Sodium is an element whose compounds were and are familiar to all, yet which resists extraction as a metal. The word "soda" marks its presence, as in baking soda, bicarbonate of soda, and soda ash. To these add salt (sodium chloride).
Several compounds of sodium are chemically similar to the equivalent potassium substances. At the dawn of modern chemistry, it was unclear that these pairings contained distinct elements. Against this notion, chemist Johann Bohn in 1683 created saltpeter (sodium nitrate) from salt and found it different from common saltpeter (potassium nitrate, potash). This distinction didn't take hold, however, and chemists conducted various similar tests for the next hundred years and more. Finally, in 1807, the great English chemist Humphrey Davy used a battery to apply the technique of electrolysis. He isolated pure sodium and, separately, potassium, to settle the question.
Mining and Production
Because sodium forms many soluble minerals, its greatest abundance is in the salty oceans of the world. It can also be found in salt deposits from former seabeds. Sodium compounds are mined in large quantities annually, either for direct use or as chemical feedstock. Mining in the United States in 2013 included 44 million tonnes of salt and 12 million tonnes of soda ash. Additionally, sodium is a component of some micas, feldspars, and zeolites, which are also mined.
The pure metal is seldom produced, amounting to 100,000 tonnes annually. Electrolysis of molten salt is the preferred method, after which the reactive metal must be stored carefully away from air.
Properties and Uses
Sodium the metal is a soft silver metal that oxidizes quickly in air. It reacts vigorously with water (right), generating heat, though not so much as potassium or lithium. Sodium burns with a distinctive yellow flame. It conducts electricity well.
Several useful sodium compounds were mentioned above. Another is sodium hydroxide, lye, which is used in making soap. Lye is a strong alkali, the opposite of an acid, and because of this is a starting ingredient for many industrial chemical reactions.
Sodium vapor lamps are used as streetlights. They can be recognized by their yellow light (right). Liquid sodium has been used as a coolant in nuclear reactors.
Sodium is a critical nutrient for humans and animals. In the bloodstream, it regulates blood pressure and water retention, while the sodium/potassium balance at the nerve cells permits the transmission of electrical impulses from cell to cell. Sodium is only a micronutrient for terrestrial plants.