Sodium Na

Discovery

Sodium compounds were known for thousands of years. Ancient Egyptians gathered natron, a natural mixture of sodium carbonate and bicarbonate, from dry lake beds and used it for cleaning and mummification. Salt was traded, taxed and used to preserve food across the ancient world. Yet chemists could not break these compounds down, and many thought soda was itself an element.

In 1807 the English chemist Humphry Davy used the newly invented voltaic pile, an early battery, to pass a strong current through molten sodium hydroxide. Globules of a shining metal appeared at the negative electrode. He had isolated potassium the same way only days earlier. The two discoveries demonstrated the power of electrolysis to split compounds that resisted all other methods.

Origin of the name

Davy named the metal after soda, the sodium compounds it came from. The symbol Na comes from the Latin natrium, derived from natron, a name used in German-speaking countries and adopted by Berzelius for the symbol.

Main uses

• Chemicals: sodium chloride is the raw material for sodium hydroxide and chlorine, two of the largest-volume industrial chemicals.
• Glass and soaps: sodium carbonate (soda ash) is a key ingredient in glassmaking and detergents.
• Food: salt seasons and preserves food, and sodium bicarbonate is baking soda.
• Lighting: sodium-vapour street lamps give off a characteristic yellow-orange light and were once very common.
• Energy: liquid sodium carries heat in some fast nuclear reactors, and sodium-ion batteries are being developed as a cheaper alternative to lithium-ion.
• De-icing: rock salt keeps roads clear in winter.

Isotopes

Sodium has just one stable isotope, sodium-23. Among the radioactive isotopes, sodium-22 (half-life about 2.6 years) emits positrons and is used as a laboratory positron source and calibration standard. Sodium-24 (half-life about 15 hours) is used as a tracer in industry and medical research. When fast reactors use sodium coolant, some sodium-23 captures neutrons and becomes sodium-24, which is one reason the coolant is carefully shielded.

In everyday life

Sodium ions help control fluid balance and allow nerve cells to fire by moving across cell membranes. Most people eat far more sodium than they need, mainly in processed foods, and high intake is linked to high blood pressure. The World Health Organization recommends that adults consume less than 2 grams of sodium a day, roughly 5 grams of salt.

The metal itself reacts violently with water, releasing hydrogen that can ignite, so it is stored under oil.