ChemSphere
11Na22.99

Sodium

Alkali metal · Period 3 · Group 1 · s-block

A metal soft as butter that explodes in water

Atomic mass
22.99 u
State at 25 °C
Solid
Electronegativity
0.93
Melting point
97.8 °C
Boiling point
882.9 °C
Configuration
[Ne] 3s1
Building atom…
11 protons 12 neutrons 11 electrons

Sodium, explained

Overview

Sodium has a single 3s electron outside a neon-like core ([Ne]3s1). That electron is far from the nucleus and shielded by ten inner electrons, so it is removed with little energy (496 kJ/mol), and sodium is a powerful reducing agent that reacts with water, oxygen and halogens. The resulting Na+ ion has the same stable electron arrangement as neon. The metal is soft enough to cut with a knife, has a density of 0.97 g/cm3 so it floats on water, and melts at only 97.8 °C.

Sodium is far too reactive to occur free in nature, but its compounds are everywhere: seawater is about 3.5% dissolved salts, mostly sodium chloride. The metal is produced in Downs cells by electrolysing molten NaCl mixed with calcium chloride to lower the melting point. Heated sodium vapour emits intense yellow light at 589 nm, used in street lamps. In the body, nerve cells rely on the sodium-potassium pump, which moves three Na+ ions out for every two K+ ions in, creating the voltage that carries nerve impulses.

Discovery

In October 1807 Humphry Davy, at the Royal Institution in London, passed an electric current from a large voltaic battery through molten sodium hydroxide and obtained small globules of a new metal, a few days after isolating potassium the same way. He named it sodium after soda, the common name of its compounds. The symbol Na comes from the Latin natrium, derived from natron, a natural sodium carbonate mineral used in ancient Egypt for mummification.

Where it’s found
Sodium is the sixth most abundant element in Earth's crust (about 2.3%), found in rock salt, seawater and many silicate minerals; the metal is made by electrolysis of molten sodium chloride.
What it’s used for
  • Table and road salt
  • Street lighting
  • Sodium hydroxide production
  • Baking soda
  • Reactor coolant
  • Titanium production
In living things
Sodium ions are essential electrolytes that control fluid balance, blood pressure and the electrical signals of nerves and muscles. Too much dietary salt is linked to high blood pressure.
Safety
Sodium metal reacts violently with water, producing hydrogen that can ignite and corrosive sodium hydroxide; it is stored under mineral oil. Sodium fires must be smothered with dry powder, never water.

How it compares

Where Sodium sits among all 118 elements on the trends that shape the table.

  • Electronegativity0.93Pauling

    #94 of 100 elements with data

  • Ionization energy496kJ/mol

    #99 of 104 elements with data

  • Atomic radius180pm

    #17 of 95 elements with data

  • Electron affinity52.9kJ/mol

    #50 of 109 elements with data

  • Density0.968g/cm³

    #101 of 114 elements with data

  • Melting point371K

    #89 of 110 elements with data

Density
0.968 g/cm³
Atomic radius
180 pm
Covalent radius
155 pm
Molar heat
28.23 J/(mol·K)
Appearance
silvery white metallic
Discovered by
Humphry Davy

Inside the atom

11 electrons arranged in 3 shells: 2 · 8 · 1.

Orbital diagram

1s2 2s2 2p6 3s1 · shorthand [Ne] 3s1

  1. 1s2
  2. 2s2
  3. 2p6
  4. 3s1

Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Sodium bonds.

Ionization energies

Energy to remove each electron in turn, on a log scale. The biggest leap, from electron 1 to 2 (×9.2), is where the next electron has to come from a filled shell much closer to the nucleus.

Signature reactions

The chemistry Sodium is known for.

  1. Redox · Single displacement

    Sodium with water

    Sodium melts into a silvery ball that darts across the water surface, hissing as it releases hydrogen. Larger pieces may ignite the hydrogen with a yellow flame or explode. The solution left behind is strongly alkaline sodium hydroxide.

    2Na(s)+2H2O(l)2NaOH(aq)+H2(g)

    Conditions: room temperature

  2. Redox · Synthesis

    Sodium burning in chlorine

    Hot sodium burns in chlorine with a brilliant yellow flame, producing white clouds of sodium chloride. Each sodium atom transfers its 3s electron to a chlorine atom, forming an ionic lattice. Two dangerous substances combine to make ordinary table salt.

    2Na(s)+Cl2(g)2NaCl(s)

    Conditions: warm sodium in chlorine gas

  3. Redox · Electrolysis

    Downs cell electrolysis

    Molten salt is split by electric current: sodium ions gain electrons at the iron cathode and chloride ions lose them at the graphite anode. Liquid sodium floats to the top and is collected while chlorine gas is piped away. Adding calcium chloride lowers the melting point from 801 °C, saving energy.

    2NaCl(l)2Na(l)+Cl2(g)

    Conditions: electrolysis at about 600 °C with added CaCl2

Watch Sodium react in 3D

Where you’ll meet it

Research

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