Contact explosive

A contact explosive is a chemical substance that explodes violently when it is exposed to a relatively small amount of energy (friction, pressure, sound, light). Though different substances have varying amounts of energy sensitivity, they are all much more sensitive relative to other explosives. Contact explosives are a part of a group of explosives called primary explosives which are also very sensitive to stimuli but not to the degree of contact explosives. The extreme sensitivity of contact explosives is due to either its composition, bonds, or structure.

These are some common contact explosives.

Explosives that are nitrogen-based are incredibly volatile due to the stability of nitrogen in its diatomic state, N₂. Most organic explosives are explosive because they contain nitrogen. They are defined as nitro compounds.

Since nitrogen wants to escape the unstable bonds it has in a big compound so that it can form its highly stable N₂ form, it makes the compound sensitive to exploding. The presence of nitrogen in these explosives also makes them much more powerful. The triple bond that holds N₂ together has an incredible amount of bond energy that when it forms it releases the nitrogen gas at high energies over a short period of time thus creating a huge explosion.

Some contact explosives contain an oxidizer and a fuel in their composition. Chemicals like gasoline, a fuel, burn instead of explode because they must come into contact with oxygen in the combustion reaction. However, if the compound already contains both the oxidant and fuel, it produces a much faster and violent reaction.

The structures and bonds that make up a contact explosive contribute to its instability. Covalent compounds that have a large unequal sharing of electrons have the capability to fall apart very easily and explosively. Nitrogen triiodide is a perfect example of this property. The three huge iodine molecules try to attach themselves to one small nitrogen ion, which means that the atoms are holding on to each other through a very weak bond. The weak bond between each atom is like a thread just waiting to break. Therefore, any small amount of applied energy cuts this thread and releases the large amount of energy that was needed to keep it intact.

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