Sodium

Sodium is the chemical element in the periodic table that has the symbol Na (Natrium in Latin) and atomic 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, reacts violently with water and oxidizes in air (which is why pure sodium must be stored in oil).

Contents

1 Notable characteristics

2 Applications

8 Physiology and Na ions

9 References

10 External links

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.

Under extreme pressure, sodium departs from standard rules for changing to a liquid state. Most materials need more thermal energy to melt under pressure than they do at normal atmospheric pressure. This is due to the fact that the molecules are packed closer together and have less room to move.

At a pressure of 30 gigapascals (300,000 times sea level atmospheric pressure), sodium's melting temperature begins to drop. At around 100 gigapascals, sodium will melt at near room temperature.

A possible explanation for the abberant behavior of sodium is that this element has one free electron that is pushed closer to the other 10 electrons when placed under pressure forcing interaction that is not normally present. While under pressure, solid sodium assumes several odd crystal structures suggesting that the liquid might have unusual properties such as superconduction or superfluidity. (Gregoryanz, et al., 2005)

Applications

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.
As a heat transfer fluid in some types of nuclear reactors.

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

History

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 n�tron, a kind of natural salt.

Occurrence

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.

Compounds

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 (Na₂C O₃), baking soda (NaHCO₃), caustic soda (NaOH), Chile saltpeter (NaNO₃), di- and tri-sodium phosphates, sodium thiosulfate (hypo, Na₂S₂O₃ � 5H₂O), and borax (Na₂B₄O₇ � 10H₂O).

Isotopes

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).

Precautions

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 .

References

Los Alamos National Laboratory – Sodium
Gregoryanz, E., et al. (2005). "Melting of dense sodium". Physical Review Letters, In press, .