Sodium: the essentials
Sodium is a Group 1 element (or IA in older labelling styles). Group 1 elements are often referred to as the "alkali metals". The chemistry of sodium is dominated by the +1 ion Na+. Sodium salts impart a characteristic orange/yellow colour to flames and orange street lighting is orange because of the presence of sodium in the lamp.
Soap is generally a sodium salt of fatty acids. The importance of common salt to animal nutrition has been recognized since prehistoric times. The most common compound is sodium chloride, (table salt).
The picture above shows the colour arising from adding common salt (NaCl) to a burning mixture of potassium chlorate and sucrose.
The chemistry of sodium is dominated by electron loss to form Na+. Cartoon by Nick D Kim ([Science and Ink], used by permission).
Sodium: historical information
Until the 18th century no distinction was made between potassium and sodium. This was because early chemists did not recognise that "vegetable alkali" (K2CO3, potassium carbonate, coming from deposits in the earth) and "mineral alkali" (Na2CO3, sodium carbonate, derived from wood ashes) are distinct from each other. Eventually a distinction was made.
Sodium was first isolated in 1807 by Sir Humphry Davy, who made it by the electrolysis of very dry molten sodium hydroxide, NaOH. Sodium collected at the cathode. Davy isolated potassium by a similar procedure, also in 1807. Shortly after, Thenard and Gay-Lussac isolated sodium by reducing sodium hydroxide with iron metal at high temperatures.
Sodium is one of the elements which has an alchemical symbol, shown below (alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold).
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Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for sodium is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Sodium around us Read more »
Sodium is a vital element. The human diet must contain a sensible amount of sodium. The sodium cation is the main extracellular (outside cells) cation in animals and is important for nerve function in animals.
The importance of sodium as salt in the diet was recognized well before sodium itself was understood to be an element. This recognition formed the basis of trading of salt deposits lining the Dead Sea in biblical times by the Romans. Prolonged sweating results in sodium ion loss in sweat and it is most important that the sodium ion is replaced through proper diet.
Sodium is never found as the free element ("native") in nature as it is so reactive. Sodium is the sixth most abundant element in the earth's crust at about 2.6 - 3.0%. The most common mineral is rock salt (sodium chloride, NaCl, or halite), but it occurs in many other minerals including sodium borate (borax), sodium carbonate (soda), sodium nitrate (Chile saltpetre). and sodium sulphate (thenardite). In those species, however, it is the anions that are the reason for mining.
Sodium is present in some abundance in the sun and other stars andclearly identifiable by the sodium D lines which are very prominent in the solar spectrum and those of other stars.
|Location||ppb by weight||ppb by atoms||Links|
|Human||1400000 ppb by weight||380000 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 370.87 [97.72 °C (207.9 °F)] K
- Boiling point: 1156 [883 °C (1621 °F)] K
- Enthalpy of fusion: 2.60 kJ mol-1
Crystal structure Read more »
The solid state structure of sodium is: bcc (body-centred cubic).
Sodium: orbital properties Read more »
Sodium atoms have 11 electrons and the shell structure is 2.8.1. The ground state electronic configuration of neutral Sodium is [Ne].3s1 and the term symbol of Sodium is 2S1/2.
- Pauling electronegativity: 0.93 (Pauling units)
- First ionisation energy: 495.8 kJ mol‑1
- Second ionisation energy: 4562 kJ mol‑1
Isolation: 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.
Sodium isotopes Read more »