Sodium is an alkali metal that has been known since prehistoric times. It was isolated for the first time in 1807 by Humphry Davy. Sodium is an essential micronutrient for plants and animals and is used in various industries.
Discovery and History
Sodium in the form of salt (sodium chloride, NaCl) and soda (sodium carbonate, Na2CO3) have been known since prehistoric times  The name of element originated from Arabic word ‘suda’ which means headache, as the association of sodium with headache was known in early times. The metal was first isolated in 1807, through the electrolysis of sodium hydroxide by Sir Humphry Davy. In 1809, Ludwig Wilhelm, a German physicist and chemist, proposed the name Natronium for it. Its chemical abbreviation ‘Na’ was published in the system of atomic symbols in 1814 which is derived from its Latin name ‘natrium’ .
|Periodic Table Classification||Group 1
|State at 20C||Solid|
|Electron Configuration||[Ne] 3s1
|Density||0.97 g.cm-3 at 20°C|
|Atomic Mass||22.99 g.mol -1|
|Electronegativity according to Pauling||0.93|
Sodium is the seventh most abundant element and fifth most abundant metal on the earth. The Earth’s crust contains around 2.27 % of sodium . About 1.08×104 milligrams per liter of sodium is estimated to be present in ocean water in the form of brine. It is never found as a pure element due to its high reactivity . Sodium is found in many minerals, including halite (highly soluble), Amphibole (less soluble), zeolite (less soluble), cryolite (insoluble) and feldspar (insoluble). Sodium is also found in the spectra of stars in both atomic and ionic forms, including the Sun, and the interstellar medium..
Sodium has an atomic number of 1 and atomic mass of 22.98. It is placed in group 1 of periodic table as it has a single electron in its outer most shell that it readily donates, creating a positively charged ion, the Na+ cation. At room temperature Sodium is soft, silvery-white metal which can be easily cut with a knife. It is highly reactive. In air it reacts with oxygen forming grayish white sodium oxide, so it is stored in an inert liquid such as kerosene or in nitrogen gas as it does not react with nitrogen. It is lighter than water. It is a good conductor of heat and electricity and exhibits the photoelectric effect i.e. the emission of electrons when exposed to light. Sodium and its compounds give yellow color to the flame which is the basic analytical test for sodium. It burns at a temperature more than 800 °C (1,500 °F) .
It is highly reactive in air and forms sodium hydroxide (NaOH), which is a strong base on reaction with water. In presence of air, sodium hydroxide film absorbs carbon dioxide, and lead to the formation of sodium bicarbonate. Sodium reacts with halogens under certain conditions to produce light. Halogen acids e.g. hydrofluoric and hydrochloric acid react vigorously with sodium forming sodium halides. With strong mineral acids, sodium reacts to form their salts, for example with nitric acid it yields sodium nitrate and with sulfuric acids it forms sodium sulfate. It is relatively less reactive with carbon, but at 625°C it reacts with carbon monoxide forming sodium carbide and sodium carbonate. With liquid ammonia sodium reacts to give blue colored solutions forming sodamide, but the reaction is quite slow. Organic acids also react with sodium to form sodium salts. The precious metals, such as gold, silver, forms alloy with liquid sodium .
Significance and Uses
- Sodium is one of the most essential elements for life, as sodium and potassium keep a definite balance within the cell and are involved in maintaining an electrolyte balance across the cell membranes .
- It helps in the regulation of blood pressure, blood volume, osmotic equilibrium and pH. Around 500mg of sodium is the minimum physiological requirement per day of human body.
- Sodium Chloride is daily used as seasoning and preservative in diet.
In plants, sodium is a micronutrient which helps in metabolism. It is involved in synthesis of chlorophyll, opening and closing of stomata, and helps in uptake of water. Salts of sodium decrease the salinity of soil by replacing calcium and other ions in clay and transform the clay to a sticky mass .
- Significant amounts of sodium are used to produce synthetic detergents, dyes, intermediates of dye and perfumes.
- It is also used in the purification of hydrocarbons and in the polymerization of unsaturated hydrocarbons .
- It is extensively used in metallurgy as a deoxidant and as a reducing agent for the preparation of zirconium, calcium, titanium, and other transition metals.
According to The US Institute of Medicine, the Tolerable Upper Intake Level for sodium is 2.3 grams per day. A decrease in sodium intake would lead to fewer cases of hypertension . Hypertension causes almost 7.6 million premature deaths worldwide every year. The American Heart Association recommends not more than 1.5 g of sodium per day .
Isotopes of Sodium
Twenty isotopes of sodium are identified, but only one, sodium-23 is stable. Two radioactive, cosmogenic isotopes which are the byproduct of cosmic ray spallation are known, Na-22 which has a half-life of 2.6 years and Na-24 with a half-life of 15 hours. All other isotopes have a half-life of less than one minute [10, 11].
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