sodium

[SOD(A) + -IUM.]

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A chemical element, Na, atomic number 11, and atomic weight 22.9898. Sodium is between lithium and potassium in the periodic table. The element is a soft, reactive, low-melting metal with a specific gravity of 0.97 at 20°C (68°F). Sodium is commercially the most important alkali metal. The physical properties of metallic sodium are summarized in the table below. See also Periodic table.

Sodium ranks sixth in abundance among all the elements in the Earth's crust, which contains 2.83% sodium in combined form. Only oxygen, silicon, aluminum, iron, and calcium are more abundant. Sodium is, after chlorine, the second most abundant element in solution in seawater. The important sodium salts found in nature include sodium chloride (rock salt), sodium carbonate (soda and trona), sodium borate (borax), sodium nitrate (Chile saltpeter), and sodium sulfate. Sodium salts are found in seawater, salt lakes, alkaline lakes, and mineral springs. See also Alkali metals.

Sodium reacts rapidly with water, and even with snow and ice, to give sodium hydroxide and hydrogen. The reaction liberates sufficient heat to melt the sodium and ignite the hydrogen. When exposed to air, freshly cut sodium metal loses its silvery appearance and becomes dull gray because of the formation of a coating of sodium oxide.

Sodium does not react with nitrogen. Sodium and hydrogen react above about 200°C (390°F) to form sodium hydride. Sodium reacts with ammonia, forming sodium amide. Sodium also reacts with ammonia in the presence of coke to form sodium cyanide.

Sodium does not react with paraffin hydrocarbons but does form addition compounds with naphthalene and other polycyclic aromatic compounds and with arylated alkenes. The reaction of sodium with alcohols is similar to, but less rapid than, the reaction of sodium with water. Sodium reacts with organic halides in two general ways. One of these involves condensation of two organic, halogen-bearing compounds by removal of the halogen, allowing the two organic radicals to join directly. The second type of reaction involves replacement of the halogen by sodium, giving an organosodium compound. See also Organometallic compound.

Sodium chloride, or common salt, NaCl, is not only the form in which sodium is found in nature but (in purified form) is the most important sodium compound in commerce as well. Sodium hydroxide, NaOH, is also commonly known as caustic soda. Sodium carbonate, Na₂CO₃, is best known under the name soda ash.

The largest single use for sodium metal, accounting for about 60% of total production, is in the synthesis of tetraethyllead, an antiknock agent for automotive gasolines. A second major use is in the reduction of animal and vegetable oils to long-chain fatty alcohols; these alcohols are raw materials for detergent manufacture. Sodium is used to reduce titanium and zirconium halides to their respective metals. Sodium chloride is used in curing fish, meat packing, curing hides, making freezing mixtures, and food preparation (including canning and preserving). Sodium hydroxide is used in the manufacture of chemicals, cellulose film, rayon soap pulp, and paper. Sodium carbonate is used in the glass industry and in the manufacture of soap, detergents, various cleansers, paper and textiles, nonferrous metals, and petroleum products. Sodium sulfate (salt cake) is used in the pulp industry and in the manufacture of flat glass.

The sodium ion (Na⁺) is the main positive ion present in extracellular fluids and is essential for maintenance of the osmotic pressure and of the water and electrolyte balances of body fluids. Hydrolysis of adenosine triphosphate (ATP) is mediated by the membrane-bound enzyme Na⁺,K⁺-ATPase (this enzyme is also called sodium pump). The potential difference associated with the transmembrane sodium and potassium ion gradients is important for nerve transmission and muscle contraction. Sodium ion gradients are also responsible for various sodium ion–dependent transport processes, including sodium-proton exchange in the heart, sugar transport in the intestine, and sodium-lithium exchange and amino acid transport in red blood cells. See also Adenosine triphosphate (ATP); Potassium.

A dietary essential mineral; requirements are almost invariably satisfied by the normal diet. The body contains about 100 g of sodium and the average diet contains 3-6 g, equivalent to 7.5-15 g of sodium chloride (salt); the requirement is less than 0.5 g sodium/day. The intake varies widely between individuals and excretion varies accordingly. Excessive intake of sodium is associated with hypertension. See also salt-free diets; salt lick; sodium-potassium ratio; water balance.

A metallic element which is an important constituent of the human body. Sodium plays a major role in water balance.

Sodium is one of the major components of table salt. An investigation, called the Intersalt Study, of 10 000 people from 32 countries, found that there was a very strong correlation between a high sodium consumption and high blood pressure, especially in sodium-sensitive people. The results can be interpreted in a number of ways, but most dietitians agree that high sodium intakes can be harmful. Sodium can also increase the risk of oedema (swelling, particularly in joints, caused by an accumulation of fluids). The current average sodium intake of adults in the UK is 3.2 g per day. The government recommends that this should be decreased to 1.6 g. One simple way of reducing sodium intake is not to add table salt to food.

Sodium deficiency is rare, but it can occur if losses from heavy sweating are not replaced. A deficiency leads to nausea and muscular cramps. See also table salt.

A soft, grayish metal of the alkaline metals group. Its atomic number is 11, and its atomic weight is 22.9898. Sodium is one of the most important elements in the body. Sodium ions are involved in acid-base balance, water balance, the transmission of nerve impulses, and the contraction of muscle. The recommended daily intake of sodium is 250 to 750 mg for infants, 900 to 2,700 mg for children, and 1,100 to 3,300 mg for adults.

Description

Known to most people in the form of table salt, sodium is one of the minerals that the body needs in relatively large quantities. Humankind's taste for sodium reaches far back into the distant past. Much like today, sodium was popular in antiquity as a food preservative and an ingredient in snacks. In some ancient societies, sodium was even used as a form of currency.

In modern times, most Americans and other Westerners consume far too much of the mineral, and it is easy to see why. One obvious culprit is table salt, which has a high sodium content. The mineral is also found in many of America's favorite foods (or the chemicals used to preserve those foods). Sodium can be found in potato chips and a variety of other snacks, processed foods, meat, fish, butter and margarine, soft drinks, dairy products, canned vegetables, and bread, just to name a few sources. A single slice of pizza can supply the body with all the sodium it needs for one day (about 500 mg), while a teaspoon of table salt contains four times that amount.

A certain intake of sodium is considered essential to life. The mineral is a vital component of all bodily fluids, including blood and sweat. Often working in combination with other minerals such as potassium, sodium helps to manage the distribution and pH balance of these fluids inside the body and plays an important role in blood pressure regulation. Sodium is referred to as an electrolyte because it possesses a mild electrical charge when dissolved in bodily fluids. Due to this charge, sufficient amounts of the mineral are necessary for the normal functioning of nerve transmissions and muscle contractions. Sodium also helps the body to retain water and prevent dehydration, and may have some activity as an antibacterial.

The important benefits associated with sodium become apparent in cases of sodium deficiency, which is relatively uncommon. Sodium deficiency is most likely to occur in cases of starvation, diarrhea, intense sweating, or other conditions that cause rapid loss of water from the body. People who suffer from low sodium levels may experience a wide range of bothersome or serious health problems, including digestive disorders, muscle twitching or weakness, memory loss, fatigue, and lack of concentration or appetite. Arthritis may also develop. These problems usually occur when fluids that belong in the bloodstream take a wrong turn and enter cells.

General Use

Most Americans consume anywhere from 3,000 mg to 20,000 mg of sodium a day. These amounts are much more than the body needs to function at an optimal level. Many nutrition experts are concerned about the rise in sodium intake in the general population in the last twenty years. Much of this increase is due to the popularity of fast foods and salty snacks, including the sale of high-sodium snack foods in school cafeterias or vending machines.

While sodium deficiencies are rare, supplements may be required in people with certain medical conditions such as Addison's disease, adrenal gland tumors, kidney disease, or low blood pressure. More sodium may also be needed by those who experience severe dehydration or by people who take diuretic drugs.

Though taking extra amounts of sodium is not known to improve health or cure disease, the mineral may have some therapeutic value when used externally. A number of medical studies in people suggest that soaking in water from the Dead Sea may be beneficial in the treatment of various diseases such as rheumatoid arthritis, psoriatic arthritis, and osteoarthritis of the knees. Located in Israel, the Dead Sea is many times saltier than ocean water and rich in other minerals such as magnesium, potassium, and calcium. In one small study, published in 1995 by researchers from the Soroka Medical Center in Israel, nine people with rheumatoid arthritis showed significant improvement in their condition after bathing in the Dead Sea for 12 days. The control group in the study, whose members did not bathe in the Dead Sea, failed to improve. The beneficial effects of the Dead Sea soaks lasted for up to three months after they had stopped bathing in the famous body of water. Despite intriguing findings such as these, no one knows for certain if sodium plays a major role in the therapeutic powers associated with the Dead Sea soaks.

Sodium has a reputation as a germ killer. Some people use a sodium solution as an antibacterial mouthwash to combat microorganisms that cause sore throat or inflamed gums. Plain saltwater soaks have also been recommended as a remedy for sweaty feet. Salt is believed to have a drying effect by soaking up excess perspiration. In ages past, saltwater soaks were used to relieve sore or aching muscles.

Preparations

In the late 1990s the National Academy of Sciences established the recommended daily allowance (RDA) of sodium as between 1,100 and 3,300 milligrams.

To prepare a sodium mouthwash, mix 1 tsp of table salt with a glass of warm water. The solution should be swished around in the mouth for about a minute or so. Then spit the mixture out. Try not to swallow the solution, as it contains about 2,000 mg of sodium.

Sodium is available in tablet form, but supplements should only be taken under the supervision of a doctor. As mentioned earlier, most people already get far too much sodium in their diets.

A trip to the Dead Sea is not necessary in order to enjoy its potential benefits. Dead Sea bath salts are also available.

Precautions

People who wish to take sodium supplements or increase their sodium intake should talk to a doctor first if they have high blood pressure (or a family history of the disease), congestive heart failure (or other forms of heart or blood vessel disease), hepatic cirrhosis, edema, epilepsy, kidney disease, or bleeding problems.

Studies investigating the role of sodium in the development of high blood pressure have produced mixed results. However, sodium is widely believed to contribute to the development of the disease in susceptible people. For this reason, most doctors and major health organizations around the world recommend a diet low in sodium. Eating a low-sodium diet may actually help to lower blood pressure, especially when that diet includes sufficient amounts of potassium.

A 20-year-long follow-up study to the National Health and Nutrition Examination Survey that was conducted between 1971–1975 reported in 2002 that high levels of sodium in the diet are an independent risk factor for congestive heart failure (CHF) in overweight adults. The authors of the study suggested that lowering the rate of sodium intake may play an important role in lowering the risk of CHF in overweight populations as well as individuals.

Another good reason for limiting one's intake of sodium is the link between high levels of dietary sodium and an increased risk of stomach cancer. This risk is increased if a person's diet is also low in fresh fruits and vegetables.

Apart from an increase in blood pressure, high levels of sodium may cause confusion, anxiety, edema, nausea, vomiting, restlessness, weakness, and loss of potassium and calcium.

People who are concerned about consuming too much sodium should try to keep their sodium intake below 2500 mg per day. This is the level recommended by the US Department of Health and Human Services and the US Department of Agriculture in their 2000 Dietary Guidelines for Americans. Ways to reduce sodium intake include the following:

• Reading the Nutrition Facts labels on processed food items. The amount of sodium in a specific processed food, such as cake mix or canned soup, can vary widely from brand to brand.
• Retraining the taste buds. A taste for salt is acquired. A gradual decrease in the use of salt to season foods gives the taste buds time to adjust.
• Using other spices and herbs to season food.
• Cooking from scratch rather than using processed foods.
• Substituting fresh fruits and vegetables for salty snack foods.
• Tasting food at the table before adding salt. Many people salt their food automatically before eating it, which often adds unnecessary sodium to the daily intake.
• Choosing foods that are labeled "low sodium" or "sodium free."
• Watching the sodium content of over-the-counter medications, and asking a pharmacist for information about the sodium content of prescription drugs.

Restricting sodium intake is not usually recommended for women who are pregnant or breast-feeding.

Side Effects

Dietary sodium is not associated with any bothersome or significant short-term side effects. In some people, however, salt tablets may cause upset stomach or affect kidney function.

Interactions

Sodium may promote the loss of calcium and potassium from the body. In addition, sodium in the diet should be restricted for such medications as antihypertensives (drugs to control blood pressure) and anticoagulants (blood thinners) to be fully effective.

Resources

Books

Pelletier, Kenneth R., MD. The Best Alternative Medicine, Part I: Food for Thought. New York: Simon & Schuster, 2002.

Sifton, David W. PDR Family Guide to Natural Medicines and Healing Therapies. New York: Three Rivers Press, 1999.

Periodicals

Becker, Elizabeth, and Marian Burros. "Eat Your Vegetables? Only at a Few Schools." New York Times, January 13, 2003.

He, J., L. G. Ogden, L. A. Bazzano, et al. "Dietary Sodium Intake and Incidence of Congestive Heart Failure in Overweight US Men and Women: First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study." Archives of Internal Medicine 162 (July 22, 2002): 1619-1624.

Ngoan, L. T., T. Mizoue, Y. Fujino, et al. "Dietary Factors and Stomach Cancer Mortality." British Journal of Cancer 87 (July 1, 2002): 37-42.

Nielsen, S. J., A. M. Siega-Riz, and B. M. Popkin. "Trends in Food Locations and Sources Among Adolescents and Young Adults." Preventive Medicine 35 (August 2002): 107-113.

Sukenik, S. "Balneotherapy for Rheumatic Diseases at the Dead Sea Area." Israeli Journal of Medicine and Science. (1996): S16–9.

Sukenik, S., D. Flusser, and S. Codish et al. "Balneotherapy at the Dead Sea Area for Knee Osteoarthritis." Israeli Journal of Medicine and Science. (1999):83–5.

Organizations

American Heart Association. 7272 Greenville Avenue, Dallas, TX 75231. http://www.americanheart.org/.

National Academy of Sciences. 500 Fifth Street, NW, Washington, DC 20001. .

[Article by: Greg Annussek; Rebecca J. Frey, PhD]

A metallic element that plays a major role in the regulation of the volume of water in the body. Deficiency is rare, but it can occur if losses from heavy sweating are not replaced. Deficiency leads to nausea, dizziness, and muscle cramps. An excessive intake of sodium (e.g. by eating too much table salt) has been linked with high blood pressure and heart disease.

Sodium is normally present in food and in the body in its ionic (charged) form rather than as metallic sodium. Sodium is a positively charged ion or cation (Na⁺), and it forms salts with a variety of negatively charged ions (anions). Table salt or sodium chloride (NaCl) is an example of a sodium salt. In solution, NaCl dissociates into its ions, Na⁺ and Cl^-. Other sodium salts include those of both inorganic (e.g., nitrite or bicarbonate) and organic anions (e.g., citrate or glutamate) in aqueous solution, these salts also dissociate into Na⁺ and the respective anion.

Types and Amounts of Common Foods That Contain the Recommended Levels of Sodium

Only small amounts of salt or sodium occur naturally in foods, but sodium salts are added to foods during food processing or during preparation as well as at the table. Most sodium is added to foods as sodium chloride (ordinary table salt), but small amounts of other salts such as sodium bicarbonate (baking soda and baking powder), monosodium glutamate, sodium sulfide, sodium nitrate, and sodium citrate are also added. Studies in a British population found that 75 percent of sodium intake came from salts added during manufacturing and processing, 15 percent from table salt added during cooking and at the table, and only 10 percent from natural foods (Sanchez-Castillo et al., 1987). Most sources of drinking water are low in sodium. However, the use of home water softening systems may greatly increase the sodium content of water; the system should be installed so that water for cooking and drinking bypasses the water softening system.

The estimated minimum safe daily intake of sodium for an adult (0.5 grams) can be obtained from ¼ teaspoon of salt, ¼ of a large dill pickle, ⅕ can of condensed tomato soup, one frankfurter, or fifteen potato chips. The effect of salt added in processing is noted by the calculation that, whereas one would need to consume 333 cups of fresh green peas (with no salt added during cooking or at the table) in order to consume 0.5 grams of sodium, the estimated minimum safe daily intake of sodium is provided by only 1.4 cups of canned or 2.9 cups of frozen green peas.

Whereas the estimated minimum safe intake for an adult is 0.5 g/day of sodium (1.3 g/day of sodium chloride), average Americans consume between 2 and 5 g/day of sodium (between 5 and 13 g/day of sodium chloride) (National Research Council, 1989). Sodium chloride, or salt, intake varies widely among cultures and among individuals. In Japan, where consumption of salt-preserved fish and the use of salt for seasoning are customary, salt intake is high, ranging from 14 to 20 g/day (Kono et al., 1983). On the other hand, the unacculturated Yanomamo Indians, who inhabit the tropical rain forest of northern Brazil and southern Venezuela, do not use salt in their diet and have an estimated sodium chloride intake of less than 0.3 g/day (Oliver et al., 1975). In the United States, individuals who consume diets high in processed foods tend to have high sodium chloride intakes, whereas vegetarians consuming unprocessed food may ingest less than 1 g/day of salt. Individuals with salt intakes less than 0.5 g/day do not normally exhibit chronic deficiencies, but appear to be able to regulate sodium chloride retention adequately.

Recommended Intake of Sodium

The daily minimum requirement of sodium for an adult is the amount needed to replace the obligatory loss of sodium. The minimum obligatory loss of sodium by an adult in the absence of profuse sweating or gastrointestinal or renal disease has been estimated to be approximately 115 mg/day, which is due to loss of about 23 mg/day in the urine and feces and of 46 to 92 mg/day through the skin (National Research Council, 1989). Because of large variations in the degrees of physical activity and in environmental conditions, the estimated level of safe minimum intake for a 70-kg adult was set at 500 mg/day of sodium (equivalent to 1,300 mg/day of sodium chloride) by the National Research Council (1989). Although there is no established optimal range of intake of sodium chloride, it is recommended that daily salt intake should not exceed 6 grams because of the association of high intake with hypertension (National Research Council, 1989). The Dietary Guidelines for Americans, published in 2000, include a recommendation to choose and prepare foods with less salt.

Individuals who wish to lower their sodium or salt intakes should use less salt at the table and during cooking, avoid salty foods such as potato chips, soy sauce, pickled foods, and cured meat, and avoid processed foods such as canned pasta sauces, canned vegetables, canned soups, crackers, bologna, and sausages. Individuals should also become aware of and avoid "hidden" sources of sodium such as softened water, products made with baking soda, and foods containing additives in the form of sodium salts.

The need for sodium chloride is increased during pregnancy and lactation, with the estimated safe minimum intake being increased by 69 mg/day and 135 mg/day, respectively, for women during pregnancy and lactation. The estimated minimum requirement for sodium is 120 mg/day for infants between birth and 5 months of age and 200 mg/day for infants 6 to 11 months of age (National Research Council, 1989); these intakes are easily met by human milk or infant formulas. The estimated minimum requirements of sodium for children range from 225 mg/day at one year of age to 500 mg/day at 10 to 18 years of age.

General Overview of Role of Sodium in Normal Physiology

Total body sodium has been estimated at 100 grams (4.3 moles) for a 70-kg adult. In general, the cytoplasm of cells is relatively rich in potassium (K>) and poor in sodium (Na>) and chloride (Cl<) ions. The concentrations of sodium (and potassium and chloride) ions in cells and the circulating fluids are held remarkably constant, and small deviations from normal levels in humans are associated with malfunction or disease. Na⁺, K⁺, and Cl^- are referred to as electrolytes because of their role in the generation of gradients and electrical potential differences across cell membranes. Sodium and sodium gradients across cell membranes play several important roles in the body. First, sodium gradients are important in many transport processes. Sodium tends to enter cells down its electrochemical gradient (toward the intracellular compartment that has a lower Na⁺ concentration and a more negative charge compared to the extracellular fluid compartment). This provides a secondary driving force for absorption of Cl^- in the same direction as Na⁺ movement or for the secretion of K⁺ or hydrogen ions (H⁺) in the opposite direction in exchange for Na⁺. The sodium gradient is also used to drive the coupled transport of Na⁺ and glucose, galactose, and amino acids by certain carrier proteins in cell membranes; because as Na⁺ enters down its electrochemical gradient, uptake of glucose/galactose or amino acids can occur against their concentration gradient. Second, sodium ions, along with potassium ions, play important roles in generating resting membrane potentials and in generating action potentials in nerve and muscle cells. Nerve and muscle cell membranes contain gated channels through which Na⁺ or K⁺ can flow. In the resting state, these cell membranes are highly impermeable to Na⁺ and permeable to K⁺ (i.e., Na⁺ channels are closed and K⁺ channels are open). These gated channels open or close in response to chemical messengers or to the traveling current (applied voltage). Action potentials are generated in nerve and muscle due to opening of Na⁺ channels followed by their closing and the re-opening of K⁺ channels.

A third important function of sodium is its osmotic role as a major determinant of extracellular fluid volume. The volume of the extracellular fluid compartment is determined primarily by the total amount of osmotic particles present. Because Na⁺, along with Cl^-, is the major determinant of osmolarity of extracellular fluid, disturbances in Na⁺ balance will change the volume of the extracellular fluid compartment. Finally, because Na⁺ is a fixed cation, it also plays a role in acid-base balance in the body. An excess of fixed cations (versus fixed anions) requires an increase in the concentration of bicarbonate ions.

Consequences of Deficiency or Excessive Intake Levels

Sodium balance in the body is well controlled via regulation of Na⁺ excretion by the kidneys. The kidneys respond to a deficiency of Na⁺ in the diet by decreasing its excretion, and they respond to an excess of Na⁺ by increasing its excretion in the urine. Physiological regulatory mechanisms for conservation of Na⁺ seem to be better developed in humans than mechanisms for excretion of Na⁺, and pathological states characterized by inappropriate retention of Na⁺ are more common than those characterized by Na⁺ deficiency.

Retention of Na⁺ occurs when Na⁺ intake exceeds the renal excretory capacity. This can occur with rapid ingestion of large amounts of salt (for example, ingestion of seawater) or with too-rapid intravenous infusion of saline. Hypernatremia (abnormally high plasma concentration of Na⁺) and hypervolemia (abnormally increased volume of blood), resulting in acute hypertension, usually occur in these situations, and the Na⁺ regulatory mechanisms will cause natriuresis (urinary excretion of Na⁺) and water retention.

The body may be depleted of Na⁺ under extreme conditions of heavy and persistent sweating or when conditions such as trauma, chronic vomiting or diarrhea, or renal disease produce an inability to retain Na⁺. Sodium depletion produces hyponatremia (abnormally low plasma concentration of Na⁺) and hypovolemia (abnormally decreased volume of blood) which place the individual at risk of shock. Medical treatment includes replacement of Na⁺ and water to restore the circulatory volume. If the loss of Na⁺ is not due to renal disease, mechanisms to conserve Na⁺ and water are activated. Loss of Na⁺ can also be caused by the administration of diuretics, which inhibit Na⁺ and Cl^- reabsorption, or by untreated diabetes mellitus, which causes diuresis.

Regulatory Processes That Govern the Uptake and Excretion of Sodium

The kidneys are the main site of regulation of Na⁺ balance. The intestines play a relatively minor role. Under normal circumstances, about 99 percent of dietary Na⁺ and Cl^- are absorbed, and the remainder is excreted in the feces. Absorption of Na⁺ and Cl^- occurs along the entire length of the intestines; 90 to 95 percent is absorbed in the small intestine and the rest in the colon. Intestinal absorption of Na⁺ and Cl^- is subject to regulation by the nervous system, hormones, and paracrine agonists released from neurons in the enteric nervous system in the wall of the intestines. The most important of these factors is aldosterone, a steroid hormone produced and secreted by the zona glomerulosa cells of the adrenal cortex. Aldosterone stimulates absorption of Na⁺ and secretion of K⁺, mainly by the colon and, to a lesser extent, by the ileum.

The kidneys respond to a deficiency of Na⁺ in the diet by decreasing its excretion, and they respond to an excess by increasing its excretion in the urine. Urinary loss of Na⁺ is controlled by varying the rate of Na⁺ reabsorption from the filtrate by renal tubular cells. Individuals consuming diets that are low in Na⁺ efficiently reabsorb Na⁺ from the renal filtrate and have low rates of excretion of Na⁺. When there is an excess of Na⁺ from high dietary intake, little Na⁺ is reabsorbed by renal tubular cells, resulting in the excretion of the excess Na⁺ in the urine. As much as 13 g/day of Na⁺ can be excreted in the urine.

The most important regulator of renal excretion of Na⁺ and Cl^- is the renin-angiotensin-aldosterone system (Laragh, 1985). Sensors in the nephrons of the kidney respond to changes in Na⁺ load by influencing the synthesis and secretion of renin (Levens et al., 1981). A decrease in renal perfusion or Na⁺ load will increase the release of renin. In the circulation, renin acts to initiate the formation of active angiotensin II from angiotensinogen, a protein produced by the liver. Angiotensin II conserves body Na⁺ by stimulating Na⁺ reabsorption by the renal tubules and indirectly via stimulating secretion of aldosterone. Secretion of aldosterone by the adrenal cortex is stimulated by a low plasma Na⁺ concentration and by angiotensin II. Aldosterone stimulates cells of the renal tubules to reabsorb Na⁺.

Because of the close association of Na⁺ and Cl^- concentrations with effective circulating volume, Na⁺ (and Cl^-) retention results in proportionate water retention, and Na⁺ (and Cl^-) loss results in proportionate water loss. Expansion or contraction of the extracellular volume affects the activation of vascular pressure receptors, as well as the release of natriuretic peptides by certain tissues, and result in changes, mediated largely by antidiuretic hormone (ADH), in renal excretion of Na⁺, Cl^-, and water. A deficiency of sodium chloride and hypovolemia have also been shown to produce an increase in appetite for salt, which will increase sodium chloride intake.

Evidence That Sodium Intake May Be Related to Risk of Hypertension

Both epidemiological and experimental studies implicate habitual high dietary salt intake in the development of hypertension (Weinberger, 1996). Primary hypertension, or abnormally high blood pressure, is a significant risk factor for cardiovascular disease, stroke, and renal failure in industrialized societies. Diets that are high in fat, high in sodium, low in potassium, low in calcium, and low in magnesium may contribute to the development of hypertension (Reusser and McCarron, 1994).

Although epidemiological and experimental evidence suggest a positive correlation between habitual high-salt consumption and hypertension, controversy remains regarding the importance of sodium salts in the regulation of blood pressure and the mechanisms by which salt influences blood pressure. This is not surprising, because the response of blood pressure depends on an interplay of various factors, such as genetic susceptibility, body mass, cardiovascular factors, regulatory mechanisms mediated through the neural and hormonal systems, and renal function.

A large comprehensive study on the role of sodium in hypertension was carried out in fifty-two geographically separate centers in thirty-two countries by the INTERSALT Cooperative Research Group (Stamler, 1997). Four centers included in the study had median values for Na⁺ excretion that were under 1.3 g/day. Subjects in these four unacculturated centers had low blood pressure, rare or absent hypertension, and no age-related rise in blood pressure as occurred in populations in the other forty-eight centers in which mean values for Na⁺ excretion were between 2.4 and 5.6 grams Na⁺ per day. Although blood pressure and sodium intake appeared to be associated when all fifty-two centers were included, the correlation between systolic blood pressure and excretion of sodium was not significant when the four centers with the lowest median values of sodium excretion were excluded from the analysis.

Intervention studies of dietary salt restriction to lower blood pressure have produced mixed results. This may be explained by the facts that not all hypertensive patients are salt-sensitive and that many cases of hypertension are due to other causes. Nevertheless, various clinical trials indicate some beneficial effects of dietary restriction of sodium on blood pressure (Cutler et al., 1997; Reusser and McCarron, 1994) with response being greater in older patients, patients with the highest degree of restriction, and in nonoverweight, mildly hypertensive patients.

Researchers are currently attempting to identify the genetic basis of salt-sensitive hypertension and to identify polymorphisms associated with salt-sensitive hypertensive individuals. More than thirty different gene variations could be responsible for essential hypertension, and hypertension is considered to have a complex genetic basis. Further insight into the basis of hypertension may help to determine individuals for whom lowering salt intake would be beneficial and to facilitate the prescription of appropriate drugs.

Brief Outline of the History of Salt

Common salt is the chemical compound NaCl. Salt makes up nearly 80 percent of the dissolved material in seawater and is also widely distributed in solid deposits. It is found in many evaporative deposits, where it crystallizes out of evaporating brine lakes, and in ancient bedrock, where large extinct salt lakes and seas evaporated millions of years ago. Salt was in general use long before history began to be recorded. Salt has been used widely for the curing, seasoning, and preserving of foods.

Bibliography

Church, Charles F., and Helen N.Church. Food Values of Portions Commonly Used: Bowes and Church. Philadelphia: J. B. Lippincott, 1970.

Cutler, Jeffrey A., Dean Follmann, and P. Scott Allender. "Randomized Trials of Sodium Reduction: An Overview." American Journal of Clinical Nutrition 65 (1997, Supp.): 643S–651S.

Kono, Suminori, Masato Ikeda, and Michiharu Ogata. "Salt and Geographical Mortality of Gastric Cancer and Stroke in Japan." Journal of Epidemiology and Community Health 37 (1983): 43–46.

Laragh, John H. "Atrial Natriuretic Hormone, the Renin-Aldosterone Axis, and Blood Pressure—Electrolyte Homeostasis." New England Journal of Medicine 313 (1985): 1330–1340.

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Oliver, Walter J., Erik L. Cohen, and James V. Neel. "Blood Pressure, Sodium Intake and Sodium-Related Hormones in the Yanomamo Indians, a 'No-Salt' Culture." Circulation 52 (1975): 146–151.

Reusser, Molly E., and David A. McCarron. "Micronutrient Effects on Blood Pressure Regulation." Nutrition Reviews 52 (1994): 367–375.

Sanchez-Castillo, C. P., S. Warrender, T. P. Whitehead, and W. P. James. "An Assessment of the Sources of Dietary Salt in a British Population." Clinical Science 72 (1987): 95–102.

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—Martha H. Stipanuk

A chemical element, atomic number 11, atomic weight 22.990, symbol Na. Sodium is the major cation of the extracellular fluid (ECF), constituting 90 to 95% of all cations in the blood plasma and interstitial fluid; it thus determines the osmolality of the ECF.

• s. acetate — a systemic and urinary alkalizer.
• s. acetylsalicylate — aspirin.
• s. acid phosphate, s. biphosphate — used as a dietary supplement of phosphorus for ruminants when only phosphorus is required and in small animals as a urinary acidifier.
• s. aminoarsonate — used as a feed additive to chickens and may cause arsenic poisoning if the dose rate is exceeded.
• s. antimony gluconate, s. stibogluconate — a pentavalent antimonial used in the treatment of leishmaniasis.
• s. arsanilate — used as a feed additive in the treatment of swine dysentery and in poultry and causes arsenic poisoning when dose rates are excessive.
• s. arsenite — used as a topical acaricide. See inorganic arsenic poisoning.
• s. arsenate — like the arsenite, a toxic compound used as an acaricide. Less toxic and less effective than the arsenite. See also inorganic arsenic poisoning.
• s. ascorbate — a form of ascorbic acid; vitamin C.
• s. azide — used in weed control and the prevention of rot in fruit; used in serum samples to prevent bacterial overgrowth.
• s. bentonite — see bentonite.
• s. benzoate — used topically as an antifungal agent in companion animals, with caffeine as a CNS stimulant and as a diagnostic aid in a liver function test.
• s. bicarbonate — a white powder found in most households in the form of baking soda; called also bicarbonate of soda. Used as a gastric antacid and as a systemic and urinary alkalinizer. See also milk shake. Used locally to remove mucus and to remove exudates and scabs.
• s. cacodylate — an organic compound yielding trivalent inorganic arsenic on metabolism in the body, similar in effects and toxicity to arsenic trioxide. Formerly used as a systemic treatment for chronic skin disease and capable of causing arsenic poisoning if used to excess.
• s.-calcium channels — see channel.
• s. carbonate — Na₂CO₃⋅H₂O, used as an alkalizing agent in pharmaceuticals, and has been used as a lotion or bath in the treatment of scaly skin, and as a detergent in companion animals.
• s. channels — see channel.
• s. chlorate — an oldfashioned herbicide which is quite palatable to farm animals and toxic in moderate amounts. Large doses cause abdominal pain, staggering and purging. Lower doses cause methemoglobinemia and dyspnea.
• s. chloride — salt; a necessary constituent of the body and therefore of the diet; sometimes used parenterally in solution to replenish electrolytes in the body.
• s. chloride nutritional deficiency — not a common occurrence but is seen in grazing animals on sodium deficient pastures, where heavy potash fertilizer has been applied in animals that are milking heavily, growing rapidly or losing a lot of sweat. Signs include pica, e.g. drinking urine, polydipsia, polyuria and decrease in appetite, milk yield, body weight, and urinary sodium and chloride.
• s. chloride poisoning (salt poisoning) — can occur via the diet due to accidental inclusion of too much salt; is usually too unpalatable. Most common is drinking of natural saline water from bore or deep well. Causes gastroenteritis, diarrhea and dehydration most noticeable in lactating animals. Animals are restless and play with water, looking for fresh water. Water contains also magnesium, sulfate and carbonate ions. If water intake restricted and salt intake normal a relative poisoning occurs. If combined with water deprivation causes polioencephalomalacia when the water intake returns to normal. In pigs the brain lesion is similar but because of the extensive infiltrations of eosinophils, characteristic of pigs, it is called eosinophilic meningoencephalitis.
• s. chloroacetate — a herbicide with very low toxicity potential.
• s. citrate — an alkalinizing agent; used also as an in vitro anticoagulant in blood stored for transfusion or diagnostic use.
• s. cyanide — a highly toxic industrial chemical and unlikely to enter the animal food chain unless as a result of a spill of reagents or industrial waste.
• s. diethyldithiocarbamate — a chelating agent used in the treatment for thallium poisoning; also used as an immunomodulator in the treatment of human immunodeficiency virus infection in humans.
• s. fluoride — a white, odorless powder used at one time for the treatment of ascariasis in pigs. Has no use in veterinary medicine comparable to its use as a prophylactic against dental caries in humans. See also fluorosis.
• s. fluoroacetamide — 1081; causes poisoning similar to sodium fluoroacetate (below).
• s. fluoroacetate — occurs naturally in some plants and used in agriculture as a rodenticide known as 1080. The latter is a restricted substance and is only sold on license. Two forms of poisoning occur: (1) myocardial failure resulting in sudden death in herbivora; signs are dyspnea, cardiac irregularity; (2) excitement and convulsions in pigs and dogs. Both poisonings are highly fatal. Plants containing fluoroacetate are Gastrolobium spp., Acacia georgina (gidgee), Dichapetalum spp., Palicourea spp.
• s. fluorosilicate — is used as an insecticide in bait form for crickets and grasshoppers and as an insecticide dust for poultry. It is as toxic as sodium fluoride.
• s. glutamate — the monosodium salt of l-glutamic acid; used in treatment of encephalopathies associated with liver diseases. Also used to enhance the flavor of foods.
• s. homeostasis — maintenance of the body's sodium status at an appropriate level; effected principally by aldosterone increasing tubular resorption of sodium from the glomerular filtrate.
• s. hyaluronate — used in the treatment of degenerative joint disease in horses. See also hyaluronic acid.
• s. hydroxide — an all-purpose caustic. Its biggest use in veterinary science is to clean down fat-laden surfaces in abattoirs prior to disinfection.
• s. hypochlorite — a compound having germicidal, deodorizing and bleaching properties; used in solution to disinfect utensils, and in diluted form (Dakin's solution) as a local antibacterial and to irrigate wounds. A common disinfectant for a wide variety of uses in veterinary medicine, including application to cow's teats in mastitis control programs. Called also bleach.
• s. iodide — a compound used as a source of iodine and as an expectorant. At times used parenterally in the treatment of extensive ringworm, actinobacillosis and actinomycosis. Overuse causes iodism.
• s. lactate — a compound used in solution to replenish body fluids and electrolytes.
• s. lauryl sulfate — an anionic surface-active agent used in shampoos as a detergent and wetting agent to increase skin penetration of active ingredients.
• s. metabisulfite — used as an antioxidant and as an aid in the making of ensilage. Also used as a preservative on meat, as a source of sulfur dioxide.
• s. methanearsonate — a herbicide—monosodium acid methanearsonate—causes arsenic poisoning.
• s. molybdate — used in salt mixture and as pasture topdressing as a prophylaxis against chronic copper poisoning in ruminants.
• s. monofluoroacetate — see sodium fluoroacetate (above).
• s. nitrate — used in food preservation especially meat pickling and as a fertilizer. Can cause nitrate–nitrite poisoning or nitrite poisoning in ruminants.
• s. nitrite — a vasodilator; used in the treatment of cyanide poisoning. Can cause methemoglobinemia and death from anoxia.
• s. oleate — used by local injection in horses to cause inflammation and aid healing of chronic injuries such as splints and bucked shins.
• s. oxalate — see soluble oxalate poisoning.
• s. pentachlorophenate — used as a fungicide in wood preservatives. Acute poisoning after heavy dosing causes dyspnea and death due to respiratory failure.
• s. perborate — an oxidizing agent; used as a topical antiseptic and mouthwash.
• s. phosphate — an osmotic cathartic.
• s.-potassium-ATPase pump — see pump.
• s.-potassium channels — see channel.
• s./potassium ratio — a low ratio, indicating hyponatremia and hyperkalemia, is characteristic of hypoadrenocorticism.
• s. propionate — used in the prophylaxis and treatment of acetonemia in cows, and as a fungistat both topically and in preparations for animal medication.
• s. pump — see sodium pump.
• s.-restricted diets — used in the dietary management of heart disease and hypertension in dogs and cats.
• s. salicylate — an analgesic, antipyretic compound. See salicylate.
• s. selenite — used as treatment for severe nutritional deficiency of selenium. Overdose will cause poisoning by selenium.
• s. sulfanilate — rate of excretion is used as a sensitive test of urinary function. See also sulfanilate.
• s. sulfate — an osmotic cathartic; also used as a diuretic and sometimes applied topically in solution to relieve edema and pain of infected wounds. Called also Glauber's salts.
• s. sulfite test — 1. precipitates protein out of solution; a dramatic test for protein in urine.
— 2. a turbidity test on serum for proximate estimation of gamma globulin content and immunological status of newborn calf.
• s. tetraborate — called also borax; used as a weak disinfectant.
• s. thiosulfate — a compound used in the treatment of cyanide poisoning, and used in measuring the volume of extracellular body fluid and the renal glomerular filtration rate.
• s. trichloroacetate — a nontoxic herbicide.
• s. versenate — see edetate.

neon ← sodium → magnesium Li ↑ Na ↓ K 11Na Periodic table
Appearance
silvery white metallic
General properties
Name, symbol, number	sodium, Na, 11
Element category	alkali metal
Group, period, block	1, 3, s
Standard atomic weight	22.98976928(2) g·mol−1
Electron configuration	[Ne] 3s1
Electrons per shell	2,8,1 (Image)
Physical properties
Phase	solid
Density (near r.t.)	0.968 g·cm−3
Liquid density at m.p.	0.927 g·cm−3
Melting point	370.87 K, 97.72 °C, 207.9 °F
Boiling point	1156 K, 883 °C, 1621 °F
Critical point	(extrapolated) 2573 K, 35 MPa
Heat of fusion	2.60 kJ·mol−1
Heat of vaporization	97.42 kJ·mol−1
Specific heat capacity	(25 °C) 28.230 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k at T/K 554 617 697 802 946 1153
Atomic properties
Oxidation states	+1, -1 (strongly basic oxide)
Electronegativity	0.93 (Pauling scale)
Ionization energies (more)	1st: 495.8 kJ·mol−1
	2nd: 4562 kJ·mol−1
	3rd: 6910.3 kJ·mol−1
Atomic radius	186 pm
Covalent radius	166±9 pm
Van der Waals radius	227 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 47.7 nΩ·m
Thermal conductivity	(300 K) 142 W·m−1·K−1
Thermal expansion	(25 °C) 71 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 3200 m/s
Young's modulus	10 GPa
Shear modulus	3.3 GPa
Bulk modulus	6.3 GPa
Mohs hardness	0.5
Brinell hardness	0.69 MPa
CAS registry number	7440-23-5
Most stable isotopes
Main article: Isotopes of sodium
iso NA half-life DM DE (MeV) DP 22Na trace 2.602 y β+→γ 0.5454 22Ne* 1.27453(2)[1] 22Ne ε→γ - 22Ne* 1.27453(2) 22Ne β+ 1.8200 22Ne 23Na 100% 23Na is stable with 12 neutrons
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Sodium (pronounced /ˈsoʊdiəm/, SOH-di-əm) is a metallic element with a symbol Na (from Latin natrium or Arabic natrun) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1" (formerly known as ‘group IA’). It has only one stable isotope, ²³Na.

Elemental sodium was first isolated by Sir Humphry Davy in 1806 by passing an electric current through molten sodium hydroxide. Elemental sodium does not occur naturally on Earth, but quickly oxidizes in air and is violently reactive with water, so it must be stored in an inert medium, such as a liquid hydrocarbon. The free metal is used for some chemical synthesis, analysis, and heat transfer applications.

Sodium ion is soluble in water in nearly all of its compounds, and is thus present in great quantities in the Earth's oceans and other stagnant bodies of water. In these bodies it is mostly counterbalanced by the chloride ion, causing evaporated ocean water solids to consist mostly of sodium chloride, or common table salt. Sodium ion is also a component of many minerals.

Sodium is an essential element for all animal life and for some plant species. In animals, sodium ions are used in opposition to potassium ions, to allow the organism to build up an electrostatic charge on cell membranes, and thus allow transmission of nerve impulses when the charge is allowed to dissipate by a moving wave of voltage change. Sodium is thus classified as a “dietary inorganic macro-mineral” for animals. Sodium's relative rarity on land is due to its solubility in water, thus causing it to be leached into bodies of long-standing water by rainfall. Such is its relatively large requirement in animals, in contrast to its relative scarcity in many inland soils, that herbivorous land animals have developed a special taste receptor for sodium ion.

Contents 1 Characteristics 1.1 Chemical properties 1.2 Compounds 1.3 Spectroscopy 1.4 Isotopes 2 History 3 Occurrence 4 Commercial production 5 Applications 5.1 Metallic sodium 5.2 Sodium compounds 6 Nuclear Reactor Cooling 7 Biological role 7.1 Maintaining body fluid volume in animals 7.2 Maintaining electric potential in animal tissues 8 Dietary uses 9 Precautions 10 See also 11 References 12 External links

Characteristics

At room temperature, sodium metal is soft enough that it can be cut with a knife. In air, the bright silvery luster of freshly exposed sodium will rapidly tarnish. The density of alkali metals generally increases with increasing atomic number, but sodium is denser than potassium. Sodium is a fairly good conductor of heat.

Chemical properties

Sodium metal (ca. 10 g) under oil

Compared with other alkali metals, sodium is generally less reactive than potassium and more reactive than lithium,^[2] in accordance with "periodic law": for example, their reaction in water, chlorine gas, etc.

Sodium reacts exothermically with water: small pea-sized pieces will bounce across the surface of the water until they are consumed by it, whereas large pieces will explode. While sodium reacts with water at room temperature, the sodium piece melts with the heat of the reaction to form a sphere, if the reacting sodium piece is large enough. The reaction with water produces very caustic sodium hydroxide (lye) and highly flammable hydrogen gas. These are extreme hazards (see Precautions section below). When burned in air, sodium forms sodium peroxide Na₂O₂, or with limited oxygen, the oxide Na₂O (unlike lithium, the nitride is not formed). If burned in oxygen under pressure, sodium superoxide NaO₂ will be produced.

Compounds

See also: Category:Sodium compounds

Sodium tends to form water-soluble compounds, such as halides, sulfate, nitrate, carboxylates and carbonates. There are only isolated examples of sodium compounds precipitating from water solution. However, nature provides examples of many insoluble sodium compounds such as the feldspars (aluminum silicates of sodium, potassium and calcium). There are other insoluble sodium salts such as sodium bismuthate NaBiO₃, sodium octamolybdate Na₂Mo₈O₂₅• 4H₂O, sodium thioplatinate Na₄Pt₃S₆, sodium uranate Na₂UO₄. Sodium meta-antimonate's 2NaSbO₃•7H₂O solubility is 0.3 g/L as is the pyro form Na₂H₂Sb₂O₇•H₂O of this salt. Sodium metaphosphate NaPO₃ has a soluble and an insoluble form.^[3]

Sodium compounds are important to the chemical, glass, metal, paper, petroleum, soap, and textile industries. Hard soaps are generally sodium salt of certain fatty acids (potassium produces softer or liquid soaps).^[4]

The sodium compounds that are the most important to industries are common salt (NaCl), soda ash (Na₂CO₃), baking soda (NaHCO₃), caustic soda (NaOH), sodium nitrate (NaNO₃), di- and tri-sodium phosphates, sodium thiosulfate (hypo, Na₂S₂O₃ · 5H₂O), and borax (Na₂B₄O₇·10H₂O).^[4]

Spectroscopy

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Sodium spectral lines.

A low pressure sodium/sodium oxide (LPS/SOX) streetlamp at full power (detail)

A FASOR tuned to the D2A component of the sodium D line, used at the Starfire Optical Range to excite sodium atoms in the upper atmosphere.

When sodium or its compounds are introduced into a flame, they turn the flame a bright yellow color.

One notable atomic spectral line of sodium vapor is the so-called D-line, which may be observed directly as the sodium flame-test line (see Applications) and also the major light output of low-pressure sodium lamps (these produce an unnatural yellow, rather than the peach-colored glow of high pressure lamps). The D-line is one of the classified Fraunhofer lines observed in the visible spectrum of the Sun's electromagnetic radiation. Sodium vapor in the upper layers of the Sun creates a dark line in the emitted spectrum of electromagnetic radiation by absorbing visible light in a band of wavelengths around 589.5 nm. This wavelength corresponds to transitions in atomic sodium in which the valence-electron transitions from a 3p to 3s electronic state. Closer examination of the visible spectrum of atomic sodium reveals that the D-line actually consists of two lines called the D₁ and D₂ lines at 589.6 nm and 589.0 nm, respectively. This fine structure results from a spin-orbit interaction of the valence electron in the 3p electronic state. The spin-orbit interaction couples the spin angular momentum and orbital angular momentum of a 3p electron to form two states that are respectively notated as 3p(²P01/2) and 3p(²P03/2) in the LS coupling scheme. The 3s state of the electron gives rise to a single state which is notated as 3s(²S_1/2) in the LS coupling scheme. The D₁-line results from an electronic transition between 3s(²S_1/2) lower state and 3p(²P01/2) upper state. The D₂-line results from an electronic transition between 3s(²S_1/2) lower state and 3p(²P03/2) upper state. Even closer examination of the visible spectrum of atomic sodium would reveal that the D-line actually consists of a lot more than two lines. These lines are associated with hyperfine structure of the 3p upper states and 3s lower states. Many different transitions involving visible light near 589.5 nm may occur between the different upper and lower hyperfine levels.^[5][6]

A practical use for lasers which work at the sodium D-line transition (see FASOR illustration) is to create artificial laser guide stars (artificial star-like images from sodium in the upper atmosphere) which assist in the adaptive optics for large land-based visible light telescopes.

Isotopes

Main article: Isotopes of sodium

Thirteen isotopes of sodium have been recognized. The only stable isotope is ²³Na. Sodium has two radioactive cosmogenic isotopes which are also the two isotopes with longest half life, ²²Na, with a half-life of 2.6 years and ²⁴Na with a half-life of 15 hours. All other isotopes have a half life of less than one minute.^[7]

Acute neutron radiation exposure (e.g., from a nuclear criticality accident) converts some of the stable ²³Na in human blood plasma to ²⁴Na. By measuring the concentration of this isotope, the neutron radiation dosage to the victim can be computed.^[8]

History

The flame test for sodium displays a brilliantly bright yellow emission due to the so called "sodium D-lines" at 588.9950 and 589.5924 nanometers.

Salt has been an important commodity in human activities, as testified by the English word salary, referring to 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 probably originates from the Arabic word suda meaning headache as the headache-alleviating properties of sodium carbonate or soda were well known in early times.^[9]

Sodium's chemical abbreviation Na was first published by Jöns Jakob Berzelius in his system of atomic symbols (Thomas Thomson, Annals of Philosophy^[10]) and is a contraction of the element's new Latin name natrium which refers to the Egyptian natron,^[9] the word for a natural mineral salt whose primary ingredient is hydrated sodium carbonate. Hydrated sodium carbonate historically had several important industrial and household uses later eclipsed by soda ash, baking soda and other sodium compounds.

Although sodium (sometimes called "soda" in English) has long been recognized in compounds, it was not isolated until 1807 by Sir Humphry Davy through the electrolysis of caustic soda.^[11]

Sodium imparts an intense yellow color to flames. As early as 1860, Kirchhoff and Bunsen noted the high sensitivity that a flame test for sodium could give. They state in Annalen der Physik und Chemie in the paper "Chemical Analysis by Observation of Spectra":

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

Albite (NaAlSi₃O₈), a sodium-containing mineral.

See also: Category:Sodium minerals

Owing to its high reactivity, sodium is found in nature only as a compound and never as the free element. Sodium makes up about 2.6% by weight of the Earth's crust, making it the sixth most abundant element overall^[12] and the most abundant alkali metal. Sodium is found in many different minerals, of which the most common is ordinary salt (sodium chloride), which occurs in vast quantities dissolved in seawater, as well as in solid deposits (halite). Others include amphibole, cryolite, soda niter and zeolite.

Sodium is relatively abundant in stars and the D spectral lines of this element are among the most prominent in star light. Though elemental sodium has a rather high vaporization temperature, its relatively high abundance and very intense spectral lines have allowed its presence to be detected by ground telescopes and confirmed by spacecraft (Mariner 10 and MESSENGER) in the thin atmosphere of the planet Mercury.^[13]

Commercial production

Sodium was first produced commercially in 1855 by thermal reduction of sodium carbonate with carbon at 1100 °C, in what is known as the Deville process.^[14]

Na₂CO₃ (liquid) + 2 C (solid) → 2 Na (vapor) + 3 CO (gas).

A process based on the reduction of sodium hydroxide was developed in 1886.^[14]

Sodium is now produced commercially through the electrolysis of liquid sodium chloride, based on a process patented in 1924.^[15][16] 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 formed at the anode. This method is less expensive than the previous Castner process of electrolyzing sodium hydroxide.

Very pure sodium can be isolated by the thermal decomposition of sodium azide.^[17]

Sodium metal in reagent-grade sold for about $1.50/pound ($3.30/kg) in 2009 when purchased in tonnage quantities. Lower purity metal sells for considerably less. The market in this metal is volatile due to the difficulty in its storage and shipping. It must be stored under an dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of sodium oxide or sodium superoxide. These oxides can react violently in the presence of organic materials. Sodium will also burn violently when heated in air. ^[18]

Kilogram quantities of sodium cost far more, in the range of $165/kg. This is partially due to the cost of shipping hazardous material. ^[19]

Applications

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Metallic sodium

• Sodium in its metallic form can be used to refine some reactive metals, such as zirconium and potassium, from their compounds.
• In certain alloys to improve their structure.
• To descale metal (make its surface smooth).
• To purify molten metals.
• In sodium vapor lamps, an efficient means of producing light from electricity (see the picture), often used for street lighting in cities. Low-pressure sodium lamps give a distinctive yellow-orange light which consists primarily of the twin sodium D lines. High-pressure sodium lamps give a more natural peach-colored light, composed of wavelengths spread much more widely across the spectrum.
• As a heat transfer fluid in some types of nuclear reactors and inside the hollow valves of high-performance internal combustion engines.
• In organic synthesis, sodium is used as a reducing agent, for example in the Birch reduction.
• In chemistry, sodium is often used either alone or with potassium in an alloy, NaK as a desiccant for drying solvents. Used with benzophenone, it forms an intense blue coloration when the solvent is dry and oxygen-free.
• The sodium fusion test uses sodium's high reactivity, low melting point, and the near-universal solubility of its compounds, to qualitatively analyze compounds.

Sodium compounds

• This alkali metal as the Na⁺ ion is vital to animal life.
• In soap, as sodium salts of fatty acids. Sodium soaps are harder (higher melting) soaps than potassium soaps.
• In some medicine formulations, the salt form of the active ingredient usually with sodium or potassium is a common modification to improve bioavailability.
• Sodium chloride (NaCl), a compound of sodium ions and chloride ions, is an important heat transfer material.

Nuclear Reactor Cooling

Molten sodium is used as a coolant in some types of nuclear reactors. In 1995 nearly three tons of sodium leaked from the fast breeder reactor in Monju Japan and caught fire. There have been many other such leaks around the world. Since sodium melts at about 98 °C, cooling pipes using it can freeze up when the reactor is shut down.

Where reactors need to be frequently shut down, the alloy of sodium and potassium called NaK is used. It melts at -11 Cº so cooling pipes will not freeze up at room temperature. Nak is more dangerous than pure sodium in case of leaks because of the presence of potassium.

Biological role

Maintaining body fluid volume in animals

Main articles: Renin-angiotensin system and atrial natriuretic peptide

The serum sodium and urine sodium play important roles in medicine, both in the maintenance of sodium and total body fluid homeostasis, and in the diagnosis of disorders causing homeostatic disruption of salt/sodium and water balance.

In mammals, decreases in blood pressure and decreases in sodium concentration sensed within the kidney result in the production of renin, a hormone which acts in a number of ways, one of them being to act indirectly to cause the generation of aldosterone, a hormone which decreases the excretion of sodium in the urine. As the body of the mammal retains more sodium, other osmoregulation systems which sense osmotic pressure in part from the concentration of sodium and water in the blood, act to generate antidiuretic hormone. This, in turn, which causes the body to retain water, thus helping to restore the body's total amount of fluid.

There is also a counterbalancing system, which senses volume. As fluid is retained, receptors in the heart and vessels which sense distension and pressure, cause production of atrial natriuretic peptide, which is named in part for the Latin word for sodium. This hormone acts in various ways to cause the body to lose sodium in the urine. This causes the body's osmotic balance to drop (as low concentration of sodium is sensed directly), which in turn causes the osmoregulation system to excrete the "excess" water. The net effect is to return the body's total fluid levels back toward normal.

Maintaining electric potential in animal tissues

Main article: Action potential

Sodium cations are important in neuron (brain and nerve) function, and in influencing osmotic balance between cells and the interstitial fluid, with their distribution mediated in all animals (but not in all plants) by the so-called Na⁺/K⁺-ATPase pump.^[20] Sodium is the chief cation in fluid residing outside cells in the mammalian body (the so-called extracellular compartment), with relatively little sodium residing inside cells. The volume of extracellular fluid is typically 15 liters in a 70 kg human, and the 50 grams of sodium it contains is about 90% of the body's total sodium content.

Dietary uses

The most common sodium salt, sodium chloride ('table salt' or 'common salt'), is used for seasoning and warm-climate food preservation, such as pickling and making jerky (the high osmotic content of salt inhibits bacterial and fungal growth). The human requirement for sodium in the diet is about 500 mg per day,^[21] which is typically less than a tenth as much as many diets "seasoned to taste." Most people consume far more sodium than is physiologically needed. For certain people with salt-sensitive blood pressure, this extra intake may cause a harmful effect on health. However, low sodium intake may lead to sodium deficiency (hyponatremia).

Precautions

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Extreme care is required in handling elemental/metallic sodium. Sodium is potentially explosive in water (depending on quantity), and it is rapidly converted to sodium hydroxide on contact with moisture and sodium hydroxide is a corrosive substance. The powdered form may combust spontaneously in air or oxygen. Sodium must be stored either in an inert (oxygen and moisture free) atmosphere (such as nitrogen or argon), or under a liquid hydrocarbon such as mineral oil or kerosene.

The reaction of sodium and water is a familiar one in chemistry labs, and is reasonably safe if amounts of sodium smaller than a pencil eraser are used and the reaction is done behind a plastic shield by people wearing eye protection. However, the sodium-water reaction does not scale up well, and is treacherous when larger amounts of sodium are used. Larger pieces of sodium melt under the heat of the reaction, and the molten ball of metal is buoyed up by hydrogen and may appear to be stably reacting with water, until splashing covers more of the reaction mass, causing thermal runaway and an explosion which scatters molten sodium, lye solution, and sometimes flame. (18.5 g explosion [1]) This behavior is unpredictable, and among the alkali metals it is usually sodium which invites this surprise phenomenon, because lithium is not reactive enough to do it, and potassium is so reactive that chemistry students are not tempted to try the reaction with larger potassium pieces.

Sodium is much more reactive than magnesium; a reactivity which can be further enhanced due to sodium's much lower melting point. When sodium catches fire in air (as opposed to just the hydrogen gas generated from water by means of its reaction with sodium) it more easily produces temperatures high enough to melt the sodium, exposing more of its surface to the air and spreading the fire.

Few common fire extinguishers work on sodium fires. Water, of course, exacerbates sodium fires, as do water-based foams. CO₂ and Halon are often ineffective on sodium fires, which reignite when the extinguisher dissipates. Among the very few materials effective on a sodium fire are Pyromet and Met-L-X. Pyromet is a NaCl/(NH₄)₂HPO₄ mix, with flow/anti-clump agents. It smothers the fire, drains away heat, and melts to form an impermeable crust. This is the standard dry-powder canister fire extinguisher for all classes of fires. Met-L-X is mostly sodium chloride, NaCl, with approximately 5% Saran plastic as a crust-former, and flow/anti-clumping agents. It is most commonly hand-applied, with a scoop. Other extreme fire extinguishing materials include Lith+, a graphite based dry powder with an organophosphate flame retardant; and Na+, a Na₂CO₃-based material.

Because of the reaction scale problems discussed above, disposing of large quantities of sodium (more than 10 to 100 grams) must be done through a licensed hazardous materials disposer. Smaller quantities may be broken up and neutralized carefully with ethanol (which has a much slower reaction than water), or even methanol (where the reaction is more rapid than ethanol's but still less than in water), but care should nevertheless be taken, as the caustic products from the ethanol or methanol reaction are just as hazardous to eyes and skin as those from water. After the alcohol reaction appears complete, and all pieces of reaction debris have been broken up or dissolved, a mixture of alcohol and water, then pure water, may then be carefully used for a final cleaning. This should be allowed to stand a few minutes until the reaction products are diluted more thoroughly and flushed down the drain. The purpose of the final water soaking and washing of any reaction mass or container which may contain sodium, is to ensure that alcohol does not carry unreacted sodium into the sink trap, where a water reaction may generate hydrogen in the trap space which can then be potentially ignited, causing a confined sink trap explosion.

See also

• Alkali metals
• Sodium compounds

References

1. ^ Endt, P. M. ENDT, ,1 (1990) (12/1990). "Energy levels of A = 21-44 nuclei (VII)". Nuclear Physics A 521: 1. doi:10.1016/0375-9474(90)90598-G. 
2. ^ De Leon, N.. "Reactivity of Alkali Metals". Indiana University Northwest. http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/alkali-reac.html. Retrieved 2007-12-07. 
3. ^ Dean, John Aurie; Lange, Norbert Adolph (1998). Lange's Handbook of Chemistry. McGraw-Hill. ISBN 0070163847. 
4. ^ ^{a b} Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils; (1985). "Natrium" (in German). Lehrbuch der Anorganischen Chemie (91–100 ed.). Walter de Gruyter. pp. 931–943. ISBN 3-11-007511-3. 
5. ^ Citron, M. L., et al. (1977). "Experimental study of power broadening in a two level atom". Physical Review A 16: 1507. doi:10.1103/PhysRevA.16.1507. http://prola.aps.org/abstract/PRA/v16/i4/p1507_1. 
6. ^ Steck, Daniel A.. "Sodium D. Line Data" (PDF). Los Alamos National Laboratory (technical report). http://george.ph.utexas.edu/~dsteck/alkalidata/sodiumnumbers.pdf. 
7. ^ Audi, Georges (2003). "The NUBASE Evaluation of Nuclear and Decay Properties". Nuclear Physics A (Atomic Mass Data Center) 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001. 
8. ^ Sanders, F. W.; Auxier, J. A. (1962). "Neutron Activation of Sodium in Anthropomorphous Phantoms". Health Physics 8 (4): 371–379. doi:10.1097/00004032-196208000-00005. http://www.health-physics.com/pt/re/healthphys/abstract.00004032-196208000-00005.htm. 
9. ^ ^{a b} Newton, David E.. Chemical Elements. ISBN 0-7876-2847-6. 
10. ^ van der Krogt, Peter. "Elementymology & Elements Multidict". http://www.vanderkrogt.net/elements/elem/na.html. Retrieved 2007-06-08. 
11. ^ Davy, Humphry (1808). "On some new Phenomena of Chemical Changes produced by Electricity, particularly the Decomposition of the fixed Alkalies, and the Exhibition of the new Substances, which constitute their Bases". Philosophical Transactions of the Royal Society of London 98: 1–45. doi:10.1098/rstl.1808.0001. http://books.google.com/books?id=Kg9GAAAAMAAJ. 
12. ^ Lide, D. R., ed. (2005), CRC Handbook of Chemistry and Physics (86th ed.), Boca Raton (FL): CRC Press, ISBN 0-8493-0486-5 
13. ^ "Sodium found in Mercury's atmosphere". BNET. 1985-08-17. http://findarticles.com/p/articles/mi_m1200/is_v128/ai_3898126. Retrieved 2008-09-18. 
14. ^ ^{a b} Eggeman, Tim. Sodium and Sodium Alloys. Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. Published online 2007. doi:10.1002/0471238961.1915040912051311.a01.pub2
15. ^ Pauling, Linus, General Chemistry, 1970 ed., Dover Publications
16. ^ "Los Alamos National Laboratory – Sodium". http://periodic.lanl.gov/elements/11.html. Retrieved 2007-06-08. 
17. ^ Merck Index, 9th ed., monograph 8325
18. ^ Sodium Metal 99.97% Purity
19. ^ 007-Sodium Metal
20. ^ Campbell, Neil (1987). Biology. Menlo Park, Calif.: Benjamin/Cummings Pub. Co.. pp. 795. ISBN 0-8053-1840-2. 
21. ^ National Heart, Lung, and Blood Institute (1996). Implementing recommendations for dietary salt reduction: Where are we?. DIANE Publishing. p. 10. ISBN 1428929096. http://books.google.com/books?id=U2JA_A8OK68C&pg=PT10. 

External links

Wikimedia Commons has media related to: Sodium

Look up sodium in Wiktionary, the free dictionary.

• The Periodic Table of Videos - Sodium
• Etymology of "natrium" - source of symbol Na
• WebElements.com – Sodium
• The Wooden Periodic Table Table's Entry on Sodium
• Dietary Sodium
• Sodium isotopes data from The Berkeley Laboratory Isotopes Project's

v • d • e Periodic table
H																															He
Li	Be																									B	C	N	O	F	Ne
Na	Mg																									Al	Si	P	S	Cl	Ar
K	Ca	Sc															Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y															Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Uuq	Uup	Uuh	Uus	Uuo
Uue	Ubn
Alkali metals Alkaline earth metals Lanthanoids Actinoids Transition metals Other metals Metalloids Other nonmetals Halogens Noble gases

v • d • e   Sodium compounds NaAlO2 · NaBH3(CN) · NaBH4 · NaBr · NaBrO4 · NaCH3COO · NaCN · NaC6H5CO2 · NaCl · NaClO · NaClO2 · NaClO3 · NaClO4 · NaF · NaH · NaHCO3 · NaHSO3 · NaHSO4 · NaI · NaIO3 · NaIO4 · NaMnO4 · NaNH2 · NaNO2 · NaNO3 · NaN3 · NaOH · NaO2 · NaPO2H2 · NaReO4 · NaSCN · NaSH · NaTcO4 · NaVO3 · Na2CO3 · Na2C2O4 · Na2CrO4 · Na2Cr2O7 · Na2MnO4 · Na2MoO4 · Na2O · Na2O2 · Na2O(UO3)2 · Na2S · Na2SO3 · Na2SO4 · Na2S2O3 · Na2S2O4 · Na2S2O5 · Na2S2O6 · Na2S2O7 · Na2S2O8 · Na2SeO3 · Na2SeO4 · Na2SiO3 · Na2Te · Na2TeO3 · Na2Ti3O7 · Na2U2O7 · NaWO4 · Na2Zn(OH)4 · Na3N · Na3P · Na3VO4 · Na4Fe(CN)6  · Na5P3O10

v • d • e Alkali metals     Lithium Li Atomic Number: 3 Atomic Weight: 6.941 Melting Point: 453.69 K Boiling Point: 1615 K Specific mass: 0.534 g/cm3 Electronegativity: 0.98 Sodium Na Atomic Number: 11 Atomic Weight: 22.990 Melting Point: 370.87 K Boiling Point: 1156 K Specific mass: 0.97 g/cm3 Electronegativity: 0.96 Potassium K Atomic Number: 19 Atomic Weight: 39.098 Melting Point: 336.58 K Boiling Point: 1032 K Specific mass: 0.86 g/cm3 Electronegativity: 0.82 Rubidium Rb Atomic Number: 37 Atomic Weight: 85.468 Melting Point: 312.46 K Boiling Point: 961 K Specific mass: 1.53 g/cm3 Electronegativity: 0.82 Caesium Cs Atomic Number: 55 Atomic Weight: 132.905 Melting Point: 301.59 K Boiling Point: 944 K Specific mass: 1.93 g/cm3 Electronegativity: 0.79 Francium Fr Atomic Number: 87 Atomic Weight: (223) Melting Point: 295(?) K Boiling Point: 950(?) K Specific mass: ? g/cm3 Electronegativity: 0.7

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Dansk (Danish)
n. - natrium

idioms:

• sodium bicarbonate    natriumbikarbonat, tvekulsurt natron
• sodium carbonate    natriumkarbonat, kulsurt natron
• sodium chloride    natriumklorid, kogsalt
• sodium hydroxide    natriumhydroxyd
• sodium lamp    natriumlampe
• sodium nitrate    natriumnitrat, salpetersurt natron
• sodium-vapour lamp    natriumdamplampe

Nederlands (Dutch)
natrium

Français (French)
n. - sodium, soude

idioms:

• sodium bicarbonate    bicarbonate de soude
• sodium carbonate    carbonate de sodium
• sodium chloride    chlorure de sodium
• sodium hydroxide    hydroxyde de sodium
• sodium lamp    lampe/ampoule au sodium
• sodium nitrate    nitrate de sodium
• sodium-vapour lamp    lampe à vapeur de sodium

Deutsch (German)
n. - Natrium

idioms:

• sodium bicarbonate    doppeltkohlensaures Natrium
• sodium carbonate    Natriumkarbonat
• sodium chloride    Natriumchlorid
• sodium hydroxide    Ätznatron
• sodium lamp    Natriumdampflampe
• sodium nitrate    Natriumnitrat
• sodium-vapour lamp    Natriumdampflampe

Ελληνική (Greek)
n. - (χημ.) νάτριο

idioms:

• sodium bicarbonate    (χημ.) διττανθρακικό νάτρι, σόδα ζαχαροπλαστικής
• sodium carbonate    (χημ.) ανθρακική σόδα
• sodium chloride    χλωριούχο νάτριο
• sodium hydroxide    (χημ.) καυστική σόδα
• sodium lamp    φανάρι του δρόμου
• sodium nitrate    νιτρικό νάτριο
• sodium-vapour lamp    φανάρι του δρόμου

Italiano (Italian)
sodio

idioms:

• sodium bicarbonate    bicarbonato di sodio
• sodium carbonate    carbonato di sodio
• sodium chloride    cloruro di sodio
• sodium hydroxide    soda caustica
• sodium lamp    lampada al sodio
• sodium nitrate    nitrato di sodio
• sodium-vapour lamp    lampada ai vapori di sodio

Português (Portuguese)
n. - sódio (m)

idioms:

• sodium bicarbonate    bicarbonato de sódio (m)
• sodium carbonate    carbonato de sódio (m)
• sodium chloride    cloreto de sódio (m)
• sodium hydroxide    hidróxido de sódio (m)
• sodium lamp    lâmpada de sódio (f)
• sodium nitrate    nitrato de sódio (m)
• sodium-vapour lamp    lâmpada de vapor de sódio (f)

Русский (Russian)
натрий

idioms:

• sodium bicarbonate    двууглекислый натрий
• sodium carbonate    углекислый натрий
• sodium chloride    хлористый натрий, поваренная соль
• sodium hydroxide    едкий натр
• sodium lamp    натриевая лампа
• sodium nitrate    нитрат натрия
• sodium-vapour lamp    натриевая лампа

Español (Spanish)
n. - sodio

idioms:

• sodium bicarbonate    bicarbonato sódico
• sodium carbonate    carbonato sódico
• sodium chloride    cloruro de sodio, cloruro sódico
• sodium hydroxide    hidróxido de sodio
• sodium lamp    lámpara de vapor de sodio
• sodium nitrate    nitrato de sodio
• sodium-vapour lamp    lámpara de vapor de sodio

Svenska (Swedish)
n. - natrium

中文（简体）(Chinese (Simplified))
钠

idioms:

• sodium bicarbonate    碳酸氢钠, 小苏打
• sodium carbonate    碳酸钠
• sodium chloride    食盐, 氯化钠
• sodium hydroxide    氢氧化钠, 烧碱
• sodium lamp    钠灯
• sodium nitrate    硝酸钠
• sodium-vapour lamp    钠蒸气灯

中文（繁體）(Chinese (Traditional))
n. - 鈉

idioms:

• sodium bicarbonate    碳酸氫鈉, 小蘇打
• sodium carbonate    碳酸鈉
• sodium chloride    食鹽, 氯化鈉
• sodium hydroxide    氫氧化鈉, 燒鹼
• sodium lamp    鈉燈
• sodium nitrate    硝酸鈉
• sodium-vapour lamp    鈉蒸氣燈

한국어 (Korean)
n. - 나트륨(금속 원소)

日本語 (Japanese)
n. - ナトリウム

idioms:

• sodium bicarbonate    重炭酸ナトリウム
• sodium carbonate    炭酸ソーダ, 炭酸ナトリウム, 結晶ソーダ
• sodium chloride    塩化ナトリウム
• sodium hydroxide    水酸化ナトリウム, 苛性ソーダ
• sodium lamp    ナトリウムランプ, ナトリウム灯
• sodium nitrate    硝酸ナトリウム

العربيه (Arabic)
‏(الاسم) فلز ألصوديم‏

עברית (Hebrew)
n. - ‮נתרן (יסוד מתכתי, AN, מס' אטומי 11)‬

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