History and Production
The word sodium derived fron English soda but the symbol Na derived from Latin word natrium. It was first isolated by H. Davy in 1807 by electrolysis of caustic soda (NaOH). It is obtained commercially by electrolysis of fused mixture of sodium chloride and calcium chloride. It is used in preparations
of sodamide and esters. An alloy of sodium with potassium is used as heat transfer agent. It is also used in reduction processes to produce titanium, zirconium etc. Sodium compounds are important in a variety of industries such as paper, glass, petroleum, chemical, soap etc.
The metal does not occur free in nature but exists as compounds such as sodium chloride (table salt) and consists of about 2.6% of the earth's crust. Is is soft, bright silvery metal that may react explosively with water. It burns in flame giving a characteristic yellow glow.
Interatomic distance: 371.6 pm
Melting point: 97.80°C
Boiling point: 883°C
Thermal conductivity/Wm-1K-1: 141 (27°C)
Density/kgm-3: 971 (20°C), 928 (m.p.)
Standard Thermodynamic Data (atomic gas)
Enthalpy of formation: 107.5 kJ/mol
Gibbs free energy of formation: 77.0 kJ/mol
Entropy: 153.7 J/mol K
Heat capacity: 20.8 J/mol K
Electronic configuration: [Ne] 3s1
Term symbol: 2S1/2
Electron affinity: 52.8669 kJ/mol Electronegativity (Pauline): 0.93
Ionization energy (first, second, third): 495.846, 4562.45, 6910.28 kJ/mol
Sodium reacts violently with water to give hydrogen and sodium hydrogen. The gas releases may ignite from the heat of reaction.
Sodium also readily reacts with the oxygen in air. For this reason, the metal is usually kept in an inert organic liquid such as paraffin in an air-tight bottle (as shown above).
Sodium is a very reactive metal, forming a wide range of compounds with most inorganic and organic materials. Under certain conditions sodium reacts with halogen vapours to produce light (chemiluminescence).
The reactivity of sodium is powerful enough to reduce most transition metal oxides to the respective metals.
Sodium (and indeed other alkali metals) dissolves in liquid ammonia to form blue solutions and are believed to contain solvated electrons. A slow reaction, which may take several days, eventually produces sodamide (NaNH2) and hydrogen.
It is therefore a powerful reducing agent and is capable to reduce certain organic aromatic compounds that are otherwise difficult or impossible to achieve.
Test for sodium:
(1) Flame test: sodium salts give a persistent golden-yellow color.
(2) Zinc uranyl acetate: a clear solution of this reagent in dilute ethanoic (acetic) acid reacts with a sodium salt forming slowly a yellow crystalline precipitate of sodium zinc uranyl acetate,