Sodium
For sodium in the diet, see Edible salt.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 necessitating storage in an inert environment.
Like the other
alkali metals, sodium metal is a soft, light-weight, silvery white, reactive metal. Owing to its extreme reactivity, in nature it occurs only combined into compounds, and never as a pure elemental metal. Sodium metal floats on
water, and reacts violently with it releasing heat, flammable
hydrogen gas and caustic
sodium hydroxide solution.
Sodium ions are necessary for regulation of blood and body fluids, transmission of nerve impulses, heart activity, and certain metabolic functions. It is widely considered that most people consume more than is needed, in the form of
sodium chloride, or table salt, and that this can have a negative effect on the health.
See Edible salt.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 because 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), the melting temperature of sodium begins to drop. At around 100 gigapascals, sodium will melt near room temperature.
A possible explanation for the aberrant 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 interactions that are 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)
Sodium in its metallic form can be used to refine some reactive metals, such as
zirconium and
potassium, from their 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 metal (make its surface smooth).
*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 and inside the hollow
valves of high-performance
internal combustion engines.
NaCl, a compound of sodium ions and
chloride ions, is an important
heat transfer material.
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 from the
neo-Latin name for a common sodium compound named
natrium, which comes from the
Greek nítron, a kind of natural
salt. As early as 1860
Kirchhoff and
Bunsen noted the sensitivity that a flame test for sodium could have. Stating in
Annalen der Physik und der Chemie in the paper "Chemical Analysis by Observation of Spectra": "In a corner of our 60 cu.m. room farthest away from the apparatus, we exploded 3 mg. of sodium chlorate with milk sugar while observing the nonluminous flame before the slit. After a few minutes, the flame gradually turned yellow and showed a strong sodium line that disappeared only after 10 minutes. From the weight of the sodium salt and the volume of air in the room, we easily calculate that one part by weight of air could not contain more than 1/20 millionth weight of sodium."
 |
The flame test for sodium displays a brilliantly bright yellow emission due to the so called "sodium D-lines" at 588.9950 and 589.5924 nanometers. |
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.
At the end of the 19th century, sodium was chemically prepared by heating
sodium carbonate with
carbon to 1100 °C.:Na
2CO
3 (liquid) + 2 C (solid, coke) → 2 Na (vapor) + 3 CO (gas).
It is now produced commercially through the
electrolysis of liquid
sodium chloride. This is done in a Down's cell in which the NaCl is mixed with
calcium chloride to lower the
melting point below 700 °C. As
calcium is more electropositive than sodium, no calcium will be formed at the cathode. 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.
See also sodium minerals.Sodium chloride or
halite, better known as common salt, is the most common compound of sodium, but sodium occurs in many other
minerals, such as
amphibole,
cryolite,
soda niter and
zeolite. 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 (Na
Cl),
soda ash (Na
2CO3),
baking soda (Na
HCO
3),
caustic soda (NaOH),
Chile saltpeter (Na
NO
3), di- and tri-sodium phosphates,
sodium thiosulfate (hypo, Na
2S2O
3 · 5H
2O), and
borax (Na
2B4O
7 · 10H
2O).
See also sodium compounds.There are thirteen
isotopes of sodium that have been recognized. The only stable isotope is
23Na. Sodium has two
radioactive cosmogenic isotopes (
22Na,
half-life = 2.605 years; and
24Na, half-life ≈ 15 hours).
Acute neutron radiation exposure (e.g., from a nuclear
criticality accident) converts some of the stable
23Na in human blood plasma to
24Na. By measuring the concentration of this isotope, the neutron radiation dosage to the victim can be computed.
Sodium's metallic form is highly explosive in water and is a poison when uncombined with other elements. The powdered form may combust spontaneously in air or oxygen. This metal should be handled carefully at all times. Sodium must be stored either in an inert
atmosphere, or under a liquid hydrocarbon such as mineral oil or
kerosene.
Sodium ions play a diverse and important 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.
Some potent
neurotoxins, such as
batrachotoxin, increase the sodium ion permeability of the
cell membranes in nerves and muscles, causing a massive and irreversible
depolarization of the membranes, with potentially fatal consequences.
*
Los Alamos National Laboratory " Sodium*Rebecca J. Donatelle. Health, The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.
*
:Category:Sodium compounds*
:Category:Alkali metals*
WebElements.com " Sodium*
The Wooden Periodic Table Table's Entry on Sodium*
Dietary Sodium
