The Online Encyclopedia and Dictionary








Name, Symbol, Number sodium, Na, 11
Series alkali metal
Group, Period, Block 1 (IA), 3, s
Density, Hardness 968 kg/m3, 0.5
Appearance silvery white
Atomic properties
Atomic weight 22.989770 u
Atomic radius (calc.) 180 (190) pm
Covalent radius 124 pm
van der Waals radius 227 pm
Electron configuration [Ne]3s1
e- 's per energy level 2, 8, 8, 8, 3
Oxidation states (Oxide) 2 (strong base)
Crystal structure Cubic body centered
Physical properties
State of matter solid (paramagnetic)
Melting point 370.87 K (207.90 F)
Boiling point 1156 K (1621 F)
Molar volume 23.78 cm3/mol
Heat of vaporization 96.96 kJ/mol
Heat of fusion 2.598 kJ/mol
Vapor pressure 14.3 µPa at 1234 K
Speed of sound 3200 m/s at 20 C
Electronegativity 0.93 (Pauling scale)
Specific heat capacity 1230 J/(kgK)
Electrical conductivity 21 MS/m
Thermal conductivity 141 W/(mK)
1st ionization potential 495.8 kJ/mol
2nd ionization potential 4562 kJ/mol
3rd ionization potential 6910.3 kJ/mol
4th ionization potential 9543 kJ/mol
5th ionization potential 13354 kJ/mol
6th ionization potential 16613 kJ/mol
7th ionization potential 20117 kJ/mol
8th ionization potential 25496 kJ/mol
9th ionization potential 28932 kJ/mol
10th ionization potential 141362 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP
22Na {syn.} 2.602 y epsilon 2.842 22Ne
23Na 100% Na is stable with 12 neutrons
SI units & STP are used except where noted.

Sodium is the chemical element in the periodic table that has the symbol Na (Natrium in Latin) and atom number 11. Sodium is a soft, waxy, silvery reactive metal belonging to the alkali metals that is abundant in natural compounds (especially halite). It is highly reactive, burns with a yellow flame, oxidizes in air and reacts violently with water, forcing it to be kept under oil.


Notable characteristics

Like the other alkali metals, sodium is a soft, light-weight, silvery white, reactive element that is never found as a pure element in nature. Sodium floats in water, as well as decomposing it to release hydrogen gas and hydroxide ions. If ground to a fine enough powder, sodium will ignite spontaneously in water. However, it does not normally ignite in air below 388 kelvins.


Sodium in its metallic form is an essential component in the making of esters and in the manufacture of organic compounds. This alkali metal is also a component of sodium chloride (NaCl) which is vital to life. Other uses:

  • In certain alloys to improve their structure,
  • In soap (in combination with fatty acids),
  • To descale (make its surface smooth) metal, and
  • To purify molten metals.
  • In sodium vapor lamps, an efficient means of producing light from electricity.

NaCl, an compound of sodium ions and chloride ions, is an important heat transfer material.


Sodium (English, soda) has long been recognized in compounds, but was not isolated until 1807 by Sir Humphry Davy through the electrolysis of caustic soda. In medieval Europe a compound of sodium with the Latin name of sodanum was used as a headache remedy. Sodium's symbol, Na, comes for the neo-Latin name for a common sodium compound named natrium, which comes from the Greek ntron, a kind of natural salt.


Sodium is relatively abundant in stars and the D spectral lines of this element are among the most prominent in star light. Sodium makes up about 2.6% by weight of the Earth's crust making it the fourth most abundant element overall and the most abundant alkali metal. It is now produced commercially through the electrolysis of completely dry fused sodium chloride. This method is less expensive than the previous method of electrolyzing sodium hydroxide. Metallic sodium cost about 15 to 20 US cents per pound (US$0.30/kg to US$0.45/kg) in 1997 but reagent grade (ACS) sodium cost about US$35 per pound (US$75/kg) in 1990. It is the cheapest of all metals by volume.


Sodium chloride, better known as common salt, is the most common compound of sodium, but sodium occurs in many other minerals, such as amphibole, cryolite, halite, soda niter, zeolite, etc. Sodium compounds are important to the chemical, glass, metal, paper, petroleum, soap, and textile industries. Soap is generally a sodium salt of certain fatty acids.

The sodium compounds that are the most important to industry are common salt (NaCl), soda ash (Na2CO3), baking soda (NaHCO3), caustic soda (NaOH), Chile saltpeter (NaNO3), di- and tri-sodium phosphates, sodium thiosulfate (hypo, Na2S2O3 5H2O), and borax (Na2B4O7 10H2O).


There are thirteen isotopes of sodium that have been recognized. The only stable isotope is Na-23. Sodium has two radioactive cosmogenic isotopes (Na-22, half-life = 2.605 years; Na-24, half-life ≈ 15 hours).


Sodium's powdered form is highly explosive in water and a poison combined and uncombined with many other elements. This metal should be handled carefully at all times. Sodium must be stored either in an inert atmosphere, or under mineral oil.

Physiology and Na ions

Sodium ions play a diverse role in many physiological processes. Excitable cells, for example, rely on the entry of Na+ to cause a depolarization. An example of this is signal transduction in the human central nervous system .


External links

The contents of this article are licensed from under the GNU Free Documentation License. How to see transparent copy