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Halide

physical science Maturity 11-13 Next article →

A halide is a binary chemical compound. This means it is made of exactly two parts. One part is always a halogen atom. The other part is an element or a radical. This second part must be less electronegative than the halogen. It might also be described as more electropositive.

Atomic & ionic radii halides
Atomic & ionic radii halides

When these elements combine, they form different types of halides. These include fluoride, chloride, bromide, iodide, astatide, or tennesside compounds. Many common salts are actually halides. The word "halite" is used for minerals that contain these halides.

Halides can bond in different ways. Some form ionic halide salts. In these salts, a halide ion carries a negative charge. Common halide anions include fluoride, chloride, bromide, and iodide. These specific ions are often colorless. Other halides form covalent bonds instead. For example, TiF4 and TiCl4 are colorless. However, TiBr4 is orange and TiI4 is brown.

Atomic & ionic radii halides
Atomic & ionic radii halides

Some of these covalent halides are molecular. This allows them to be distilled very easily. The compound TiCl4, TiBr4, and TiI4 are all examples of this. TiF4 is an outlier in this group. It has a polymeric structure. Because of this structure, it has a melting point of 284 °C.

Chemical reactions change how halides behave. In a standard laboratory, halides cannot be reduced. However, they can all undergo oxidation. This process turns them back into their parent halogens. These halogens are diatomic, meaning they exist in pairs. Scientists can observe and isolate certain intermediates during these reactions. This is especially true for iodide. One well-known intermediate is triiodide. Many other related species, such as polyiodides, are also known.

Atomic & ionic radii halides
Atomic & ionic radii halides

Halides also act as conjugate bases. They are related to hydrogen halides, which are all gases. If you perform protonation in an aqueous solution, you produce hydrohalic acids.

Atomic & ionic radii halides
Atomic & ionic radii halides

Another interesting reaction involves silver ions. Salts like NaCl, NaBr, and NaI dissolve very well in water. These create solutions that are colorless. When you add silver nitrate to these solutions, they react quickly. This reaction creates a solid precipitate. A chloride will form a white precipitate. A bromide will form a pale yellow precipitate. An iodide will form a yellow precipitate.

Atomic & ionic radii halides
Atomic & ionic radii halides

Alkyl halides also react with silver. This reaction is slower than the reaction with alkali metal halides. This process is called the Beilstein test.

We use metal halides in many modern technologies. Metal halide lamps are a great example. These are high-intensity discharge lamps used for street lights. They are more energy-efficient than mercury-vapor lamps. They also have better color rendition than orange high-pressure sodium lamps. People often use these lamps in greenhouses. They are also helpful in rainy climates to supplement sunlight.

Atomic & ionic radii halides
Atomic & ionic radii halides

Silver halides play a vital role in photography. They are used in both photographic films and papers. When light hits the film, the silver halides are exposed. During development, these exposed halides are reduced to metallic silver. This process is what forms the final image.

Atomic & ionic radii halides
Atomic & ionic radii halides

Halides also serve practical industrial purposes. They are used in soldering flux. In these cases, a chlorine or bromine equivalent is often used, such as ZnCl.

Finally, halides are important in the field of synthetic organic chemistry. Chemists often incorporate halogens into organohalide compounds. This helps them build complex new molecules. From lighting our streets to capturing images on film, halides are essential to many systems in our world.

Atomic & ionic radii halides
Atomic & ionic radii halides
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