Sodium is a
chemical element with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
Na (from Latin ''natrium'') and
atomic number 11. It is a soft, silvery-white, highly reactive
metal. Sodium is an
alkali metal
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
, being in
group 1 of the periodic table. Its only stable
isotope 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 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 minerals over eons, and thus sodium and
chlorine are the most common dissolved elements by weight in the oceans.
Sodium was first isolated by
Humphry Davy in 1807 by the
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of
sodium hydroxide
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 ...
. Among many other useful sodium compounds,
sodium hydroxide
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 ...
(
lye) is used in
soap manufacture, and
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
(
edible salt) is a
de-icing 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 (ECF) and as such are the major contributor to the ECF
osmotic pressure
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a solution to take in a pure ...
and ECF compartment volume. Loss of water from the ECF compartment increases the sodium concentration, a condition called
hypernatremia.
Isotonic loss of water and sodium from the ECF compartment decreases the size of that compartment in a condition called ECF
hypovolemia
Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the los ...
.
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
Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union o ...
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 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 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
allotrope
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: the ...
s are insulators and
electrides.
In a
flame test, sodium and its compounds glow yellow because the excited
3s electrons of sodium emit a
photon 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 structure
In atomic physics, hyperfine structure is defined by small shifts in otherwise degenerate energy levels and the resulting splittings in those energy levels of atoms, molecules, and ions, due to electromagnetic multipole interaction between the nucl ...
s 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 atoms together; this requires temperatures above 600 megakelvins and a star of at least three solar masses. Two
radioactive,
cosmogenic isotopes are the byproduct of
cosmic ray spallation:
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 isomers 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, 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 neon
Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypton ...
. The first and second
ionization energies are 495.8 kJ/mol and 4562 kJ/mol, respectively. As a result, sodium usually forms
ionic compound
In chemistry, an ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding. The compound is neutral overall, but consists of positively charged ions called cations and negatively charged i ...
s 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
Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
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. 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,
paper,
soap, and
textiles.
The most important sodium compounds are
table salt (Na
Cl),
soda ash (Na
2 CO3),
baking soda (Na
HCO3),
caustic soda (NaOH),
sodium nitrate
Sodium nitrate is the chemical compound with the formula . This alkali metal nitrate salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordinary saltpeter, potassium nitrate. T ...
(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
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
.
Most
soaps 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 metal
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
s, sodium reacts
exothermically with water. The reaction produces caustic soda (
sodium hydroxide
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 ...
) and flammable
hydrogen 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,
sulfates,
nitrates
Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble ...
,
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; for example, only 0.35 g/L of sodium chloride will dissolve in ethanol.
Crown ethers, 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 (Na(NH
3)
6)
+, with the positive charge counterbalanced by
electrons as anions;
cryptands 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
ionophores, also have a high affinity for the sodium ion; derivatives of the
alkalide 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
carbanion
In organic chemistry, a carbanion is an anion in which carbon is trivalent (forms three bonds) and bears a formal negative charge (in at least one significant resonance form).
Formally, a carbanion is the conjugate base of a carbon acid:
:R3C ...
s (salts with organic
anions). Some well-known derivatives include
sodium cyclopentadienide (NaC
5H
5) and trityl sodium ((C
6H
5)
3CNa).
Sodium naphthalene, 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, and the
group 11
Group 11, by modern IUPAC numbering, is a group of chemical elements in the periodic table, consisting of copper (Cu), silver (Ag), and gold (Au), and roentgenium (Rg), although no chemical experiments have yet been carried out to confirm that ...
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
Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies ...
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 (NaAg
2). Group 12 metals (
zinc,
cadmium and
mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
) 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
Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches.
Headaches can occur as a result ...
remedy. The name sodium is thought to originate from the Arabic ''suda'', meaning headache, as the headache-alleviating properties of
sodium carbonate
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 ...
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 through the
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of
sodium hydroxide
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 ...
.
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 name ''natrium'', which refers to the Egyptian ''
natron'',
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 Kirchhoff, Kirchoff or Kirchhoffer is a German surname. Notable people with the surname include:
* Adolf Kirchhoff (1826–1908), German classical scholar and epigrapher
* Alfred Kirchhoff (1838–1907), German geographer and naturalist
* Alphonse ...
and
Bunsen Bunsen may refer to:
* Christian Charles Josias Bunsen (1791–1860), Prussian diplomat and scholar
* Frances Bunsen (1791–1876), or Baroness Bunsen, Welsh painter and author, wife of Christian Charles Josias Bunsen
* Robert Bunsen (1811–1899), ...
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,
iron,
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, others much less soluble, such as
amphibole
Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...
and
zeolite. The insolubility of certain sodium minerals such as
cryolite 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
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
in many types of stars, including the
Sun. The line was first studied in 1814 by
Joseph von Fraunhofer
Joseph Ritter von Fraunhofer (; ; 6 March 1787 – 7 June 1826) was a German physicist and optical lens manufacturer. He made optical glass, an achromatic telescope, and objective lenses. He also invented the spectroscope and developed diffract ...
during his investigation of the lines in the solar spectrum, now known as the
Fraunhofer lines. 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
In atomic physics, hyperfine structure is defined by small shifts in otherwise degenerate energy levels and the resulting splittings in those energy levels of atoms, molecules, and ions, due to electromagnetic multipole interaction between the nucl ...
.
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
In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
. The two can be distinguished via high-resolution spectroscopy, because interstellar lines are much narrower than those broadened by
stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
The rotation of a star produces an equatorial bulge ...
.
Sodium has also been detected in numerous
Solar System environments, including
Mercury's atmosphere, the
exosphere
The exosphere ( grc, ἔξω "outside, external, beyond", grc, σφαῖρα "sphere") is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the densit ...
of the
Moon, and numerous other bodies. Some
comets have a
sodium tail, which was first detected in observations of
Comet Hale–Bopp in 1997.
Sodium has even been detected in the atmospheres of some
extrasolar planets via
transit spectroscopy
Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty ...
.
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 of
sodium carbonate
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 ...
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 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
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of molten
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
, 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 to lower the
melting point below 700 °C. As
calcium is less
electropositive 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
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 ...
).
If sodium of high purity is required, it can be
distilled
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating ...
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
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
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
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
,
hydroxide, and
carbonate are produced annually. Sodium chloride is extensively used for
anti-icing and
de-icing and as a preservative; examples of the uses of
sodium bicarbonate
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−) ...
include baking, as a raising agent, and
sodablasting. Along with potassium, many important medicines have sodium added to improve their
bioavailability; 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 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
A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...
; it gives an intense blue coloration with
benzophenone when the desiccate is dry.
In
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
, 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 stars that
assist in the
adaptive optics for land-based visible-light telescopes.
Heat transfer
Liquid sodium is used as a
heat transfer fluid in
sodium-cooled fast reactor
A sodium-cooled fast reactor is a fast neutron reactor cooled by liquid sodium.
The initials SFR in particular refer to two Generation IV reactor proposals, one based on existing liquid metal cooled reactor (LMFR) technology using mixed oxide fue ...
s
[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 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
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beha ...
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 of potassium requires extra precautions to prevent and detect leaks. Another heat transfer application is
poppet valves in high-performance internal combustion engines; the valve stems are partially filled with sodium and work as a
heat pipe 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
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
(
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; for Americans, most sodium chloride comes from
processed foods. 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), and
sodium benzoate.
The
U.S. Institute of Medicine
The National Academy of Medicine (NAM), formerly called the Institute of Medicine (IoM) until 2015, is an American nonprofit, non-governmental organization. The National Academy of Medicine is a part of the National Academies of Sciences, Eng ...
set its
tolerable upper intake level 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
The American Heart Association (AHA) is a nonprofit organization in the United States that funds cardiovascular medical research, educates consumers on healthy living and fosters appropriate cardiac care in an effort to reduce disability and death ...
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
Chronic kidney disease (CKD) is a type of kidney disease in which a gradual loss of kidney function occurs over a period of months to years. Initially generally no symptoms are seen, but later symptoms may include leg swelling, feeling tired, vo ...
,
high blood pressure
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
,
cardiovascular disease
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...
s, and
stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
.
= 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 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 (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
.
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.
)
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
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...
.
The
US FDA 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, which in turn produces
aldosterone
Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
and
angiotensin, 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 function, and in osmoregulation between cells and the
extracellular fluid. 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 and
hypernatremia. These conditions may be caused by genetic factors, ageing, or prolonged vomiting or diarrhea.
Biological role in plants
In
C4 plants
carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960's discovery by Marshall Davidson Hatch and Charles Roger Slack that some plants, when suppl ...
, sodium is a
micronutrient
Micronutrients are nutrient, essential dietary elements required by organisms in varying quantities throughout life to orchestrate a range of physiological functions to maintain health. Micronutrient requirements differ between organisms; for exam ...
that aids metabolism, specifically in regeneration of
phosphoenolpyruvate and synthesis of
chlorophyll
Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...
. In others, it substitutes for
potassium in several roles, such as maintaining
turgor pressure and aiding in the opening and closing of
stoma
In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
ta. Excess sodium in the soil can limit the uptake of water by decreasing the
water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and ...
, which may result in plant wilting; excess concentrations in the
cytoplasm 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 have adapted to be able to flourish in sodium rich environments.
Safety and precautions
Sodium forms flammable hydrogen and caustic
sodium hydroxide
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 ...
on contact with water; ingestion and contact with moisture on skin, eyes or
mucous membranes 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 extinguishers based on water accelerate sodium fires. Those based on carbon dioxide and
bromochlorodifluoromethane
Bromochlorodifluoromethane (BCF), also referred to by the code numbers Halon 1211 and Freon 12B1, is a haloalkane with the chemical formula C F2 Cl Br. It is used for fire suppression, especially for expensive equipment or items that could be d ...
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
In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered a ...
flame retardant, 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
The United States Fire Administration (USFA) is a division of the Federal Emergency Management Agency (FEMA) located in unincorporated Frederick County, Maryland, near Emmitsburg. Per the official website, "the mission of the U.S. Fire Administra ...
,
R. J. Gordon writes (emphasis in original)
See also
References
Bibliography
*
External links
Sodiumat ''
The Periodic Table of Videos'' (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