Sodium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol Na (from Latin ''natrium'') and
atomic number 11. It is a soft, silvery-white, highly reactive
metal. Sodium is an
alkali metal, being in
group 1 Group 1 may refer to:
* Alkali metal, a chemical element classification for Alkali metal
* Group 1 (racing), a historic (until 1981) classification for Touring car racing, applied to standard touring cars. Comparable to modern FIA Group N
* Group On ...
of the periodic table. Its only stable
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...
is
23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the
sixth most abundant element in the Earth's crust and exists in numerous
minerals
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
such as
feldspars,
sodalite, and
halite (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been
leached by the action of water from the
Earth's mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s over eons, and thus sodium and
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
are the most common dissolved elements by weight in the oceans.
Sodium was first isolated by
Humphry Davy in 1807 by the
electrolysis of
sodium hydroxide. Among many other useful sodium compounds,
sodium hydroxide (
lye
A lye is a metal hydroxide traditionally obtained by leaching wood ashes, or a strong alkali which is highly soluble in water producing caustic basic solutions. "Lye" most commonly refers to sodium hydroxide (NaOH), but historically has been u ...
) is used in
soap manufacture, and
sodium chloride (
edible salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantit ...
) is a
de-icing
Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prev ...
agent and a nutrient for animals including humans.
Sodium is an
essential element for all animals and some plants. Sodium ions are the major cation in the
extracellular fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a low ...
(ECF) and as such are the major contributor to the ECF
osmotic pressure and ECF compartment volume. Loss of water from the ECF compartment increases the sodium concentration, a condition called
hypernatremia
Hypernatremia, also spelled hypernatraemia, is a high concentration of sodium in the blood. Early symptoms may include a strong feeling of thirst, weakness, nausea, and loss of appetite. Severe symptoms include confusion, muscle twitching, and b ...
.
Isotonic loss of water and sodium from the ECF compartment decreases the size of that compartment in a condition called ECF
hypovolemia.
By means of the
sodium-potassium pump, living human cells pump three sodium ions out of the cell in exchange for two potassium ions pumped in; comparing ion concentrations across the cell membrane, inside to outside,
potassium measures about 40:1, and sodium, about 1:10. In
nerve cells, the electrical charge across the cell membrane enables transmission of the nerve impulse—an
action potential—when the charge is dissipated; sodium plays a key role in that activity.
Characteristics
Physical
Sodium at
standard temperature and pressure is a soft silvery metal that combines with oxygen in the air and forms grayish white
sodium oxide unless immersed in oil or inert gas, which are the conditions it is usually stored in. Sodium metal can be easily cut with a knife and is a good conductor of electricity and heat because it has only one electron in its valence shell, resulting in weak
metallic bonding
Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be des ...
and free electrons, which carry energy. Due to having low atomic mass and large atomic radius, sodium is third-least dense of all elemental metals and is one of only three metals that can float on water, the other two being lithium and potassium.
[Greenwood and Earnshaw, p. 75]
The melting (98 °C) and boiling (883 °C) points of sodium are lower than those of lithium but higher than those of the heavier alkali metals potassium, rubidium, and caesium, following periodic trends down the group. These properties change dramatically at elevated pressures: at 1.5
Mbar
The bar is a metric unit of pressure, but not part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa (100 kPa), or slightly less than the current average atmospheric pressure on Earth at sea lev ...
, the color changes from silvery metallic to black; at 1.9 Mbar the material becomes transparent with a red color; and at 3 Mbar, sodium is a clear and transparent solid. All of these high-pressure
allotropes are insulators and
electrides.
In a
flame test
A flame test is an analytical procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element's characteristic flame emission spectrum (which may be affected by the presence of chloride io ...
, sodium and its compounds glow yellow because the excited
3s electrons of sodium emit a
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...
when they fall from 3p to 3s; the wavelength of this photon corresponds to the
D line at about 589.3 nm.
Spin-orbit interactions involving the electron in the 3p orbital split the D line into two, at 589.0 and 589.6 nm;
hyperfine structures involving both orbitals cause many more lines.
Isotopes
Twenty isotopes of sodium are known, but only
23Na is stable.
23Na is created in the
carbon-burning process in stars by fusing two
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
atoms together; this requires temperatures above 600 megakelvins and a star of at least three solar masses. Two
radioactive,
cosmogenic
Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an ''in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom ...
isotopes are the byproduct of
cosmic ray spallation
Cosmic ray spallation, also known as the x-process, is a set of naturally occurring nuclear reactions causing nucleosynthesis; it refers to the formation of chemical elements from the impact of cosmic rays on an object. Cosmic rays are highly ener ...
:
22Na has a
half-life of 2.6 years and
24Na, a half-life of 15 hours; all other isotopes have a half-life of less than one minute.
Two
nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited states have ...
s have been discovered, the longer-lived one being
24mNa with a half-life of around 20.2 milliseconds. Acute neutron radiation, as from a nuclear
criticality accident
A criticality accident is an accidental uncontrolled nuclear fission chain reaction. It is sometimes referred to as a critical excursion, critical power excursion, or divergent chain reaction. Any such event involves the unintended accumulation ...
, converts some of the stable
23Na in human blood to
24Na; the neutron radiation dosage of a victim can be calculated by measuring the concentration of
24Na relative to
23Na.
Chemistry
Sodium atoms have 11 electrons, one more than the stable configuration of the
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...
neon. The first and second
ionization energies are 495.8 kJ/mol and 4562 kJ/mol, respectively. As a result, sodium usually forms
ionic compounds involving the Na
+ cation.
Metallic sodium
Metallic sodium is generally less reactive than
potassium and more reactive than
lithium. Sodium metal is highly reducing, with the
standard reduction potential for the Na
+/Na couple being −2.71 volts, though potassium and lithium have even more negative potentials.
The thermal, fluidic, chemical, and nuclear properties of molten sodium metal have caused it to be one of the main coolants of choice for the
fast breeder reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use, by irradiation of a fertile mater ...
. Such nuclear reactors are seen as a crucial step for the production of clean energy.
Salts and oxides
Sodium compounds are of immense commercial importance, being particularly central to industries producing
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
,
paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distrib ...
,
soap
Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
, and
textiles.
The most important sodium compounds are
table salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
(Na
Cl),
soda ash
Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
(Na
2 CO3),
baking soda
Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3� ...
(Na
HCO3),
caustic soda
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
(NaOH),
sodium nitrate (Na
NO3), di- and tri-
sodium phosphates,
sodium thiosulfate (Na
2 S2O3·5H
2O), and
borax (Na
2 B4O
7·10H
2O).
In compounds, sodium is usually
ionically bonded to water and anions and is viewed as a
hard Lewis acid.
Most
soap
Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
s are sodium salts of
fatty acids. Sodium soaps have a higher melting temperature (and seem "harder") than potassium soaps.
Sodium containing mixed oxides are promising catalysts and photocatalysts. Photochemically intercalated sodium ion enhances the photoelectrocatalytic activity of
WO3.
Like all the
alkali metals, sodium reacts
exothermically with water. The reaction produces caustic soda (
sodium hydroxide) and flammable
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas. When burned in air, it forms primarily
sodium peroxide with some
sodium oxide.
[Greenwood and Earnshaw, p. 84]
Aqueous solutions
Sodium tends to form water-soluble compounds, such as
halides
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...
,
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
s,
nitrates,
carboxylates and
carbonates. The main aqueous species are the aquo complexes
2O)''n''">a(H2O)''n''sup>+, where ''n'' = 4–8; with ''n'' = 6 indicated from X-ray diffraction data and computer simulations.
Direct precipitation of sodium salts from aqueous solutions is rare because sodium salts typically have a high affinity for water. An exception is
sodium bismuthate (NaBiO
3). Because of the high solubility of its compounds, sodium salts are usually isolated as solids by evaporation or by precipitation with an organic antisolvent, such as
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
; for example, only 0.35 g/L of sodium chloride will dissolve in ethanol.
Crown ether
In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups (). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., . Impo ...
s, like
15-crown-5, may be used as a
phase-transfer catalyst.
Sodium content of samples is determined by
atomic absorption spectrophotometry or by
potentiometry using ion-selective electrodes.
Electrides and sodides
Like the other alkali metals, sodium dissolves in ammonia and some amines to give deeply colored solutions; evaporation of these solutions leaves a shiny film of metallic sodium. The solutions contain the
coordination complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. ...
(Na(NH
3)
6)
+, with the positive charge counterbalanced by
electrons as anions;
cryptand
In chemistry, cryptands are a family of synthetic, bicyclic and polycyclic, multidentate ligands for a variety of cations. The Nobel Prize for Chemistry in 1987 was given to Donald J. Cram, Jean-Marie Lehn, and Charles J. Pedersen for their ...
s permit the isolation of these complexes as crystalline solids. Sodium forms complexes with crown ethers, cryptands and other ligands.
For example,
15-crown-5 has a high affinity for sodium because the cavity size of 15-crown-5 is 1.7–2.2 Å, which is enough to fit the sodium ion (1.9 Å). Cryptands, like crown ethers and other
ionophore
In chemistry, an ionophore () is a chemical species that reversibly binds ions. Many ionophores are lipid-soluble entities that transport ions across the cell membrane. Ionophores catalyze ion transport across hydrophobic membranes, such as liq ...
s, also have a high affinity for the sodium ion; derivatives of the
alkalide An alkalide is a chemical compound in which alkali metal atoms are anions (negative ions) with a charge or oxidation state of −1. Until the first discovery of alkalides in the 1970s, alkali metals were known to appear in salts only as cations ...
Na
− are obtainable by the addition of cryptands to solutions of sodium in ammonia via
disproportionation.
Organosodium compounds
Many organosodium compounds have been prepared. Because of the high polarity of the C-Na bonds, they behave like sources of
carbanions (salts with organic
anions). Some well-known derivatives include
sodium cyclopentadienide (NaC
5H
5) and trityl sodium ((C
6H
5)
3CNa).
Sodium naphthalene
Sodium naphthalene is an organic salt with the chemical formula Na+. In the research laboratory, it is used as a reductant in the synthesis of organic, organometallic, and inorganic chemistry. It is usually generated in situ. When isolated, it ...
, Na
+ 10H8•">10H8•sup>−, a strong reducing agent, forms upon mixing Na and naphthalene in ethereal solutions.
Intermetallic compounds
Sodium forms alloys with many metals, such as potassium,
calcium,
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
, and the
group 11 and
12 elements. Sodium and potassium form KNa
2 and
NaK. NaK is 40–90% potassium and it is liquid at
ambient temperature. It is an excellent thermal and electrical conductor. Sodium-calcium alloys are by-products of the electrolytic production of sodium from a binary salt mixture of NaCl-CaCl
2 and ternary mixture NaCl-CaCl
2-BaCl
2. Calcium is only partially
miscible with sodium, and the 1-2% of it dissolved in the sodium obtained from said mixtures can be precipitated by cooling to 120 °C and filtering.
In a liquid state, sodium is completely miscible with lead. There are several methods to make sodium-lead alloys. One is to melt them together and another is to deposit sodium electrolytically on molten lead cathodes. NaPb
3, NaPb, Na
9Pb
4, Na
5Pb
2, and Na
15Pb
4 are some of the known sodium-lead alloys. Sodium also forms alloys with
gold (NaAu
2) and
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
(NaAg
2). Group 12 metals (
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
,
cadmium and
mercury) are known to make alloys with sodium. NaZn
13 and NaCd
2 are alloys of zinc and cadmium. Sodium and mercury form NaHg, NaHg
4, NaHg
2, Na
3Hg
2, and Na
3Hg.
History
Because of its importance in human health, salt has long been an important commodity, as shown by the English word ''salary'', which derives from ''salarium'', the wafers of salt sometimes given to Roman soldiers along with their other wages. In medieval Europe, a compound of sodium with the Latin name of ''sodanum'' was used as a
headache remedy. The name sodium is thought to originate from the Arabic ''suda'', meaning headache, as the headache-alleviating properties of
sodium carbonate or soda were well known in early times.
Although sodium, sometimes called ''soda'', had long been recognized in compounds, the metal itself was not isolated until 1807 by
Sir Humphry Davy
Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for the ...
through the
electrolysis of
sodium hydroxide.
In 1809, the German physicist and chemist
Ludwig Wilhelm Gilbert proposed the names ''Natronium'' for Humphry Davy's "sodium" and ''Kalium'' for Davy's "potassium".
The chemical abbreviation for sodium was first published in 1814 by
Jöns Jakob Berzelius in his system of atomic symbols, and is an abbreviation of the element's
New Latin
New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...
name ''natrium'', which refers to the Egyptian ''
natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate ( Na2CO3·10H2O, a kind of soda ash) and around 17% sodium bicarbonate (also called baking soda, NaHCO3) along with small quantities of sodium chloride and sodium sulfate. ...
'',
a natural mineral salt mainly consisting of hydrated sodium carbonate. Natron historically had several important industrial and household uses, later eclipsed by other sodium compounds.
Sodium imparts an intense yellow color to flames. As early as 1860,
Kirchhoff and
Bunsen noted the high sensitivity of a sodium flame test, and stated in
Annalen der Physik und Chemie:
In a corner of our 60 m3 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 while, it glowed a bright 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.
Occurrence
The Earth's crust contains 2.27% sodium, making it the
seventh most abundant element on Earth and the fifth most abundant metal, behind
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
,
calcium, and
magnesium and ahead of potassium.
[Greenwood and Earnshaw, p. 69.] Sodium's estimated oceanic abundance is 10.8 grams per liter.
Because of its high reactivity, it is never found as a pure element. It is found in many minerals, some very soluble, such as
halite and
natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate ( Na2CO3·10H2O, a kind of soda ash) and around 17% sodium bicarbonate (also called baking soda, NaHCO3) along with small quantities of sodium chloride and sodium sulfate. ...
, others much less soluble, such as
amphibole and
zeolite. The insolubility of certain sodium minerals such as
cryolite
Cryolite ( Na3 Al F6, sodium hexafluoroaluminate) is an uncommon mineral identified with the once-large deposit at Ivittuut on the west coast of Greenland, mined commercially until 1987.
History
Cryolite was first described in 1798 by Danish vete ...
and
feldspar arises from their polymeric anions, which in the case of feldspar is a polysilicate.
Astronomical observations
Atomic sodium has a very strong
spectral line in the yellow-orange part of the spectrum (the same line as is used in
sodium-vapour street lights). This appears as an
absorption line in many types of stars, including the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. The line was first studied in 1814 by
Joseph von Fraunhofer during his investigation of the lines in the solar spectrum, now known as the
Fraunhofer lines
In physics and optics, the Fraunhofer lines are a set of spectral absorption lines named after the German physicist Joseph von Fraunhofer (1787–1826). The lines were originally observed as dark features (absorption lines) in the optical spectru ...
. Fraunhofer named it the "D" line, although it is now known to actually be a group of closely spaced lines split by a
fine and
hyperfine structure.
The strength of the D line allows its detection in many other astronomical environments. In stars, it is seen in any whose surfaces are cool enough for sodium to exist in atomic form (rather than ionised). This corresponds to stars of roughly
F-type and cooler. Many other stars appear to have a sodium absorption line, but this is actually caused by gas in the foreground
interstellar medium. The two can be distinguished via high-resolution spectroscopy, because interstellar lines are much narrower than those broadened by
stellar rotation.
Sodium has also been detected in numerous
Solar System
The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
environments, including
Mercury's atmosphere, the
exosphere of the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, and numerous other bodies. Some
comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
s have a
sodium tail, which was first detected in observations of
Comet Hale–Bopp
Comet Hale–Bopp (formally designated C/1995 O1) is a comet that was one of the most widely observed of the 20th century and one of the brightest seen for many decades.
Alan Hale and Thomas Bopp discovered Comet Hale–Bopp separately ...
in 1997.
Sodium has even been detected in the atmospheres of some
extrasolar planet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
s via
transit spectroscopy.
Commercial production
Employed only in rather specialized applications, only about 100,000 tonnes of metallic sodium are produced annually.
Metallic sodium was first produced commercially in the late 19th century
by
carbothermal reduction
Carbothermic reactions involve the reduction of substances, often metal oxides (O^2-), using carbon as the reducing agent. These chemical reactions are usually conducted at temperatures of several hundred degrees Celsius. Such processes are appl ...
of
sodium carbonate at 1100 °C, as the first step of the
Deville process for the production of aluminium:
:Na
2CO
3 + 2 C → 2 Na + 3 CO
The high demand for aluminium created the need for the production of sodium. The introduction of the
Hall–Héroult process
The Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) (obtained most often from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite, and el ...
for the production of aluminium by
electrolysing a molten salt bath ended the need for large quantities of sodium. A related process based on the reduction of sodium hydroxide was developed in 1886.
Sodium is now produced commercially through the
electrolysis of molten
sodium chloride, based on a process patented in 1924.
[Pauling, Linus, ''General Chemistry'', 1970 ed., Dover Publications] This is done in a
Downs cell in which the NaCl is mixed with
calcium chloride
Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide.
Ca ...
to lower the
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
below 700 °C. As
calcium is less
electropositive
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
than sodium, no calcium will be deposited at the cathode. This method is less expensive than the previous
Castner process (the electrolysis of
sodium hydroxide).
If sodium of high purity is required, it can be
distilled once or several times.
The market for sodium is volatile due to the difficulty in its storage and shipping; it must be stored under a dry
inert gas atmosphere or
anhydrous mineral oil to prevent the formation of a surface layer of
sodium oxide or
sodium superoxide.
Uses
Though metallic sodium has some important uses, the major applications for sodium use compounds; millions of tons of
sodium chloride,
hydroxide, and
carbonate are produced annually. Sodium chloride is extensively used for
anti-icing and
de-icing
Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prev ...
and as a preservative; examples of the uses of
sodium bicarbonate include baking, as a raising agent, and
sodablasting
Soda blasting is a mild form of abrasive blasting in which sodium bicarbonate particles are blasted against a surface using compressed air. It has a much milder abrasive effect than sandblasting. An early use was in the conservation-restoration of ...
. Along with potassium, many important medicines have sodium added to improve their
bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
; though potassium is the better ion in most cases, sodium is chosen for its lower price and atomic weight.
Sodium hydride is used as a base for various reactions (such as the
aldol reaction) in organic chemistry, and as a reducing agent in inorganic chemistry.
Metallic sodium is used mainly for the production of
sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applica ...
,
sodium azide,
indigo, and
triphenylphosphine. A once-common use was the making of
tetraethyllead and titanium metal; because of the move away from TEL and new titanium production methods, the production of sodium declined after 1970.
[Alfred Klemm, Gabriele Hartmann, Ludwig Lange, "Sodium and Sodium Alloys" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. ] Sodium is also used as an alloying metal, an
anti-scaling agent, and as a reducing agent for metals when other materials are ineffective.
Note the free element is not used as a scaling agent, ions in the water are exchanged for sodium ions.
Sodium plasma ("vapor") lamps are often used for street lighting in cities, shedding light that ranges from yellow-orange to peach as the pressure increases. By itself or
with potassium, sodium is a
desiccant; it gives an intense blue coloration with
benzophenone
Benzophenone is the organic compound with the formula (C6H5)2CO, generally abbreviated Ph2CO. It is a white solid that is soluble in organic solvents. Benzophenone is a widely used building block in organic chemistry, being the parent diarylket ...
when the desiccate is dry.
In
organic synthesis, sodium is used in various reactions such as the
Birch reduction, and the
sodium fusion test is conducted to qualitatively analyse compounds. Sodium reacts with alcohol and gives alkoxides, and when sodium is dissolved in ammonia solution, it can be used to reduce alkynes to trans-alkenes. Lasers emitting light at the sodium D line are used to create artificial
laser guide star
A laser guide star is an artificial star image created for use in astronomical adaptive optics systems, which are employed in large telescopes in order to correct atmospheric distortion of light (called '' astronomical seeing''). Adaptive op ...
s that
assist
Assist or ASSIST may refer to:
Sports
Several sports have a statistic known as an "assist", generally relating to action by a player leading to a score by another player on their team:
*Assist (basketball), a pass by a player that facilitates a ba ...
in the
adaptive optics
Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...
for land-based visible-light telescopes.
Heat transfer
Liquid sodium is used as a
heat transfer fluid in
sodium-cooled fast reactors
[Sodium as a Fast Reactor Coolant](_blank)
presented by Thomas H. Fanning. Nuclear Engineering Division. U.S. Department of Energy. U.S. Nuclear Regulatory Commission. Topical Seminar Series on Sodium Fast Reactors. 3 May 2007 because it has the high thermal conductivity and low neutron absorption
cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
required to achieve a high neutron flux in the reactor.
The high boiling point of sodium allows the reactor to operate at ambient (normal) pressure,
but drawbacks include its opacity, which hinders visual maintenance, and its strongly reducing properties. Sodium will explode in contact with water, although it will only burn gently in air.
Radioactive
sodium-24 may be produced by
neutron bombardment during operation, posing a slight radiation hazard; the radioactivity stops within a few days after removal from the reactor. If a reactor needs to be shut down frequently,
NaK is used. Because NaK is a liquid at room temperature, the coolant does not solidify in the pipes.
In this case, the
pyrophoricity
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
of potassium requires extra precautions to prevent and detect leaks. Another heat transfer application is
poppet valve
A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine.
It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usua ...
s in high-performance internal combustion engines; the valve stems are partially filled with sodium and work as a
heat pipe
A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.
At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor b ...
to cool the valves.
Biological role
Biological role in humans
In humans, sodium is an essential mineral that regulates
blood volume, blood pressure,
osmotic equilibrium and
pH. The minimum physiological requirement for sodium is estimated to range from about 120 milligrams per day in newborns to 500 milligrams per day over the age of 10.
Diet
Sodium chloride (
salt) is the principal source of sodium in the diet, and is used as seasoning and preservative in such commodities as
pickled preserves and
jerky
Jerky is lean trimmed meat cut into strips and dried (dehydrated) to prevent spoilage. Normally, this drying includes the addition of salt to prevent bacteria growth before the meat has finished the dehydrating process. The word "jerky" derive ...
; for Americans, most sodium chloride comes from
processed foods
Convenience food, also called tertiary processed food, is food that is commercially prepared (often through processing) to optimise ease of consumption. Such food is usually ready to eat without further preparation. It may also be easily por ...
. Other sources of sodium are its natural occurrence in food and such food additives as
monosodium glutamate (MSG),
sodium nitrite, sodium saccharin,
baking soda
Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3� ...
(sodium bicarbonate), and
sodium benzoate
Sodium benzoate is the sodium salt of benzoic acid, widely used as a food preservative (with an E number of E211) and a pickling agent. It appears as a white crystalline chemical with the formula C6H5COONa.
Production
Sodium benzoate is commo ...
.
The
U.S. Institute of Medicine set its
tolerable upper intake level
The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Re ...
for sodium at 2.3 grams per day, but the average person in the United States consumes 3.4 grams per day. The
American Heart Association recommends no more than 1.5 g of sodium per day.
High sodium consumption
High sodium consumption is unhealthy, and can lead to alteration in the mechanical performance of the heart.
High sodium consumption is also associated with
chronic kidney disease,
high blood pressure,
cardiovascular diseases, and
stroke.
= High blood pressure
=
There is a strong correlation between higher sodium intake and higher blood pressure. Studies have found that lowering sodium intake by 2 g per day tends to lower
systolic blood pressure
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
by about two to four mm Hg.
It has been estimated that such a decrease in sodium intake would lead to between 9 and 17% fewer cases of
hypertension.
Hypertension causes 7.6 million premature deaths worldwide each year. (Note that salt contains about 39.3% sodiumthe rest being chlorine and trace chemicals; thus, 2.3 g sodium is about 5.9 g, or 5.3 ml, of saltabout one
US teaspoon
A teaspoon (tsp.) is an item of cutlery. It is a small spoon that can be used to stir a cup of tea or coffee, or as a tool for measuring volume. The size of teaspoons ranges from about . For cooking purposes and dosing of medicine, a teaspoonf ...
.
)
One study found that people with or without hypertension who excreted less than 3 grams of sodium per day in their urine (and therefore were taking in less than 3 g/d) had a ''higher'' risk of death, stroke, or heart attack than those excreting 4 to 5 grams per day.
Levels of 7 g per day or more in people with hypertension were associated with higher mortality and cardiovascular events, but this was not found to be true for people without
hypertension.
The
US FDA
The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...
states that adults with hypertension and prehypertension should reduce daily sodium intake to 1.5 g.
Physiology
The
renin–angiotensin system regulates the amount of fluid and sodium concentration in the body. Reduction of blood pressure and sodium concentration in the kidney result in the production of
renin
Renin (etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the r ...
, which in turn produces
aldosterone and
angiotensin
Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adren ...
, which stimulates the reabsorption of sodium back into the bloodstream. When the concentration of sodium increases, the production of renin decreases, and the sodium concentration returns to normal. The sodium ion (Na
+) is an important electrolyte in
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
function, and in osmoregulation between cells and the
extracellular fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a low ...
. This is accomplished in all animals by
Na+/K+-ATPase, an active transporter pumping ions against the gradient, and sodium/potassium channels. Sodium is the most prevalent metallic ion in extracellular fluid.
In humans, unusually low or high sodium levels in the blood is recognized in medicine as
hyponatremia
Hyponatremia or hyponatraemia is a low concentration of sodium in the blood. It is generally defined as a sodium concentration of less than 135 mmol/L (135 mEq/L), with severe hyponatremia being below 120 mEq/L. Symptoms can be a ...
and
hypernatremia
Hypernatremia, also spelled hypernatraemia, is a high concentration of sodium in the blood. Early symptoms may include a strong feeling of thirst, weakness, nausea, and loss of appetite. Severe symptoms include confusion, muscle twitching, and b ...
. These conditions may be caused by genetic factors, ageing, or prolonged vomiting or diarrhea.
Biological role in plants
In
C4 plants, sodium is a
micronutrient that aids metabolism, specifically in regeneration of
phosphoenolpyruvate
Phosphoenolpyruvate (2-phosphoenolpyruvate, PEP) is the ester derived from the enol of pyruvate and phosphate. It exists as an anion. PEP is an important intermediate in biochemistry. It has the highest-energy phosphate bond found (−61.9 kJ/m ...
and synthesis of
chlorophyll. In others, it substitutes for
potassium in several roles, such as maintaining
turgor pressure and aiding in the opening and closing of
stomata. Excess sodium in the soil can limit the uptake of water by decreasing the
water potential, which may result in plant wilting; excess concentrations in the
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
can lead to enzyme inhibition, which in turn causes necrosis and chlorosis.
In response, some plants have developed mechanisms to limit sodium uptake in the roots, to store it in cell
vacuoles, and restrict salt transport from roots to leaves.
Excess sodium may also be stored in old plant tissue, limiting the damage to new growth.
Halophytes
A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores. T ...
have adapted to be able to flourish in sodium rich environments.
Safety and precautions
Sodium forms flammable hydrogen and caustic
sodium hydroxide on contact with water; ingestion and contact with moisture on skin, eyes or
mucous membrane
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
s can cause severe burns.
Sodium spontaneously explodes in the presence of water due to the formation of hydrogen (highly explosive) and sodium hydroxide (which dissolves in the water, liberating more surface). However, sodium exposed to air and ignited or reaching autoignition (reported to occur when a molten pool of sodium reaches about ) displays a relatively mild fire.
In the case of massive (non-molten) pieces of sodium, the reaction with oxygen eventually becomes slow due to formation of a protective layer.
Fire extinguisher
A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which ha ...
s based on water accelerate sodium fires. Those based on carbon dioxide and
bromochlorodifluoromethane should not be used on sodium fire.
Metal fires are
Class D, but not all Class D extinguishers are effective when used to extinguish sodium fires. An effective extinguishing agent for sodium fires is Met-L-X.
Other effective agents include Lith-X, which has
graphite powder and an
organophosphate flame retardant
The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...
, and dry sand.
Sodium fires are prevented in nuclear reactors by isolating sodium from oxygen with surrounding pipes containing inert gas.
Pool-type sodium fires are prevented using diverse design measures called catch pan systems. They collect leaking sodium into a leak-recovery tank where it is isolated from oxygen.
Liquid sodium fires are more dangerous to handle than solid sodium fires, particularly if there is insufficient experience with the safe handling of molten sodium. In a technical report for the
United States Fire Administration,
R. J. Gordon writes (emphasis in original)
See also
References
Bibliography
*
External links
Sodiumat ''
The Periodic Table of Videos
''Periodic Videos'' (also known as ''The Periodic Table of Videos'') is a video project and YouTube channel on chemistry. It consists of a series of videos about chemical elements and the periodic table, with additional videos on other topics i ...
'' (University of Nottingham)
Etymology of "natrium" – source of symbol Na
{{Authority control
Chemical elements
Alkali metals
Sodium minerals
Desiccants
Dietary minerals
Reducing agents
Nuclear reactor coolants
Chemical elements with body-centered cubic structure