Alkalide

An alkalide is a chemical compound in which alkali metal atoms are anions (negative ions) with a charge or oxidation state of –1. Until the first discovery of alkalides in the 1970s,[1][2][3] alkali metals were only known to appear in salts only as cations (positive ions) with a charge or oxidation state of +1.[4] These types of compounds are of theoretical interest due to their unusual stoichiometry and low ionization potentials. Alkalide compounds are chemically related to the electrides, salts in which trapped electrons are effectively the anions.[5]

"Normal" alkali metal compounds

Alkali metals form many well-known stable salts. Sodium chloride (common table salt), Na+Cl, illustrates the usual role of an alkali metal such as sodium. In the empirical formula for this ionic compound, the positively charged sodium ion balanced by a negatively charged chloride ion. The traditional explanation for stable Na+ is that the loss of one electron from elemental sodium to produce a cation with charge of +1 produces a stable closed-shell electron configuration.

Nomenclature and known cases

There are known alkalides for some of the alkali metals:

  • Sodide or natride, Na
  • Potasside or kalide, K
  • Rubidide, Rb
  • Caeside, Cs

Alkalides of the other alkali metals have not yet been discovered:

  • "Lithides", Li
  • "Francides", Fr

Examples

Normally, alkalides are thermally labile due to the high reactivity of the alkalide anion, which is theoretically able to break most covalent bonds including the C–O bonds in a typical cryptand. The introduction of a special cryptand ligand containing amines instead of ether linkages has allowed the isolation of kalides and natrides that are stable at room temperature.[6]

Several alkalides have been synthesized:

  • (Me3N-H)+Na, known as "inverse sodium hydride", has been observed.[7]
  • Sodium-crypt natride, [Na(cryptand[2.2.2])]+Na, has been observed. This salt contains both Na+ and Na. The cryptand isolates and stabilizes the Na+, preventing it from being reduced by the Na.
  • Barium azacryptand-sodide, Ba2+(H5Azacryptand[2.2.2])Na⋅2MeNH2, has been synthesized.[5]
  • Dimers of cationic and anionic sodium have been observed.[5]

References

  1. ^ J. L. Dye; J. M. Ceraso; Mei Lok Tak; B. L. Barnett; F. J. Tehan (1974). "Crystalline salt of the sodium anion (Na)". J. Am. Chem. Soc. 96 (2): 608–609. doi:10.1021/ja00809a060.
  2. ^ F. J. Tehan; B. L. Barnett; J. L. Dye (1974). "Alkali anions. Preparation and crystal structure of a compound which contains the cryptated sodium cation and the sodium anion". J. Am. Chem. Soc. 96 (23): 7203–7208. doi:10.1021/ja00830a005.
  3. ^ J. L. Dye (1979). "Compounds of Alkali Metal Anions". Angew. Chem. Int. Ed. Engl. 18 (8): 587–598. doi:10.1002/anie.197905871.
  4. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  5. ^ a b c M. Y. Redko; R. H. Huang; J. E. Jackson; J. F. Harrison; J. L. Dye (2003). "Barium azacryptand sodide, the first alkalide with an alkaline Earth cation, also contains a novel dimer, (Na2)2−". J. Am. Chem. Soc. 125 (8): 2259–2263. doi:10.1021/ja027241m. PMID 12590555.
  6. ^ J. Kim; A. S. Ichimura; R. H. Huang; M. Redko; R. C. Phillips; J. E. Jackson; J. L. Dye (1999). "Crystalline Salts of Na and K (Alkalides) that Are Stable at Room Temperature". J. Am. Chem. Soc. 121 (45): 10666–10667. doi:10.1021/ja992667v.
  7. ^ M. Y. Redko; M. Vlassa; J. E. Jackson; A. W. Misiolek; R. H. Huang RH; J. L. Dye (2002). ""Inverse sodium hydride": a crystalline salt that contains H+ and Na". J. Am. Chem. Soc. 124 (21): 5928–5929. doi:10.1021/ja025655.
18-Crown-6

18-Crown-6 is an organic compound with the formula [C2H4O]6 and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 106 M−1). The point group of 18-crown-6 is S6. The dipole moment of 18-crown-6 varies in different solvent and under different temperature. Under 25 °C, the dipole moment of 18-crown-6 is 2.76 ± 0.06 D in cyclohexane and 2.73 ± 0.02 in benzene. The synthesis of the crown ethers led to the awarding of the Nobel Prize in Chemistry to Charles J. Pedersen.

Alkali metal

The alkali metals are a group (column) in the periodic table consisting of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). This group lies in the s-block of the periodic table of elements as all alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour.

The alkali metals are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation by atmospheric moisture and oxygen (and in the case of lithium, nitrogen). Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, excluding hydrogen (H), which is nominally a group 1 element but not normally considered to be an alkali metal as it rarely exhibits behaviour comparable to that of the alkali metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.

All of the discovered alkali metals occur in nature as their compounds: in order of abundance, sodium is the most abundant, followed by potassium, lithium, rubidium, caesium, and finally francium, which is very rare due to its extremely high radioactivity; francium occurs only in the minutest traces in nature as an intermediate step in some obscure side branches of the natural decay chains. Experiments have been conducted to attempt the synthesis of ununennium (Uue), which is likely to be the next member of the group, but they have all met with failure. However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements; even if it does turn out to be an alkali metal, it is predicted to have some differences in physical and chemical properties from its lighter homologues.

Most alkali metals have many different applications. One of the best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks, of which caesium atomic clocks are the most accurate and precise representation of time. A common application of the compounds of sodium is the sodium-vapour lamp, which emits light very efficiently. Table salt, or sodium chloride, has been used since antiquity. Lithium finds use as a psychiatric medication. Sodium and potassium are also essential elements, having major biological roles as electrolytes, and although the other alkali metals are not essential, they also have various effects on the body, both beneficial and harmful.

Aztec cuisine

Aztec cuisine is the cuisine of the former Aztec Empire and the Nahua peoples of the Valley of Mexico prior to European contact in 1519.

The most important staple was corn (maize), a crop that was so important to Aztec society that it played a central part in their mythology. Just like wheat in much of Europe or rice in most of East Asia, it was the food without which a meal was not a meal. It came in varieties that differed in color, texture, size and prestige, and was eaten as corn tortillas, tamales or ātōlli, maize gruel. The other constants of Aztec food were salt and chili peppers and the basic definition of Aztec fasting was to abstain from these two flavors.

The other major foods were beans and New World varieties of the grains amaranth (or pigweed), and chia. The combination of maize and these basic foods would have provided the average Aztec a very well-rounded diet without any significant deficiencies in vitamins or minerals. The cooking of maize grains in alkaline solutions, a process called nixtamalization, significantly raised the nutritional value of the common staple.

Water, maize gruels and pulque (iztāc octli), the fermented juice of the century plant (maguey in Spanish), were the most common drinks, and there were many different fermented alcoholic beverages made from honey, cacti and various fruits. The elite took pride in not drinking pulque, a drink of commoners, and preferred drinks made from cacao, among the most prestigious luxuries available. Favored by rulers, warriors and nobles, they were flavored with chili peppers, honey and a seemingly endless list of spices and herbs.

The Aztec diet included a variety of fish and wild game: various fowl, pocket gophers, green iguanas, axolotls (a type of water salamander), a type of crayfish called an acocil, and a great variety of insects, larvae and insect eggs. They also domesticated turkeys, duck and dogs as food and at times ate meat from larger wild animals such as deer, but none of these were a major part of their diet. They ate various mushrooms and fungi, including the parasitic corn smut, which grows on ears of corn. Squash (also known as Cucurbita) was very popular and came in many different varieties. Squash seeds, fresh, dried or roasted, were especially popular. Tomatoes, though different from the varieties common today, were often mixed with chili in sauces or as filling for tamales.

Eating in Aztec culture could take on a sacred meaning, especially as evidenced in ritual cannibalism. The act of eating another human was deeply connected to the Aztec mythology, in which gods needed to consume the sacrificed flesh and blood of humans to sustain themselves, and the world. One way to look at this is that since human flesh was a food of the gods, it was sacred, and consuming sacred food could sanctify an individual and bring him or her closer to the gods. Further, certain warriors, in their afterlife, were believed to have been turned into butterflies and hummingbirds with the ability to fly back to the realm of the living to feed on nectar. From this, the importance the Aztecs ascribed to the act of eating is clear.

List of A.T.O.M. characters

A.T.O.M. is a French-American action animated series created by Ariane Desrieux and Paul-Patrick Duval. The show takes place in the fictional Landmark City and focuses on five teenagers, the eponymous Alpha Teens on Machines, who are given prototype weapons, gadgets and vehicles in order to battle Alexander Paine, a man who threatens to destroy Landmark City.

Potassium

Potassium is a chemical element with symbol K (from Neo-Latin kalium) and atomic number 19. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight), and is part of many minerals.

Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table. They have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, and was proven in 1807 using electrolysis. Naturally occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, and it is the most common radioisotope in the human body.

Potassium ions are vital for the functioning of all living cells. The transfer of potassium ions through nerve cell membranes is necessary for normal nerve transmission; potassium deficiency and excess can each result in numerous signs and symptoms, including an abnormal heart rhythm and various electrocardiographic abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys.

Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production.

Sodium

Sodium is a chemical element with symbol Na (from Latin natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table, because it has a single electron in its outer shell that it readily donates, creating a positively charged ion—the Na+ cation. Its only stable isotope is 23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and rock salt (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.

Sodium was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Among many other useful sodium compounds, sodium hydroxide (lye) is used in soap manufacture, and sodium chloride (edible salt) is a de-icing agent and a nutrient for animals including humans.

Sodium is an essential element for all animals and some plants. Sodium ions are the major cation in the extracellular fluid (ECF) and as such are the major contributor to the ECF osmotic pressure and ECF compartment volume. Loss of water from the ECF compartment increases the sodium concentration, a condition called hypernatremia. Isotonic loss of water and sodium from the ECF compartment decreases the size of that compartment in a condition called ECF hypovolemia.

By means of the sodium-potassium pump, living human cells pump three sodium ions out of the cell in exchange for two potassium ions pumped in; comparing ion concentrations across the cell membrane, inside to outside, potassium measures about 40:1, and sodium, about 1:10. In nerve cells, the electrical charge across the cell membrane enables transmission of the nerve impulse—an action potential—when the charge is dissipated; sodium plays a key role in that activity.

Sodium hydride

Sodium hydride is the chemical compound with the empirical formula NaH. This alkali metal hydride is primarily used as a strong, yet combustible base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as borane, methane, ammonia and water. It is an ionic material that is insoluble in organic solvents (although soluble in molten Na), consistent with the fact that H− remains an unknown anion in solution. Because of the insolubility of NaH, all reactions involving NaH occur at the surface of the solid.

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