Sodium

Sodium (Na) is a chemical element belonging to the alkali metals (Group 1 of the periodic table). Its atomic number is 11. It is a soft metal with a silvery-white colour that can be cut easily with a knife. Like other alkali metals, it has one electron in its outermost shell, which is why it reacts readily with other substances.

Because of its high reactivity, sodium does not occur naturally in pure elemental form. It is found in minerals and their various compounds, notably sodium chloride (common salt), which is extremely abundant in seawater and in salt layers in the earth's crust.

Physical and chemical properties

Sodium is an extremely soft metal—its density is less than that of water, so it floats when placed in water. When it comes into contact with water, it reacts immediately, releasing hydrogen and sodium hydroxide, along with heat. This reaction can be vigorous. It also oxidizes readily in air, causing its surface to become dull. For this reason it is stored in oil or liquid paraffin or in an inert gas.

Important compounds

Sodium chloride (NaCl) is the most common compound, used in food, food preservation, and chemical industry. Sodium hydroxide (NaOH), known as caustic soda, is a strong base used in soap manufacture, papermaking, and cleaning. Sodium carbonate and sodium bicarbonate (baking soda) are employed in baking, cleaning, and the glass industry.

Role in living organisms

Sodium ions (Na⁺) play an essential role in animal and human physiology. They aid in water balance and osmotic regulation, the transmission of nerve signals, and muscle function. The body maintains a precise sodium balance; the kidneys regulate it. Excessive dietary salt intake is associated with elevated blood pressure, while severe sodium deficiency (hyponatremia) is also dangerous.

Production and industrial use

Pure sodium is typically produced by electrolysis of molten sodium chloride. The metal produced is used in various chemical reactions, in the manufacture of other compounds, and in heat transfer systems such as those found in some nuclear reactors, which rely on the heat-transfer capacity of molten sodium.