Sodium

About Sodium

Sodium is a soft alkali metal you can cut with a butter knife — and one that has to live under mineral oil or argon, because that lone 3s¹ electron is so weakly held that contact with moist air ignites it. Drop a piece into water and you get the textbook reaction: 2Na + 2H₂O → 2NaOH + H₂, with the hydrogen often catching the violet-yellow flame from the 589 nm Na D-line. As Na⁺ in solution, the chemistry calms down completely: it's the dominant cation in extracellular fluid at roughly 140 mmol/L, the counter-ion the Na⁺/K⁺ ATPase pumps against gradient to fire every action potential in your nervous system. Industrially, sodium drives the chlor-alkali industry — electrolysis of brine yields NaOH, Cl₂, and H₂ in roughly 80 million tonnes of NaOH a year, which then becomes soap, paper pulp, alumina (Bayer process), and the pH adjuster in half the chemical plants on Earth. The Solvay process turns brine and limestone into Na₂CO₃ for glassmaking. Liquid sodium is used as a primary coolant in fast breeder reactors because of its excellent heat capacity and low neutron absorption. The symbol Na comes from natrium, from Egyptian natron — the Wadi El Natrun deposit ancient Egyptians used to dehydrate mummies.