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 SrBr₂. At room temperature it is a white, odourless, crystalline powder. Strontium bromide imparts a bright red colour in a

flame test A flame test is an analytical procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element's characteristic flame emission spectrum (which may be affected by the presence of chloride io ...

, 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, ...

and also has some pharmaceutical uses.

Preparation

SrBr₂ 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. Preparatio ...

and

hydrobromic acid Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. ...

. :

\mathrm

Alternatively

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. B ...

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 e ...

source. :

\mathrm

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 unders ...

of SrBr₂, 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 achi ...

SrBr₂ 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 crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pattern ...

with a

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

and

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...

''P''4/''n''. This structure is referred to as α-SrBr₂ and is

isostructural Isostructural chemical compounds have similar chemical structures. " Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous ...

with EuBr₂ and USe₂. Around 920 K (650 °C), α-SrBr₂ 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 hig ...

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 ...

to a much less ordered phase, β-SrBr₂, which adopts the cubic

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

structure. The beta phase of strontium bromide has a much higher ionic conductivity of about 1 S cm⁻¹, comparable to that of molten SrBr₂, 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 In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−) = 109.4712206...° ≈ 109.5° when all four substituents are ...

of bromine number 3 File:Strontium-bromide-xtal-Br4-coordination-3D-bs-17-25.png, Tetrahedral coordination geometry of bromine number 4

References

* http://www.webelements.com/ Strontium compounds Bromides Alkaline earth metal halides {{inorganic-compound-stub

Preparation

Structure

See also

References