|Name: sodium||Group number: 1|
|Symbol: Na||Group name: Alkali metal|
|Atomic number: 11||Period number: 3|
|Atomic weight: 22.989770 (2)||Block: s-block|
|CAS Registry ID: 7440-23-5||Voice: |
|Standard state: solid at 298 K||Colour: silvery white|
|Classification: Metallic||Availability: |
Nearing Zero cartoon included by kind permission of Nick Kim.
IsolationHere is a brief summary of the isolation of sodium.
Sodium would not normally be made in the laboratory as it is so readily available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative sodium ion Na+.
Sodium is present as salt (sodium chloride, NaCl) in huge quantities in underground deposits (salt mines) and seawater and other natural waters. It is easily recovered as a solid by drying.
Sodium chloride has a high melting point (> 800°C) meaning that it sould be expensive to melt it in order to carry out the electrolysis. However a mixture of NaCl (40%) and calcium chloride, CaCl2 (60%) melts at about 580°C and so much less energy and so expense is required for the electrolysis.
cathode: Na+(l) + e- Na (l)
anode: Cl-(l) 1/2Cl2 (g) + e-
The electrolysis is carried out as a melt in a "Downs cell". In practice, the electrolysis process produces calcium metal as well but this is solidified in a collection pipe and returned back to the melt.