Physical Properties of Sodium Chloride

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Sodium chloride, also known as table salt, is an ionic compound that is the major contributor to the salinity of seawater and the extracellular fluid in multicellular organisms. It is also the main raw material in the industrial manufacturing of such important chemicals as baking soda, sodium carbonate, and hydrochloric acid. It is very soluble in water, but insoluble or poorly soluble in many other polar solvents. It is a white, hard, and brittle solid that conducts electricity when melted.

In the solid state, NaCl is held together by strong coulombic (electrical) attractions between the sodium (Na+) and chlorine (Cl-) ions. In the molten (liquid) state, however, these ions are free to move and this movement is what allows molten salt to conduct electricity.

The diagram below shows a cross-section of the face-centred cubic crystalline structure of NaCl. There are four cations and anions in each unit cell of the crystal.

It is hard to draw these structures without them looking like ions of the same charge are touching each other. However, this isn’t the case. For example, the green chloride ion in the center is resting on 6 cesium ions from the layer below it.

Sodium metal is quite reactive with air in its solid state, and it reacts quickly with water and air in aqueous solution, to form sodium hydroxide and carbon dioxide. It is not particularly reactive with nitrogen, but it does react with halogens, including chlorine and fluorine, to form metallic sodium and sodium chloride. Sodium chloride is very sensitive to shock, heat, and mechanical injury and must be kept away from moist or corrosive materials. It is also unstable in high temperatures and decomposes to produce toxic fumes of hydrochloric acid when exposed to flame or sunlight.