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Reactive Group Datasheet
Flammability
Inorganic fluorides are generally not flammable.
Reactivity
Soluble inorganic fluorides can react slowly with water to form hydrofluoric acid. Unlike other hydrogen halide acids, the anion (fluoride ion) is quite reactive, and can form fairly insoluble salts with alkaline earth metals such as calcium and magnesium. Fluoride also is significantly reactive with silicon-containing compounds, and because of this hydrofluoric acid is used to etch glass.
Toxicity
Since the fluoride ion can react with calcium and magnesium, it can be dangerous to living organisms. The anhydrous gaseous form of hydrofluoric acid, called hydrogen fluoride, is a very dangerous and toxic gas that reacts immediately upon contact with eyes, skin, and lungs. Direct skin exposure to the aqueous solution (hydrofluoric acid) can cause severe chemical burns and local nerve damage due to the interference of fluoride with the calcium and magnesium needed for proper nerve function.
Very low level exposures to fluoride ion can actually be beneficial to humans, since the replacement of hydroxide with fluoride in the teeth makes the teeth harder and more resistant to cavities than they would be otherwise. In slightly higher doses, fluoride exposure can cause a condition called fluorosis, in which teeth and bones become more brittle and may break more easily.
Other Characteristics
The compounds in this group are water-soluble fluoride salts which can react with trace amounts of water to form the dangerous acid hydrogen fluoride, or hydrofluoric acid. They provide a ready source of fluoride ions. Although hydrofluoric acid is technically a weak acid, it can undergo additional reactions that other hydrogen halide acids and other weak acids do not participate in, due to the unusual reactivity of the fluoride ion. Some reactions specific to hydrofluoric acid include reactions with calcium-containing compounds, which makes hydrofluoric acid especially toxic to organisms with bones, and reactions with silicon-containing compounds, which means that hydrofluoric acid is one of the few compounds that can etch glass.
Examples
Hydrogen fluoride, potassium bifluoride, stannous fluoride.