Sodium (Na)

Sodium (symbol Na) is the chemical element with atomic number 11: an alkali metal, solid at 0 °C, with an atomic mass of 22.99 u. Discovered in 1807 (Humphry Davy).

Pure sodium is a soft, silvery metal that reacts violently with water. Yet we almost never meet it in that form: it is combined everywhere, above all with chlorine as table salt. In our bodies, sodium ions carry nerve signals. Its orange lamps lit our roads for decades.

Key facts

Atomic number: 11
Symbol: Na
French name: Sodium
Atomic mass: 22.99 u
Molar mass: 22.99 g/mol
Family: Alkali metals
Position: period 3, group 1, s-block
State at 0 °C: Solid
Melting point: 97.8 °C
Boiling point: 882.9 °C
Density: 0.97 g/cm³
Electronegativity (Pauling): 0.93
First ionization energy: 496 kJ/mol
Atomic radius: 180 pm
Electron configuration: [Ne] 3s¹
Abundance in Earth's crust: 23,600 ppm (6th most abundant element)
Indicative price: 3 $/kg (order of magnitude)
Radioactive: no
Discovery: 1807, Humphry Davy

Origin of the name

From soda, via the Arabic suda; the symbol Na comes from the Latin natrium.

What does sodium look like?

A silvery-white metal so soft it cuts like cold butter. It tarnishes within seconds in air, which is why it is stored under oil.

Where is sodium found?

About 2.3% of Earth's crust, the sixth most abundant element. The oceans hold nearly 11 g of sodium per liter. The human body contains about 100 g, mostly in the blood and the fluid between cells.

Natural sources

Halite (rock salt)
Albite (feldspar)
Trona
Natron
Seawater

How is sodium produced?

Salt is extracted from rock-salt mines or by evaporating seawater in salt pans: about 280 million tonnes a year. Sodium metal is obtained by electrolysis of molten salt at around 600 °C (Downs cell).

Top producers

China
United States
India
Germany

What is sodium used for?

Table salt and food preservation.
De-icing roads in winter.
Caustic soda and sodium carbonate for the chemical and glass industries.
Sodium-vapor street lamps.
Coolant in some nuclear reactors.
Sodium-ion batteries, an emerging alternative to lithium.

In everyday life

The salt shaker
Baking soda
Orange streetlights along roads
Window and bottle glass
Soap

Role in living things

Essential: together with potassium, it creates the electrical charge difference that lets nerves transmit signals and muscles contract. It also regulates water volume and blood pressure. The kidneys constantly fine-tune its level in the blood.

Hazards of sodium

The metal reacts with water, giving off hydrogen and heat, sometimes explosively. Caustic soda causes severe burns to skin and eyes. Too much salt in the diet contributes to high blood pressure; the WHO recommends less than 5 g of salt a day.

Cosmic origin

Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of sodium

In October 1807, Humphry Davy passed an electric current through molten caustic soda and watched small beads of shiny metal appear. He named it sodium, after soda. The symbol Na comes from the Latin natrium, from natron, a salt the Egyptians used to mummify bodies.

Did you know?

The yellow-orange color of a flame when salt falls into it comes from sodium, which emits at 589 nanometers.
France's Superphénix reactor was cooled by more than 5,000 tonnes of liquid sodium.
The word “salary” is said to come from salt, prized in antiquity, though historians debate the idea that Roman soldiers were paid in salt.

Isotopes of sodium

A single stable isotope, sodium-23. Two radioactive isotopes are handy in the lab: sodium-22, a positron source, and sodium-24, a tracer.

sodium-22: radioactive, half-life 2.6 years. Positron source for calibrating detectors and probing materials.
sodium-23: 100% of natural sodium, stable
sodium-24: radioactive, half-life 15 h. Tracer for finding pipe leaks and studying how fluids flow.

Common compounds

Table salt (NaCl) · Baking soda (NaHCO₃) · Bleach (NaClO) · Caustic soda (NaOH) · Sodium fluoride (NaF)

Related elements

Same family (alkali metals): Lithium (Li), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr).

Same column (group 1): Hydrogen (H), Lithium (Li), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr).