Strontium bromide is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with a formula SrBr
2. At room temperature it is a white, odourless, crystalline powder. Strontium bromide imparts a bright red colour in a
flame test, showing the presence of strontium ions. It is used in
flares
A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, o ...
and also has some pharmaceutical uses.
Preparation
SrBr
2 can be prepared from
strontium hydroxide
Strontium hydroxide, Sr(OH)2, is a caustic alkali composed of one strontium ion and two hydroxide ions. It is synthesized by combining a strontium salt with a strong base. Sr(OH)2 exists in anhydrous, monohydrate, or octahydrate form.
Prepar ...
and
hydrobromic acid.
:
Alternatively
strontium carbonate can also be used as
strontium
Strontium is the chemical element with the 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 ex ...
source.
:
These reactions give
hexahydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
of SrBr
2, which decomposes to dihydrate at 89 °C. At 180 °C
anhydrous
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
SrBr
2 is obtained.
[Dale L. Perry, Sidney L. Phillips: ''Handbook of Inorganic Compounds''. CRC Press, 1995, , ().]
Structure
At room temperature, strontium bromide adopts a
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...
with a
tetragonal unit cell and
space group ''P''4/''n''. This structure is referred to as α-SrBr
2 and is
isostructural with
EuBr2 and
USe2. Around 920 K (650 °C), α-SrBr
2 undergoes a
first-order
In mathematics and other formal sciences, first-order or first order most often means either:
* "linear" (a polynomial of degree at most one), as in first-order approximation and other calculus uses, where it is contrasted with "polynomials of high ...
solid-solid
phase transition
In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...
to a much less ordered phase, β-SrBr
2, which adopts the cubic
fluorite structure. The beta phase of strontium bromide has a much higher
ionic conductivity of about 1 S cm
−1, comparable to that of molten SrBr
2, due to extensive disorder in the bromide sublattice.
Strontium bromide melts at 930 K (657 °C).
File:Strontium-bromide-xtal-3D-sf.png, Space-filling model
In chemistry, a space-filling model, also known as a ''calotte model'', is a type of three-dimensional (3D) molecular model where the atoms are represented by spheres whose radii are proportional to the radii of the atoms and whose center-to- ...
of the packing of Sr2+ and Br− ions in α-SrBr2
File:Strontium-bromide-xtal-Sr1-coordination-view-2-3D-bs-17-25.png, Distorted square antiprismatic coordination geometry
The term coordination geometry is used in a number of related fields of chemistry and solid state chemistry/physics.
Molecules
The coordination geometry of an atom is the geometrical pattern formed by atoms around the central atom.
Inorganic coo ...
of crystallographically independent strontium atom number 1
File:Strontium-bromide-xtal-Sr2-coordination-view-2-3D-bs-17-25.png, Square antiprismatic coordination geometry of strontium number 2
File:Strontium-bromide-xtal-Br1-coordination-3D-bs-17-25.png, Flattened tetrahedral coordination geometry of bromine number 1
File:Strontium-bromide-xtal-Br2-coordination-3D-bs-17-25.png, Distorted tetrahedral coordination geometry of bromine number 2
File:Strontium-bromide-xtal-Br3-coordination-3D-bs-17-25.png, Tetrahedral coordination geometry of bromine number 3
File:Strontium-bromide-xtal-Br4-coordination-3D-bs-17-25.png, Tetrahedral coordination geometry of bromine number 4
See also
*
Strontium chloride
Strontium chloride (SrCl2) is a salt of strontium and chlorine.
It is a 'typical' salt, forming neutral aqueous solutions. As with all compounds of strontium, this salt emits a bright red colour in flame, and is commonly used in fireworks to that ...
References
* http://www.webelements.com/
Strontium compounds
Bromides
Alkaline earth metal halides
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