Strontium fluoride, SrF
2, also called strontium difluoride and strontium(II) fluoride, is a
fluoride
Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...
of
strontium
Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it 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 ...
. It is a brittle white crystalline solid. In nature, it appears as the very rare mineral
strontiofluorite.
Preparation
Strontium fluoride is prepared by the action of
hydrofluoric acid on
strontium carbonate
Strontium carbonate (SrCO3) is the carbonate salt of strontium that has the appearance of a white or grey powder. It occurs in nature as the mineral strontianite.
Chemical properties
Strontium carbonate is a white, odorless, tasteless powder ...
.
Structure
The solid adopts the
fluorite structure. In the vapour phase the SrF
2 molecule is non-linear with an F−Sr−F angle of approximately 120°.
This is an exception to
VSEPR theory which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarization of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with the Sr−F bonds.
[Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba Bytheway I, Gillespie RJ, Tang TH, Bader RF Inorganic Chemistry, Vol.34, No.9, 2407-2414, 1995 ]
Properties
It is almost insoluble in water (its
Ksp value is approximately 2.0x10
−10 at 25
degrees Celsius).
It irritates eyes and skin, and is harmful when inhaled or ingested.
Similar to CaF
2 and BaF
2, SrF
2 displays
superionic conductivity at elevated temperatures.
Strontium fluoride is transparent to light in the wavelengths from
vacuum ultraviolet (150
nm) to
infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
(11
μm). Its optical properties are intermediate to
calcium fluoride and
barium fluoride.
Uses
Strontium fluoride is used as an
optical material for a small range of special applications, for example, as an
optical coating
An optical coating is one or more thin-film optics, thin layers of material deposited on an optical component such as a lens (optics), lens, prism (optics), prism or mirror, which alters the way in which the optic reflection (physics), reflects a ...
on lenses and also as a
thermoluminescent dosimeter
A radiation dosimeter is a device that measures the equivalent dose, dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern el ...
crystal.
Another use is as a carrier of
strontium-90
Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.79 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine a ...
radioisotope in
radioisotope thermoelectric generator
A radioisotope thermoelectric generator (RTG, RITEG), or radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the Decay heat, heat released by the decay of a suitable radioactive material i ...
s.
References
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Fluorides
Strontium compounds
Optical materials
Crystals
Alkaline earth metal halides
Fluorite crystal structure