A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide (AgBr), chloride (AgCl), iodide (AgI), and two forms of silver fluorides. A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Abundance Owing to their high Reactivity, the halogens are found in the environment only in compounds or as Ions Halide ions and oxoanions Silver bromide (AgBr a soft pale-yellow insoluble salt well known (along with other silver halides for its unusual sensitivity to light. Silver chloride is a Chemical compound with the Chemical formula Ag[[Chlorine Cl]] Silver iodide ( Ag[[Iodine I]] is a Chemical compound used in Photography and as an Antiseptic in medicine As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX. Although most silver halides involve silver atoms with oxidation states of +1 (Ag+), silver halides in which the silver atoms have oxidation states of +2 (Ag2+) are known, of which silver(II) fluoride is the only known stable one. In Chemistry, the oxidation state is an indicator of the degree of Oxidation of an Atom in a Chemical compound. Silver(II fluoride is a Chemical compound with the formula AgF2
In photography, "silver halide" precludes silver fluoride.
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Applications
Light sensitivity
Silver halides are used in photographic film and photographic paper, as well as radiographic film and paper, where silver halide crystals in gelatin are coated on to a film base, glass or paper substrate. This article is mainly concerned with Still photography film For Motion picture film please see Film stock. Photographic paper is paper coated with Light -sensitive chemicals used for making Photographic prints Photographic paper differs from photo papers In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating Gelatin (also gelatine, from French gélatine) is a translucent colourless brittle nearly tasteless solid substance, extracted from the A film base is a transparent substrate which acts as a support medium for the Photosensitive Emulsion that lies atop it The gelatin is a vital part of the emulsion as the protective colloid of appropriate physical and chemical properties. Gelatin may also contain trace elements (such as sulfur) which increase the light sensitivity of the emulsion, although modern practice uses gelatin without such components. Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 An emulsion ( IPA: /ɪˈmʌlʃən/ is a mixture of two Immiscible (unblendable liquids When absorbed by an AgX crystal, photons cause electrons to be promoted to a conduction band (de-localized electron orbital with higher energy than a valence band) which can be attracted by a sensitivity speck, which is a shallow electron trap, which may be a crystalline defect or a cluster of silver sulfide, gold, other trace elements (dopant), or combination thereof, and then combined with an interstitial silver ion to form silver metal speck. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena In the Physics field of Semiconductors and insulators the conduction band is the range of Electron Energy, higher than that of the An atomic orbital is a Mathematical function that describes the wave-like behavior of an electron in an atom In Solids the valence band is the highest range of Electron energies where electrons are normally present at Absolute zero. A sensitivity speck is a place in silver halide crystal where Latent image is preferentially formed A dopant, also called doping agent and dope, is an impurity element added to a crystal or semiconductor lattice in low concentrations in order to alter the optical/electrical Silver bromide and silver chloride may be used separately or combined, depending on the sensitivity and tonal qualities desired in the product. Silver iodide is always combined with silver bromide or silver chloride, except in the case of daguerreotype production where a daguerreotype (one of the oldest photographic processes) is developed with pure red light instead of mercury vapors (a method known as the Bequerelle method, named for the inventor who discovered the phenomenon). The daguerreotype (original French daguerréotype) is an early type of Photograph, developed by Louis Daguerre, in which the image is exposed directly
Silver halides are also used to make some corrective lenses darken when exposed to ultraviolet light (see photochromism). A corrective lens is a lens worn in front of the Eye, mainly used to treat Myopia, Hyperopia, astigmatism, and adjustable focus Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Photochromism is the reversible transformation of a chemical species between two forms by the absorption of electromagnetic radiation where the two forms have different absorption spectra
When a silver halide crystal is exposed to light, a sensitivity speck on the surface of the crystal is turned into a small speck of metallic silver (these comprise the invisible or latent image). A sensitivity speck is a place in silver halide crystal where Latent image is preferentially formed A latent image on Photographic film is an invisible image produced by the exposure of the film to Light. If the speck of silver contains approximately four or more atoms, it is rendered developable - meaning that it can undergo development which turns the entire crystal into metallic silver. Photographic processing is the Industrial process by which conventional Photographic film is treated after Photographic exposure in order to produce the Areas of the emulsion receiving larger amounts of light (reflected from a subject being photographed, for example) undergo the greatest development and therefore results in the highest optical density.
Chemistry
Silver halides, except for silver fluoride, are extremely insoluble in water. Silver nitrate can be used to precipitate halides; this application is useful in quantitative analysis of halides. Silver nitrate also known as lunar caustic is a soluble Chemical compound with Chemical formula Ag[[Nitrogen N]] O 3 A halide is a Binary compound, of which one part is a Halogen Atom and the other part is an element or radical that is less The precipitation of silver halides via silver nitrate is also useful for abstracting halide leaving groups. A leaving group is an Atom or group of atoms that detaches from a chemical substance
However, close attention is necessary for other compounds in the test solution. Some compounds can considerably increase or decrease the solubility of AgX. Examples of compounds that increase the solubility include: cyanide, thiocyanate, thiosulfate, thiourea, amines, ammonia, sulfite, thioether, crown ether. Examples of compounds that reduces the solubility include many organic thiols and nitrogen compounds that do not possess solubilizing group other than mercapto group or the nitrogen site, such as mercaptooxazoles, mercaptotetrazoles, especially 1-phenyl-5-mercaptotetrazole, benzimidazoles, especially 2-mercaptobenzimidazole, benzotriazole, and these compounds further substituted by hydrophobic groups. Compounds such as thiocyanate and thiosulfate enhance solubility when they are present in a sufficiently large quantity, due to formation of highly soluble complex ions, but they also significantly depress solubility when present in a very small quantity, due to formation of sparingly soluble complex ions.
References
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