Adair Crawford and William Cruickshank; it was identified as a new element the next year from its crimson-red flame test color. Strontium was first isolated as a metal in 1808 by Humphry Davy using the then newly discovered process of electrolysis. During the 19th century, strontium was mostly used in the production of sugar from sugar beets (see strontian process). At the peak of production of television cathode-ray tubes, as much as 75% of strontium consumption in the United States was used for the faceplate glass.[9] With the replacement of cathode-ray tubes with other display methods, consumption of strontium has dramatically declined.[9]

While natural strontium (which is mostly the isotope strontium-88) is stable, the synthetic strontium-90 is radioactive and is one of the most dangerous components of nuclear fallout, as strontium is absorbed by the body in a similar manner to calcium. Natural stable strontium, on the other hand, is not hazardous to health.

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