Potassium Chloride Crystal Structure

History

• Potassium chloride salt was first discovered in 1807 during Sir Humphrey Davy's experiments into the possibility to separating the constituent elements in a compound using electrolysis. Despite its relatively late discovery, potassium chloride has been in common use by humans for millennia, being a constituent of potash and thereby used in the soap and textile industries.

Metallic Bonding

• Potassium chloride is an ionic metal compound and as such, the elements it contains are subject to metallic bonding. The elements composing the potassium chloride salt form into a rigid crystalline structure of metal ions which are bound together through a mass sharing of electrons, sometimes referred to as an "electron sea."

Shape

• Potassium chloride binds in a more complex version of the standard face-centered cubic structure whereby each face of the cube contains nine atoms in a three-by-three grid. The atoms are structured so one atom of potassium binds to a neighboring chlorine along one axis, which then binds to another potassium and the cycle repeats. This face-centered cubic with a two-atom base structure is common in ionic metal compounds.

Size

• Because of its cubic lattice structure, the lattice constants of potassium chloride are all equal at 630 picometers (0.0000000248 inches). A lattice constant is the distance over which a single group of atoms forming a unit or block within the lattice will repeat. The strength of the potassium chloride crystal structure is sufficient to allow these units to repeat thousands of times, creating large crystals.

Effects

• The ionic metal crystal structure of potassium chloride allows the crystal to conduct electricity. It is far less efficient at conducting heat however, and has a thermal conductivity rating almost 20 percent that of water. Because of the ionic structure of this salt, potassium chloride will dissolve readily in water.