SODIUM: HISTORY, STRUCTURE, PROPERTIES, RISKS AND USES - CHEMISTRY - 2025

The sodium is an alkali metal of Group 1 of the periodic table. Its atomic number is 11 and it is represented by the chemical symbol Na. It is a light metal, less dense than water, silver-white in color that turns gray when exposed to air; that is why it is stored in paraffins or noble gases.

In addition, it is a soft metal that can be cut with a knife and becomes brittle at low temperatures. Reacts explosively with water to form sodium hydroxide and hydrogen gas; It also reacts with humid air and with the humidity of bare hands.

Metallic sodium stored in a bottle and immersed in oil so that it does not react with air. Source: Hi-Res Images of Chemical Elements

This metal is found in rock salt minerals such as halite (sodium chloride), in brines, and in the sea. Sodium chloride represents 80% of all materials dissolved in the sea, sodium having an abundance of 1.05%. It is the sixth element in abundance in the earth's crust.

The analysis of the spectra of the light coming from the stars has made it possible to detect their presence in them, including the Sun. Likewise, their presence in meteorites has been determined.

Sodium is a good thermal and electrical conductor, as well as having a great heat absorption capacity. It experiences the photoelectric phenomenon, that is, it is capable of emitting electrons when it is illuminated. When burned, its flame emits an intense yellow light.

Molten sodium acts as a heat transfer agent, which is why it is used as a coolant in certain nuclear reactors. It is also used as a metal deoxidizer and reducer, which is why it has been used in the purification of transition metals, such as titanium and zirconium.

Sodium is the main contributor to the osmolarity of the extracellular compartment and its volume. Likewise, it is responsible for the generation of action potentials in excitable cells and the initiation of muscle contraction.

Excessive sodium intake can cause: cardiovascular diseases, increased risk of strokes, osteoporosis due to the mobilization of bone calcium and kidney damage.

History

Man has used sodium compounds since ancient times, especially sodium chloride (common salt) and sodium carbonate. The importance of salt is evidenced by the use of the Latin word "salarium" to indicate a portion of salt that the soldiers received as part of the payment.

In the Middle Ages a sodium compound was used with the Latin name "sodanum", which meant headache.

In 1807, Sir Humprey Davy isolated sodium by electrolysis of sodium hydroxide. Davy also isolated potassium, at a time when sodium hydroxide and potassium hydroxide were regarded as elemental substances and called fixed alkalis.

Davy in a letter to a friend, wrote: “I decomposed and recomposed the fixed alkalis and discovered that their bases were two new very flammable substances similar to metals; but one of them is more flammable than the other and very reactive ”.

In 1814, Jöns Jakob in his System of Chemical Symbols used the abbreviation Na for the Latin word 'natrium', in order to name sodium. This word comes from the Egyptian 'natron' name used to refer to sodium carbonate.

Structure and electron configuration of sodium

Metallic sodium crystallizes into a body-centered cubic (bcc) structure. Therefore, its Na atoms are positioned to form cubes, with one located in the center and each with eight neighbors.

This structure is characterized by being the least dense of all, which agrees with the low density for this metal; so low, that it is together with lithium and potassium, the only metals that can float in liquid water (before exploding, of course). Its low atomic mass, relative to its voluminous atomic radius, also contributes to this property.

The resulting metallic bond, however, is quite weak, and can be explained from the electronic configuration:

3s ¹

The electrons in the closed shell do not participate (at least under normal conditions) in the metallic bond; but the electron in the 3s orbital. Na atoms overlap their 3s orbitals to create a valence band; and the 3p, empty, a conduction band.

This 3s band, being half full, as well as due to the low density of the crystal, makes the force, governed by the "sea of ​​electrons", weak. Consequently, metallic sodium can be cut with a metal and melts only at 98ºC.

Phase transitions

The sodium crystal can undergo changes in its structure when experiencing increases in pressure; while when heated, it is unlikely to undergo phase transitions due to its low melting point.

Once phase transitions start, the properties of the metal change. For example, the first transition generates a face-centered cubic (fcc) structure. Thus, the sparse structure bcc is compacted to fcc by pressing the metallic sodium.

This may not produce an appreciable change in the properties of sodium other than in its density. However, when the pressures are very high, the allotropes (not polymorphic since they are a pure metal) surprisingly become insulators and electrides; that is, even the electrons are fixed in the crystal as anions and do not circulate freely.

In addition to the above said, their colors also change; sodium stops being greyish to become dark, reddish or even transparent, as operating pressures rise.

Oxidation numbers

Given the 3s valence orbital, when sodium loses its only electron, it rapidly transforms into the Na ⁺ cation, which is isoelectronic to neon. That is, both Na ⁺ and Ne have the same number of electrons. If the presence of Na ⁺ in the compound is assumed, then its oxidation number is said to be +1.

Whereas if the opposite happens, that is, sodium gaining an electron, its resulting electron configuration is 3s ²; now it is isoelectronic with magnesium, being the Na anion ^- called sodium. If the presence of Na ^- in the compound is assumed, then sodium will have an oxidation number of -1.

Properties

An ethyl sodium chloride solution burning to manifest the characteristic yellow color of the flame for this metal. Source: Der Messer

Physical description

Soft, ductile, malleable light metal.

Atomic weight

22.989 g / mol.

Color

Sodium is a light silvery metal. Shiny when freshly cut, but loses its luster when it is put in contact with air, becoming opaque. Soft at temperature, but quite hard at -20 ºC.

Boiling point

880 ° C.

Melting point

97.82 ºC (almost 98 ºC).

Density

At room temperature: 0.968 g / cm ³.

In liquid state (melting point): 0.927 g / cm ³.

Solubility

Insoluble in benzene, kerosene and naphtha. It dissolves in liquid ammonia, giving a blue colored solution. It dissolves in mercury forming an amalgam.

Vapor pressure

Temperature 802 K: 1 kPa; that is, its vapor pressure is considerably low even at high temperatures.

Decomposition

It decomposes violently in water, forming sodium hydroxide and hydrogen.

Auto ignition temperature

120-125 ° C.

Viscosity

0.680 cP at 100 ° C

Surface tension

192 dynes / cm at melting point.

Refractive index

4.22.

Electronegativity

0.93 on the Pauling scale.

Ionization energy

First ionization: 495.8 kJ / mol.

Second ionization: 4,562 kJ / mol.

Third ionization: 6,910.3 kJ / mol.

Atomic radio

186 pm.

Covalent radius

166 ± 9 pm.

Thermal expansion

71 µm (m · K) at 26 ° C.

Thermal conductivity

132.3 W / m K at 293.15 K.

Electrical resistivity

4.77 × 10 ^-8 Ωm at 293 K.

Nomenclature

Because sodium has a unique oxidation number of +1, the names of its compounds, governed by the stock nomenclature, are simplified as this number is not specified in parentheses and with Roman numerals.

In the same way, their names according to traditional nomenclature all end with the suffix -ico.

For example, NaCl is sodium chloride according to the stock nomenclature, being sodium chloride (I) erroneous. It is also called sodium monochloride, according to the systematic nomenclature; and sodium chloride, according to traditional nomenclature. However, its most common name is table salt.

Biological role

Osmotic component

Sodium has an extracellular concentration of 140 mmol / L, being in ionic form (Na ⁺). To maintain the electroneutrality of the extracellular compartment, Na ⁺ is accompanied by chloride (Cl ^-) and bicarbonate (HCO ₃ ^-) anions, with concentrations of 105 mmol / L and 25 mmol / L respectively.

The Na ⁺ cation is the main osmotic component and has the greatest contribution to the osmolarity of the extracellular compartment, such that there is an equality of osmolarity between the extracellular and intracellular compartments that guarantees the integrity of the intracellular compartment.

On the other hand, the intracellular concentration of Na ⁺ is 15 mmol / L. So: Why are the extra and intracellular Na ⁺ concentrations not equalized ?

There are two reasons why this does not occur: a) the plasma membrane is poorly permeable to Na ⁺. b) the existence of the Na ⁺ -K ⁺ pump.

The pump is an enzymatic system in the plasma membrane that uses the energy contained in ATP to remove three Na ⁺ atoms and introduce two K ⁺ atoms.

In addition, there is a set of hormones, including aldosterone, which, by promoting renal sodium reabsorption, guarantees the maintenance of the extracellular sodium concentration at its proper value. Antidiuretic hormone helps maintain extracellular volume.

Production of action potentials

Excitable cells (neurons and muscle cells) are those that respond to an appropriate stimulus with the formation of an action potential or nerve impulse. These cells maintain a voltage difference across the plasma membrane.

The cell interior is negatively charged relative to the cell exterior under resting conditions. Given a certain stimulus, there is an increase in the permeability of the membrane to Na ⁺ and a small amount of Na ⁺ ions enters the cell, causing the cell interior to become positively charged.

The above is what is known as an action potential, which can propagate throughout a neuron and is the way information travels through it.

When the action potential reaches muscle cells, it stimulates them to contract through more or less complex mechanisms.

In summary, sodium is responsible for the production of action potentials in excitable cells and for the initiation of muscle cell contraction.

Where is it located

Earth crust

Sodium is the seventh most abundant element in the earth's crust, representing 2.8% of it. Sodium chloride is part of the mineral halite, which represents 80% of the dissolved materials in the sea. The sodium content of the sea is 1.05%.

Sodium is a very reactive element, which is why it is not found in its native or elemental form. It is found in soluble minerals like halite or insoluble minerals like cryolite (a sodium aluminum fluoride).

Sea and the mineral halite

Besides the sea in general, the Dead Sea is characterized by having a very high concentration of different salts and minerals, especially sodium chloride. The Great Salt Lake in the United States also has a high concentration of sodium.

Sodium chloride is found almost pure in the mineral halite, present in the sea and in rock structures. Rock or mineral salt is less pure than halite, found in mineral deposits in Great Britain, France, Germany, China, and Russia.

Saline deposits

Salt is extracted from its rocky deposits by fragmentation of the rocks, followed by a process of purification of the salt. At other times, water is introduced into the salt tanks to dissolve it and form a brine, which is then pumped to the surface.

Salt is obtained from the sea in shallow basins known as salinas, through solar evaporation. The salt obtained in this way is called bay salt or sea salt.

Downs cell

Sodium was produced by the carbothermic reduction of sodium carbonate carried out at 1,100ºC. Currently, it is produced by the electrolysis of molten sodium chloride, using the Downs cell.

However, since molten sodium chloride has a melting point of ~ 800 ° C, calcium chloride or sodium carbonate is added to lower the melting point to 600 ° C.

In the Downs chamber, the cathode is made of iron in a circular shape, around a carbon anode. The electrolysis products are separated by a steel mesh to prevent the electrolysis products from coming into contact: elemental sodium and chlorine.

At the anode (+) the following oxidation reaction occurs:

2 Cl ^- (l) → Cl ₂ (g) + 2 e ^-

Meanwhile, at the cathode (-) the following reduction reaction occurs:

2 Na ⁺ (l) + 2 e ^- → 2 Na (l)

Reactions

Formation of oxides and hydroxide

It is very reactive in air depending on its humidity. It reacts to form a film of sodium hydroxide, which can absorb carbon dioxide and eventually form sodium bicarbonate.

It oxidizes in air to form sodium monoxide (Na ₂ O). While sodium superoxide (NaO ₂) is prepared by heating metallic sodium to 300 ºC with oxygen at high pressure.

In liquid state it ignites at 125ºC, producing an irritating white smoke, capable of producing coughing. It also reacts vigorously with water to produce sodium hydroxide and hydrogen gas, causing the reaction to explode. This reaction is strongly exothermic.

Na + H ₂ O → NaOH + 1/2 H ₂ (3,367 kilocalories / mol)

With halogenated acids

Halogenated acids, such as hydrochloric acid, react with sodium to form the corresponding halides. Meanwhile, its reaction with nitric acid generates sodium nitrate; and with sulfuric acid, it generates sodium sulfate.

Reductions

Na reduces the oxides of the transition metals, producing the corresponding metals by freeing them from oxygen. Also, sodium reacts with the halides of the transition metals, causing the displacement of the metals to form sodium chloride and releasing the metals.

This reaction has served to obtain transition metals, including titanium and tantalum.

With ammonia

Sodium reacts with liquid ammonia at low temperature and slowly to form sodamide (NaNH ₂) and hydrogen.

Na + NH ₃ → NaNH ₂ + 1/2 H ₂

Liquid ammonia serves as a solvent for the reaction of sodium with various metals, including arsenic, tellurium, antimony, and bismuth.

Organic

Reacts with alcohols to produce alcoholates or alkoxides:

Na + ROH → RONa + 1/2 H ₂

It produces the dehalogenation of organic compounds, causing a doubling in the number of carbons of the compound:

2 Na + 2 RCl → RR + 2 NaCl

Octane can be produced by the dehalogenation of butane bromide with sodium.

With metals

Sodium can react with other alkali metals to form a eutectic: an alloy that forms at lower temperatures than its components; for example, NaK which has a K percentage of 78%. Also sodium forms alloys with beryllium with a small percentage of the former.

Precious metals like gold, silver, platinum, palladium, and iridium, as well as white metals like lead, tin, and antimony, form alloys with liquid sodium.

Risks

It is a metal that reacts strongly with water. Therefore, in contact with human tissues coated with water can cause severe damage. Produces severe burns on contact with skin and eyes.

Likewise, by ingestion it can cause perforation of the esophagus and stomach. However, although these injuries are serious, only a small proportion of the population is exposed to them.

The greatest damage that sodium can cause is due to its excessive intake in foods or drinks made by people.

The human body requires a sodium intake of 500 mg / day, to fulfill its function in nerve conduction, as well as in muscle contraction.

But usually a much higher amount of sodium is ingested in the diet, which produces an increase in plasma and blood concentration of it.

This can cause high blood pressure, cardiovascular disease, and strokes.

Hypernatremia is also associated with the generation of osteoporosis by inducing an outflow of calcium from bone tissue. The kidneys have trouble maintaining a normal plasma sodium concentration despite excessive intake, which can lead to kidney damage.

Applications

Metallic sodium

It is used in metallurgy as a deoxidizing and reducing agent in the preparation of calcium, zirconium, titanium and other metals. For example, it reduces titanium tetrachloride (TiCl ₄) to produce metallic titanium.

Molten sodium is used as a heat transfer agent, which is why it is used as a coolant in some nuclear reactors.

It is used as a raw material in the manufacture of sodium lauryl sulfate, the main ingredient in synthetic detergent. It is also involved in the manufacture of polymers such as nylon and compounds such as cyanide and sodium peroxide. Also in the production of dyes and perfume synthesis.

Sodium is used in the purification of hydrocarbons and in the polymerization of insoluble hydrocarbons. It is also used in many organic reductions. Dissolved in liquid ammonia it is used to reduce alkynes to transalkene.

Sodium vapor lamps are built for public lighting in cities. These provide a yellow color, similar to that observed when sodium is burned in lighters.

Sodium acts as a desiccant that provides a blue coloration in the presence of benzophenone, indicating that the product in the drying process has reached the desired drying.

Compounds

Chloride

It is used to season and preserve food. The electrolysis of sodium chloride produces sodium hypochlorite (NaOCl), used in household cleaning as chlorine. In addition, it is used as an industrial bleach for paper and textile pulp or in water disinfection.

Sodium hypochlorite is used in certain medicinal preparations as an antiseptic and fungicide.

Carbonate and bicarbonate

Sodium carbonate is used in the manufacture of glasses, detergents, and cleaners. Sodium carbonate monohydrate is used in photography as a developer component.

Baking soda is a source of carbon dioxide. For this reason it is used in baking powders, in salts and effervescent drinks and also in dry chemical fire extinguishers. It is also used in the process of tanning and preparing wool.

Sodium bicarbonate is an alkaline compound, used in the medicinal treatment of gastric and urinary hyperacidity.

Sulfate

It is used in the manufacture of kraft paper, cardboard, glass and detergents. Sodium thiosulfate is used in photography in order to correct negatives and developed prints.

Hydroxide

Commonly called caustic soda or lye, it is used in the neutralization of acids in petroleum refining. Reacts with fatty acids in making soap. In addition, it is used in the treatment of cellulose.

Nitrate

It is used as a fertilizer that provides nitrogen, being a component of dynamite.

References

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