Strontium fluoride
Encyclopedia
Strontium fluoride, SrF2, also called strontium difluoride and strontium(II) fluoride, is a fluoride
of strontium
. It is a stable brittle white crystalline solid with melting point of 1477°C and boiling point 2460°C.
with fluorine
gas, or by action of hydrofluoric acid
on strontium carbonate
.
structure. In the vapour phase the SrF2 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 polarisation of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with the Sr-F bonds.
.
It irritates eyes and skin, and is harmful when inhaled or ingested.
Similar to CaF2 and BaF2, SrF2 displays superionic conductivity at elevated temperatures.
Strontium fluoride is transparent to light in the wavelengths from vacuum ultraviolet (150 nm
) to infrared
(11 µm
). Its optical properties are intermediate to calcium fluoride
and barium fluoride
.
on lenses and also as a thermoluminescent
dosimeter
crystal.
Another use is as a carrier of strontium-90
radioisotope in radioisotope thermoelectric generator
s.
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
of strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
. It is a stable brittle white crystalline solid with melting point of 1477°C and boiling point 2460°C.
Preparation
Strontium fluoride is prepared by reaction of strontium chlorideStrontium chloride
Strontium chloride is a salt of strontium and chloride. It is a typical salt, forming neutral aqueous solutions. Like all compounds of Sr, this salt emits a bright red colour in a flame; in fact is used as a source of redness in fireworks...
with fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
gas, or by action of hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
on strontium carbonate
Strontium carbonate
Strontium carbonate 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 :...
.
Structure
The solid adopts the fluoriteCalcium fluoride
Calcium fluoride is the inorganic compound with the formula CaF2. This ionic compound of calcium and fluorine occurs naturally as the mineral fluorite . It is the source of most of the world's fluorine. This insoluble solid adopts a cubic structure wherein calcium is coordinated to eight fluoride...
structure. In the vapour phase the SrF2 molecule is non-linear with an F-Sr-F angle of approximately 120°. This is an exception to VSEPR theory
VSEPR theory
Valence shell electron pair repulsion theory is a model in chemistry used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion. It is also named Gillespie–Nyholm theory after its two main developers...
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 polarisation of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with the Sr-F bonds.
Properties
It is almost insoluble in water (its Ksp value is approximately 2.0x10-10 at 25 degrees CelsiusCelsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
.
It irritates eyes and skin, and is harmful when inhaled or ingested.
Similar to CaF2 and BaF2, SrF2 displays superionic conductivity at elevated temperatures.
Strontium fluoride is transparent to light in the wavelengths from vacuum ultraviolet (150 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
) to infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
(11 µm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
). Its optical properties are intermediate to calcium fluoride
Calcium fluoride
Calcium fluoride is the inorganic compound with the formula CaF2. This ionic compound of calcium and fluorine occurs naturally as the mineral fluorite . It is the source of most of the world's fluorine. This insoluble solid adopts a cubic structure wherein calcium is coordinated to eight fluoride...
and barium fluoride
Barium fluoride
Barium fluoride is a chemical compound of barium and fluorine. It is a solid which can be a transparent crystal. It occurs in nature as the mineral frankdicksonite.-Structure:...
.
Uses
Strontium fluoride is used as an optical material for a small range of special applications, for example, as an optical coatingOptical coating
An optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and...
on lenses and also as a thermoluminescent
Thermoluminescence
Thermoluminescence is a form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon heating of the material...
dosimeter
Dosimeter
Dosimeters measure an individual's or an object'sexposure to something in the environment — particularly to a hazard inflicting cumulative impact over long periods of time, or over a lifetime...
crystal.
Another use is as a carrier of strontium-90
Strontium-90
Strontium-90 is a radioactive isotope of strontium, with a half-life of 28.8 years.-Radioactivity:Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard...
radioisotope in radioisotope thermoelectric generator
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
s.