Strontium (Sr)

Stable isotopes of strontium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Sr-84 38  46  83.913426 0.56%  68.70-82.00% Carbonate
Sr-86  38  48  85.909265 9.86%  >96.00% Carbonate
Sr-87 38 49 86.908882 7.00% >90.00% Carbonate
Sr-88 38 50 87.905617 82.58% 99.90% Carbonate

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Sr

Strontium was discovered in 1790 by Adair Crawford. It is named for the village of Strontian in Scotland.

A silvery-white metal when freshly cut, strontium rapidly turns yellow on exposure to air, forming a thin oxide coating. It has a face-centered cubic structure, is malleable and ductile, and is chemically similar to calcium. Soluble in alcohol, ethanol and acids, strontium is also a reactive metal. In its finely-divided form, the metal is pyrophoric and ignites in air to form both the oxide SrO and the peroxide SrO2. Similarly, when heated with chlorine gas or bromine vapor, it burns brightly, forming its halides, SrCl2 or SrBr2. Strontium is also a reducing agent: it reduces oxides and halides of metals at elevated temperatures to metallic form. Spontaneously flammable in powder form, strontium ignites when heated above its melting point. It reacts with water to evolve hydrogen.

Elemental strontium has only minor uses, since most applications also involve calcium and barium. Strontium's alloys are used as “getters” for vacuum tubes. Strontium is incorporated in glass to make picture tubes for color televisions. Its compounds are used in tracer bullets and in fireworks to produce red signal flares. Strontium titanate is a gemstone. The radioactive isotope Strontium-90, with a half-life of 29 years, is a product of nuclear fission and a high-energy beta emitter. This isotope is a lightweight nuclear-electric power source in space vehicles and remote weather stations.

Strontium's radioactive isotopes emit high-energy beta radiation, causing damage — including cancer — to bone marrow and blood-forming organs.

Properties of Strontium

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
Group name Alkaline earth metal 
Period in periodic table
Block in periodic table s-block 
Color Silvery white 
Classification Metallic 
Melting point 777 °C
Boiling point 1384 °C
Vaporization point 1382 °C
Thermal conductivity 35.4 W/(m·K) at 298.2 °K
Electrical resistivity 23.0 µΩ·cm at 20 °C 
Electronegativity 1.0 
Specific heat 0.3 kJ/kg K
Heat of vaporization 137 kJ·mol-1
Heat of fusion 8 kJ·mol-1
Density of liquid 2.38 g/cm3 at 777 °C
Density of solid 2.64 g/cm3 
Electron configuration [Kr]5s
Atomic radius 2.15 Å 
Oxidation state  +2 
Ionic radius Sr2+: 1.26 Å and 1.44 Å (coordination numbers 8 and 12, respectively)

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