Sodium – facts and properties
- Symbol
- Na
- Atomic number
- 11
- Atomic mass
- 22.99 u
- Period
- 3
- Group
- 1
- Category
- alkali metal
- Electron configuration
- [Ne] 3s¹
- Electronegativity
- 0.93
- Atomic radius
- 190 pm
- Valence electrons
- 1
- State at standard conditions
- solid
- Melting point
- 97.8 °C
- Boiling point
- 883 °C
- Density
- 0.97 g/cm³
- Discovered
- 1807
Sodium is a soft, silvery alkali metal with atomic number 11. It is so reactive that it never occurs as a free metal in nature, yet its compounds are everywhere, from seawater to rock salt to the fluids in your body. It is worth keeping the element and its compounds apart. Table salt is sodium chloride, a stable compound of sodium ions and chloride ions, and it behaves nothing like the metal that fizzes violently on contact with water.
Position in the periodic table
Occurrence and extraction
Sodium is one of the most common elements in the Earth's crust. It is bound in feldspars such as albite, in clay minerals, and in thick beds of rock salt left behind when ancient seas evaporated. In seawater, sodium ions and chloride ions make up most of the dissolved salt. Because a sodium atom gives up its outer electron so readily, the element is only ever found as an ion in compounds.
The metal was first isolated in 1807 by Humphry Davy in London. He passed an electric current through molten caustic soda, which is sodium hydroxide, and saw small metallic globules appear at the cathode. Electrolysis is still the way sodium is made today. In the Downs process, molten sodium chloride, mixed with calcium chloride to lower its melting temperature, is electrolysed between a graphite anode and an iron cathode. Liquid sodium collects at the cathode, while chlorine gas forms at the anode as a valuable by-product. The metal is then handled under an inert atmosphere or oil. The English name comes from soda, while the symbol Na comes from the Latin natrium.
Properties and reactions
Sodium has the electron configuration [Ne] 3s¹, with a single valence electron in its third shell. It sits in period 3 and group 1 among the alkali metals and has a low electronegativity of 0.93. Losing that one electron gives the sodium ion the same stable arrangement as the noble gas neon, so sodium almost always has an oxidation state of plus one in its compounds.
The metal is soft enough to cut with a knife. A freshly cut surface shines like silver but turns dull grey within moments as a film of oxide and hydroxide forms. With a density of 0.97 g/cm³, sodium floats on water, and it melts at only 97.8 °C; the boiling point is 883 °C. Its reaction with water is violent: the products are hydrogen gas and sodium hydroxide solution, which is a strong alkali. The heat released melts the metal and can ignite the hydrogen, and larger pieces react explosively. For this reason sodium is stored under paraffin oil or kerosene, which keeps out both moisture and air. Sodium burns in chlorine to form sodium chloride. Its compounds colour a flame an intense yellow-orange, a test sensitive enough to reveal tiny traces.
Uses in everyday life and technology
Metallic sodium is mainly an industrial chemical. As a powerful reducing agent it is used to produce potassium, sodium hydride and a range of organic compounds. Liquid sodium transfers heat extremely well and serves as the coolant in some fast-neutron nuclear reactors. Sodium-sulfur batteries, which run with molten sodium at high temperature, store electricity for power grids. Sodium vapour lamps once gave many roads and tunnels their characteristic yellow-orange light, though LEDs are steadily replacing them.
In daily life you almost always meet sodium compounds rather than the metal. Common salt seasons and preserves food and keeps winter roads free of ice. Sodium bicarbonate, also called baking soda, makes cakes rise, and sodium carbonate, or washing soda, is a key raw material for glass. Sodium hydroxide is used to make soap and paper and to clear blocked drains. Sodium-ion batteries, built from sodium compounds, are entering the market as a cheaper alternative to lithium-ion cells. In the body, sodium ions control fluid balance and help to carry nerve signals.
Molecules containing this element
- Sodium chloride NaCl
- Sodium fluoride NaF
- Sodium iodide NaI
Quick question
How many valence electrons does neutral sodium (Na) have?
FAQ
Is sodium the same as salt?
No. Sodium is a reactive metal that reacts violently with water and would burn the skin. Table salt is sodium chloride, a compound in which each sodium atom has already given up its outer electron to chlorine. When food labels mention sodium, they mean sodium ions, mostly from salt.
Why does sodium react so violently with water?
Sodium loses its single valence electron very easily. Water molecules accept it, releasing hydrogen gas and leaving hydroxide ions, so the water turns into sodium hydroxide solution. The reaction gives off a lot of heat, which melts the sodium and can set the hydrogen alight.
Why is sodium stored in oil?
Paraffin oil and kerosene do not react with sodium and shield it from the oxygen and moisture in air. Without that protection the metal would tarnish quickly, and any contact with water could release flammable hydrogen.