Sodium
[Ne] 3s¹ · 2 · 8 · 1
A soft silvery metal you can cut with a knife and which bursts into flame on water. It never occurs free on Earth, yet its compounds — table salt, soda ash — have been part of human life since antiquity.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
Drag to rotate, scroll to zoom
Atomic properties
- Atomic number
- 11
- Atomic mass
- 22.99 а.е.м.
- Electron configuration
- [Ne] 3s¹
- Electrons per shell
- 2 · 8 · 1
- Block
- s-block
- Group
- Alkali metals
- Period
- 3
- Electronegativity (Pauling)
- 0.93
- Electronegativity (Allen)
- 0.87
- Atomic radius
- 190 pm
- Covalent radius
- 166 pm
- Van der Waals radius
- 227 pm
- Ionisation energy 1
- 495.8 kJ/mol
- Ionisation energy 2
- 4 562 kJ/mol
- Ionisation energy 3
- 6 910.3 kJ/mol
- Electron affinity
- 52.8 kJ/mol
- Common oxidation states
- +1
- Oxidation states
- -1, +1
Physical properties
- State at 25 °C
- solid
- Density
- 0.968 g/cm³
- Melting point
- 370.94 K · 97.8 °C
- Boiling point
- 1 156.09 K · 882.9 °C
- Speed of sound
- 3 200 m/s
Thermal properties
- Heat of fusion
- 2.6 kJ/mol
- Heat of vaporisation
- 97.42 kJ/mol
- Specific heat capacity
- 1.228 J/(g·K)
- Thermal conductivity
- 142 W/(m·K)
Mechanical properties
- Young's modulus
- 10 GPa
- Shear modulus
- 3.3 GPa
- Bulk modulus
- 6.3 GPa
- Poisson ratio
- no data
- Mohs hardness
- 0.5
- Brinell hardness
- 0.69 MPa
Electrical and magnetic properties
- Electrical resistivity
- 47.7 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- body-centred cubic (bcc)
- Lattice constants
- a = 429.06 pm
Abundance
- In the crust
- 23 600 mg/kg
- In the ocean
- 10 800 mg/L
- In the universe
- 20 000 mg/kg
- In the human body
- 1 400 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 22Na | — | 2.6 yr | β+ |
| 23Na | 100 % | stable | — |
Sodium-23 is the only stable isotope. Sodium-22, with a 2.6-year half-life, is used as a positron source.
Discovery
- Year of discovery
- 1807
- Discovered by
- Humphry Davy
- Where
- England
- Origin of the name
- from Latin natrium (natron, soda); hence the symbol Na
History
Humphry Davy isolated sodium in 1807 by electrolysing molten alkali, days after doing the same for potassium. The symbol Na comes from Latin natrium, itself from the Egyptian mineral natron.
Where it occurs
The sixth most abundant element in the crust at 23 600 mg/kg. In the ocean sodium is the dominant cation — it is what makes seawater salty.
How it is produced
By electrolysing molten sodium chloride in a Downs cell, which yields chlorine as well. Rock salt is mined and brines are evaporated.
Role in living things
The sodium ion sets the osmotic pressure of extracellular fluid, and the sodium–potassium pump is what carries a nerve impulse. Running that pump takes about a quarter of a resting body's energy.
Safety
Sodium metal ignites in damp air and explodes in water. Excess dietary salt is an established driver of hypertension.
Uses
- Sodium chloride as feedstock for chlorine, soda ash and caustic soda
- Liquid sodium as coolant in fast-neutron reactors
- High-pressure sodium lamps — the characteristic yellow of street lighting
- A reducing agent in titanium and zirconium metallurgy
Curiosities
- The sodium D line at 589 nm is the one that first identified a terrestrial element in the Sun.
- Sodium is lighter than water, at 0.97 g/cm³.
- Chlorine is poisonous, sodium explodes in water, and their compound is table salt.
- Sodium lamps emit a single colour, so nothing under them can be told apart by hue.