Tamil Nadu
Tamil Nadu is one of the 29 states of India. Its capital and largest city is Chennai. Tamil Nadu lies in the southernmost part of the Indian subcontinent and is bordered by the union territory of Puducherry and the South Indian states of Kerala and Andhra Pradesh, it is bounded by the Eastern Ghats on the north, by the Nilgiri Mountains, the Meghamalai Hills, Kerala on the west, by the Bay of Bengal in the east, by the Gulf of Mannar and the Palk Strait on the southeast, by the Indian Ocean on the south. The state shares a maritime border with the nation of Sri Lanka. Tamil Nadu is the sixth largest by population, it has a high HDI ranking among Indian states as of 2017. The economy of Tamil Nadu is the second-largest state economy in India with ₹17.25 lakh crore in gross domestic product after Maharashtra and a per capita GDP of ₹167,000. It was ranked as one of the top seven developed states in India based on a "Multidimensional Development Index" in a 2013 report published by the Reserve Bank of India.
Its official language is Tamil, one of the longest-surviving classical languages in the world. The region was ruled by several empires, including the three great empires – Chola and Pandyan empires, which shape the region's cuisine and architecture; the British Colonial rule during the modern period led to the emergence of Chennai known as Madras, as a world-class city. Modern-day Tamil Nadu was formed in 1956 after the reorganization of states on linguistic lines; the state is home to a number of historic buildings, multi-religious pilgrimage sites, hill stations and three World Heritage sites. Archaeological evidence points to this area being one of the longest continuous habitations in the Indian peninsula. In Attirampakkam, archaeologists from the Sharma Centre for Heritage Education excavated ancient stone tools which suggests that a humanlike population existed in the Tamil Nadu region somewhere around 300,000 years before homo sapiens arrived from Africa. In Adichanallur, 24 km from Tirunelveli, archaeologists from the Archaeological Survey of India unearthed 169 clay urns containing human skulls, bones, grains of rice, charred rice and celts of the Neolithic period, 3,800 years ago.
The ASI archaeologists have proposed that the script used at that site is "very rudimentary" Tamil Brahmi. Adichanallur has been announced as an archaeological site for further excavation and studies. About 60 per cent of the total epigraphical inscriptions found by the ASI in India are from Tamil Nadu, most of these are in the Tamil language. A Neolithic stone celt with the Indus script on it was discovered at Sembian-Kandiyur near Mayiladuthurai in Tamil Nadu. According to epigraphist Iravatham Mahadevan, this was the first datable artefact bearing the Indus script to be found in Tamil Nadu. According to Mahadevan, the find was evidence of the use of the Harappan language, therefore that the "Neolithic people of the Tamil country spoke a Harappan language"; the date of the celt was estimated at between 1500 BCE and 2000 BCE. Though this finding remains contested,like the claim of historian Michel Danino who rubbishes the theory of the latter’s southward migration in a paper he presented at the International Symposium on Indus Civilisation and Tamil Language in 2007.
He wrote: ‘There is no archaeological evidence of a southward migration through the Deccan after the end of the urban phase of the Indus- Sarasvati civilization… The only actual evidence of movements at that period is of Late Harappans migrating towards the Ganges plains and towards Gujarat... Migration apart, there is a complete absence of Harappan artefacts and features south of the Vindhyas: no Harappan designs on pottery, no Harappan seals and ornaments, no trace of Harappan urbanism… Cultural continuity from Harappan to historical times has been documented in North India, but not in the South… This means, in effect, that the south-bound Late Harappans would have reverted from an advanced urban bronze-age culture to a Neolithic one! Their migration to South would thus constitute a double “archaeological miracle”: apart from being undetectable on the ground, it implies that the migrants experienced a total break with all their traditions; such a phenomenon is unheard of.’ The early history of the people and rulers of Tamil Nadu is a topic in Tamil literary sources known as Sangam literature.
Numismatic and literary sources corroborate that the Sangam period lasted for about eight centuries, from 500 BC to AD 300. The recent excavations in Alagankulam archaeological site suggests that Alagankulam is one of the important trade centre or port city in Sangam Era; the Bhakti movement originated in Tamil speaking region of South India and spread northwards through India. The Bhakti Movement was a rapid growth of bhakti beginning in this region with the Saiva Nayanars and the Vaisnava Alvars who spread bhakti poetry and devotion; the Alwars and Nayanmars were instrumental in propagating the Bhakti tradition. During the 4th to 8th centuries, Tamil Nadu saw the rise of the Pallava dynasty under Mahendravarman I and his son Mamalla Narasimhavarman I; the Pallavas ruled parts of South India with Kanchipuram as their capital. Tamil architecture reached its peak during Pallava rule. Narasimhavarman II built the Shore Temple, a UNESCO World Heritage Site. Much the Pallavas were replaced by the Chola dynasty as the dominant kingdom in the 9th century and they in turn were replaced by the Pandyan Dynasty in the 13th century.
The Pandyan capital Madurai was in the deep s
Borate
Borates are the name for a large number of boron-containing oxyanions. The term "borates" may refer to tetrahedral boron anions, or more loosely to chemical compounds which contain borate anions of either description. Larger borates are composed of trigonal planar BO3 or tetrahedral BO4 structural units, joined together via shared oxygen atoms and may be cyclic or linear in structure. Boron most occurs in nature as borates, such as borate minerals and borosilicates; the simplest borate anion, the orthoborate ion, 3-, is known in the solid state, for example in Ca32. In this it adopts a near trigonal planar structure, it is a structural analogue of the carbonate anion 2 -. Simple bonding theories point to the trigonal planar structure. In terms of valence bond theory the bonds are formed by using sp2 hybrid orbitals on boron; some compounds termed orthoborates do not contain the trigonal planar ion, for example gadolinium orthoborate, GdBO3 contains the polyborate 9- ion, whereas the high temperature form contains planar 3-.
All borates can be considered derivatives of boric acid, B3. Boric acid is a weak proton donor in the sense of Brønsted acid, but is a Lewis acid, i.e. it can accept an electron pair. In water, it behaves as a Lewis acid accepting the electron pair of a hydroxyl ion produced by the water autoprotolysis. So, B3 is acidic because of its reaction with OH– from water, forming the tetrahydroxyborate complex − and releasing the corresponding proton left by the water autoprotolysis: B3 + 2H2O ⇌ − + + In the presence of cis-diols such as mannitol, glucose and glycerol the pKa is lowered to about 4. At neutral pH boric acid undergoes condensation reactions to form polymeric oxyanions. Well-known polyborate anions include the triborate and pentaborate anions; the condensation reaction for the formation of tetraborate is as follows: 2 B3 + 2 − ⇌ 2- + 5 H2OThe tetraborate anion includes two tetrahedral and two trigonal boron atoms symmetrically assembled in a fused bicyclic structure. The two tetrahedral boron atoms are linked together by a common oxygen atom and each bears a negative net charge brought by the supplementary OH− groups laterally attached to them.
This intricate molecular anion exhibits three rings: two fused distorted hexagonal rings and one distorted octagonal ring. Each ring is made of a succession of alternate oxygen atoms. Boroxole rings are a common structural motif in polyborate ions; the tetraborate anion occurs in the mineral borax, as an octahydrate, Na2·8H2O. The borax chemical formula is commonly written in a more compact notation as Na2B4O7·10H2O. Sodium borate can be obtained in high purity and so can be used to make a standard solution in titrimetric analysis. A number of metal borates are known, they arise by treating boric boron oxides with metal oxides. Examples hereafter include linear chains of 2, 3 or 4 trigonal BO3 structural units, each sharing only one oxygen atom with adjacent unit: diborate 4-, found in Mg2B2O5 triborate 5-, found in CaAlB3O7 tetraborate 6-, found in Li6B4O9Metaborates, such as LiBO2 contain chains of trigonal BO3 structural units, each sharing two oxygen atoms with adjacent units, whereas NaBO2 and KBO2 contain the cyclic 2- ion.
Borosilicate glass known as pyrex, can be viewed as a silicate in which some 4- units are replaced by 5- centers, together with additional cations to compensate for the difference in valence states of Si and B. Because of this substitution leads to imperfections, the material is slow to crystallise and forms a glass with low coefficient of thermal expansion and is resistant to cracking when heated, unlike soda glass. Common borate salts include sodium metaborate, NaBO2, borax. Borax is soluble in water, so mineral deposits only occur in places with low rainfall. Extensive deposits were found in Death Valley and transported out using the famous twenty-mule teams. Deposits were found at Boron, California on the edge of the Mojave Desert; the Atacama Desert in Chile contains mineable borate concentrations. Lithium metaborate or lithium tetraborate, or a mixture of both, can be used in borate fusion sample preparation of various samples for analysis by XRF, AAS, ICP-OES, ICP-AES and ICP-MS. Borate fusion and energy dispersive X-ray fluorescence spectrometry with polarized excitation have been used in the analysis of contaminated soils.
Disodium octaborate tetrahydrate is used as fungicide. Zinc borate is used as a flame retardant. Borate esters are organic compounds which are conveniently prepared by the stoichiometric condensation reaction of boric acid with alcohols. Borax Nanochannel glass materials Porous glass Vycor glass Tris borate Suanite at webmineral Johachidolite at webmineral Non-CCA Wood Preservatives: Guide to Selected Resources - National Pesticide Information Center
Prehistory
Human prehistory is the period between the use of the first stone tools c. 3.3 million years ago by hominins and the invention of writing systems. The earliest writing systems appeared c. 5,300 years ago, but it took thousands of years for writing to be adopted, it was not used in some human cultures until the 19th century or until the present. The end of prehistory therefore came at different dates in different places, the term is less used in discussing societies where prehistory ended recently. Sumer in Mesopotamia, the Indus valley civilization, ancient Egypt were the first civilizations to develop their own scripts and to keep historical records. Neighboring civilizations were the first to follow. Most other civilizations reached the end of prehistory during the Iron Age; the three-age system of division of prehistory into the Stone Age, followed by the Bronze Age and Iron Age, remains in use for much of Eurasia and North Africa, but is not used in those parts of the world where the working of hard metals arrived abruptly with contact with Eurasian cultures, such as the Americas, Oceania and much of Sub-Saharan Africa.
These areas with some exceptions in Pre-Columbian civilizations in the Americas, did not develop complex writing systems before the arrival of Eurasians, their prehistory reaches into recent periods. The period when a culture is written about by others, but has not developed its own writing is known as the protohistory of the culture. By definition, there are no written records from human prehistory, so dating of prehistoric materials is crucial. Clear techniques for dating were not well-developed until the 19th century; this article is concerned with human prehistory, the time since behaviorally and anatomically modern humans first appeared until the beginning of recorded history. Earlier periods are called "prehistoric". Beginning The term "prehistory" can refer to the vast span of time since the beginning of the Universe or the Earth, but more it refers to the period since life appeared on Earth, or more to the time since human-like beings appeared. End The date marking the end of prehistory is defined as the advent of the contemporary written historical record.
The date varies from region to region depending on the date when relevant records become a useful academic resource. For example, in Egypt it is accepted that prehistory ended around 3200 BCE, whereas in New Guinea the end of the prehistoric era is set much more at around 1900 common era. In Europe the well-documented classical cultures of Ancient Greece and Ancient Rome had neighbouring cultures, including the Celts and to a lesser extent the Etruscans, with little or no writing, historians must decide how much weight to give to the highly prejudiced accounts of these "prehistoric" cultures in Greek and Roman literature. Time periods In dividing up human prehistory in Eurasia, historians use the three-age system, whereas scholars of pre-human time periods use the well-defined geologic record and its internationally defined stratum base within the geologic time scale; the three-age system is the periodization of human prehistory into three consecutive time periods, named for their respective predominant tool-making technologies: Stone Age Bronze Age Iron Age The notion of "prehistory" began to surface during the Enlightenment in the work of antiquarians who used the word'primitive' to describe societies that existed before written records.
The first use of the word prehistory in English, occurred in the Foreign Quarterly Review in 1836. The use of the geologic time scale for pre-human time periods, of the three-age system for human prehistory, is a system that emerged during the late nineteenth century in the work of British and Scandinavian archeologists and anthropologists; the main source for prehistory is archaeology, but some scholars are beginning to make more use of evidence from the natural and social sciences. This view has been articulated by advocates of deep history; the primary researchers into human prehistory are archaeologists and physical anthropologists who use excavation and geographic surveys, other scientific analysis to reveal and interpret the nature and behavior of pre-literate and non-literate peoples. Human population geneticists and historical linguists are providing valuable insight for these questions. Cultural anthropologists help provide context for societal interactions, by which objects of human origin pass among people, allowing an analysis of any article that arises in a human prehistoric context.
Therefore, data about prehistory is provided by a wide variety of natural and social sciences, such as paleontology, archaeology, geology, comparative linguistics, molecular genetics and many others. Human prehistory differs from history not only in terms of its chronology but in the way it deals with the activities of archaeological cultures rather than named nations or individuals. Restricted to material processes and artifacts rather than written records, prehistory is anonymous; because of this, reference terms that prehistorians use, such as Neanderthal or Iron Age are modern labels with definitions sometimes subject to debate. The concept of a "Stone Age" is found useful in the archaeology of most of the world, though in the archaeology of the Americas it is called by different names and begins with a Lithic sta
Salt evaporation pond
A salt evaporation pond is a shallow artificial salt pan designed to extract salts from sea water or other brines. Natural salt pans are geological formations that are created by water evaporating and leaving behind salts; some salt evaporation ponds are only modified from their natural version, such as the ponds on Great Inagua in the Bahamas, or the ponds in Jasiira, a few kilometres south of Mogadishu, where seawater is trapped and left to evaporate in the sun. The seawater or brine is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be subsequently harvested; the ponds provide a productive resting and feeding ground for many species of waterbirds, which may include endangered species. The ponds are separated by levees. Salt evaporation ponds called salterns, salt works or salt pans, are shallow artificial ponds designed to extract salts from sea water or other brines; the seawater or brine is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be subsequently harvested.
Due to variable algal concentrations, vivid colors are created in the evaporation ponds. The color indicates the salinity of the ponds. Microorganisms change their hues as the salinity of the pond increases. In low- to mid-salinity ponds, green algae such as Dunaliella salina are predominant, although these algae can take on an orange hue. In middle- to high-salinity ponds, a group of halophilic Archaea, shift the colour to pink and orange. Other bacteria such as Stichococcus contribute tints. Notable salt ponds include: The Salterns of Guérande, in Loire-Atlantique, the last artisanal salt production in France; the salt produced in the salterns are a Protected geographical indication in Europe The Salineras de Maras, Peru, in the Cusco Region The El Caracol solar evaporator, on the outskirts of Mexico City, Mexico The Sečovlje and Strunjan salt ponds on the northern edge of the Adriatic Sea in Slovenia, The San Francisco Bay salt ponds in the United States, operated by Cargill, including Charleston Slough The Dead Sea salt ponds in the West Bank and Jordan The salt ponds in Salina, Malta.
The name of the village is the Maltese word for salt pan The Port Hedland, Lake McLeod, Useless Loop and Onslow salt ponds in Western Australia Yellow Walls, Ireland. Lake Grassmere in New ZealandUntil World War II, salt was extracted from sea water in a unique way in Egypt near Alexandria. Posts were covered with several feet of sea water. In time the sea water evaporated, leaving the salt behind on the post, where it was easier to harvest. Salt pans are shallow open metal, pans used to evaporate brine, they are found close to the source of the salt. For example, pans used in the solar evaporation of salt from sea water are found on the coast, while those used to extract salt from solution-mined brine will be found near to the brine shaft. In this case, extra heat is provided by lighting fires underneath. Solar desalination Seawater Greenhouse Evaporite NASA page on salt ponds Information on the San Francisco Bay salt ponds Interactive satellite view "Salt, Grown On Sticks Harvested From Sea" Popular Science, March 1933
Turks and Caicos Islands
The Turks and Caicos Islands are a British Overseas Territory consisting of the larger Caicos Islands and smaller Turks Islands, two groups of tropical islands in the Lucayan Archipelago of the Atlantic Ocean and northern West Indies. They are known for tourism and as an offshore financial centre; the resident population is 31,458 as of 2012 of whom 23,769 live on Providenciales in the Caicos Islands. It is the third largest of the British overseas territories by population; the Turks and Caicos Islands lie southeast of Mayaguana in the Bahamas island chain, northeast of Cuba, of the island of Hispaniola and the other Antilles archipelago islands. Cockburn Town, the capital since 1766, is situated on Grand Turk Island about 1,042 kilometres east-southeast of Miami, United States; the islands have a total land area of 430 square kilometres. The first recorded European sighting of the islands now known as the Turks and Caicos occurred in 1512. In the subsequent centuries, the islands were claimed by several European powers with the British Empire gaining control.
For many years the islands were governed indirectly through Bermuda, the Bahamas, Jamaica. When the Bahamas gained independence in 1973, the islands received their own governor, have remained a separate autonomous British Overseas Territory since; the Turks and Caicos Islands are named after the Turk's cap cactus, the Lucayan term caya hico, meaning'string of islands'. The first inhabitants of the islands were Arawakan-speaking Taíno people, who crossed over from Hispaniola some time from AD 500 to 800. Together with Taino who migrated from Cuba to the southern Bahamas around the same time, these people developed as the Lucayan. Around 1200, the Turks and Caicos Islands were resettled by Classical Taínos from Hispaniola. Soon after the Spanish arrived in the islands in 1512, they began capturing the Taíno of the Turks and Caicos Islands and the Lucayan as slaves to replace the depleted native population of Hispaniola; the southern Bahama Islands and the Turks and Caicos Islands were depopulated by about 1513, remained so until the 17th century.
The first European documented to sight the islands was Spanish conquistador Juan Ponce de León, who did so in 1512. During the 16th, 17th, 18th centuries, the islands passed from Spanish to French, to British control, but none of the three powers established any settlements. Bermudian salt collectors settled the Turks Islands around 1680. For several decades around the turn of the 18th century, the islands became popular pirate hideouts. From 1765–1783, the islands were under French occupation, again after the French captured the archipelago in 1783. After the American War of Independence, many Loyalists fled to British Caribbean colonies, they developed cotton as an important cash crop, but it was superseded by the development of the salt industry. In 1799, both the Turks and the Caicos island groups were annexed by Britain as part of the Bahamas; the processing of sea salt was developed as a important export product from the West Indies, with the labour done by African slaves. Salt continued to be a major export product into the nineteenth century.
In 1807, Britain, in 1833, abolished slavery in its colonies. British ships sometimes intercepted slave traders in the Caribbean, some ships were wrecked off the coast of these islands. In 1837, the Esperanza, a Portuguese slaver, was wrecked off one of the larger islands. While the crew and 220 captive Africans survived the shipwreck, 18 Africans died before the survivors were taken to Nassau. Africans from this ship may have been among the 189 liberated Africans whom the British colonists settled in the Turks and Caicos from 1833 to 1840. In 1841, the Trouvadore, an illegal Spanish slave ship, was wrecked off the coast of East Caicos. All the 20-man crew and 192 captive Africans survived the sinking. Officials freed the Africans and arranged for 168 persons to be apprenticed to island proprietors on Grand Turk Island for one year, they increased the small population of the colony by seven percent. Numerous descendants have come from those free Africans; the remaining 24 were resettled in Nassau.
The Spanish crew were taken there, to be turned over to the custody of the Cuban consul and taken to Cuba for prosecution. An 1878 letter documents the "Trouvadore Africans" and their descendants as constituting an essential part of the "labouring population" on the islands. In 2004, marine archaeologists affiliated with the Turks and Caicos National Museum discovered a wreck, called the "Black Rock Ship", that subsequent research has suggested may be that of the Trouvadore. In November 2008, a cooperative marine archaeology expedition, funded by the United States NOAA, confirmed that the wreck has artefacts whose style and date of manufacture link them to the Trouvadore. In 1848, Britain designated the Caicos as a separate colony under a council president. In 1873, the islands were made part of the Jamaica colony. In 1917, Canadian Prime Minister Robert Borden suggested that the Turks and Caicos join Canada, but this suggestion was rejected by British Prime Minister David Lloyd George; the islands remained a dependency of Jamaica.
On 4 July 1959, the islands were again designated as a separate colony, the last commissioner being restyled administrator. The governor of Jamaica continued as the governor of the islands; when Jamaica was granted independence from Britain in August 1962, the Turks and Caicos Islands became a Crown colony. B
The Bahamas
The Bahamas, known as the Commonwealth of The Bahamas, is a country within the Lucayan Archipelago. The archipelagic state consists of more than 700 islands and islets in the Atlantic Ocean, is located north of Cuba and Hispaniola, northwest of the Turks and Caicos Islands, southeast of the U. S. state of Florida, east of the Florida Keys. The capital is Nassau on the island of New Providence; the designation of "the Bahamas" can refer either to the country or to the larger island chain that it shares with the Turks and Caicos Islands. The Royal Bahamas Defence Force describes the Bahamas territory as encompassing 470,000 km2 of ocean space; the Bahamas is the site of Columbus's first landfall in the New World in 1492. At that time, the islands were inhabited by the Lucayans, a branch of the Arawakan-speaking Taíno people. Although the Spanish never colonised the Bahamas, they shipped the native Lucayans to slavery in Hispaniola; the islands were deserted from 1513 until 1648, when English colonists from Bermuda settled on the island of Eleuthera.
The Bahamas became a British crown colony in 1718. After the American Revolutionary War, the Crown resettled thousands of American Loyalists in the Bahamas. Africans constituted the majority of the population from this period; the slave trade was abolished by the British in 1807. Subsequently, the Bahamas became a haven for freed African slaves. Today, Afro-Bahamians make up nearly 90% of the population; the Bahamas became an independent Commonwealth realm in 1973 with Elizabeth II as its queen. In terms of gross domestic product per capita, the Bahamas is one of the richest countries in the Americas, with an economy based on tourism and finance; the name Bahamas is most derived from either the Taíno ba ha ma, a term for the region used by the indigenous Native Americans, or from the Spanish baja mar reflecting the shallow waters of the area. Alternatively, it may originate from a local name of unclear meaning; the word The constitutes an integral part of the short form of the name and is, capitalised.
So in contrast to "the Congo" and "the United Kingdom", it is proper to write "The Bahamas." The name The Bahamas is thus comparable with certain non-English names that use the definite article, such as Las Vegas or Los Angeles. The Constitution of the Commonwealth of The Bahamas, the country's fundamental law, capitalizes the "T" in "The Bahamas." Taino people moved into the uninhabited southern Bahamas from Hispaniola and Cuba around the 11th century, having migrated there from South America. They came to be known as the Lucayan people. An estimated 30,000 Lucayans inhabited the Bahamas at the time of Christopher Columbus's arrival in 1492. Columbus's first landfall in the New World was on an island; some researchers believe this site to be present-day San Salvador Island, situated in the southeastern Bahamas. An alternative theory holds that Columbus landed to the southeast on Samana Cay, according to calculations made in 1986 by National Geographic writer and editor Joseph Judge, based on Columbus's log.
Evidence in support of this remains inconclusive. On the landfall island, Columbus exchanged goods with them; the Spanish forced much of the Lucayan population to Hispaniola for use as forced labour. The slaves suffered from harsh conditions and most died from contracting diseases to which they had no immunity; the population of the Bahamas was diminished. In 1648, the Eleutherian Adventurers, led by William Sayle, migrated from Bermuda; these English Puritans established the first permanent European settlement on an island which they named Eleuthera—the name derives from the Greek word for freedom. They settled New Providence, naming it Sayle's Island after one of their leaders. To survive, the settlers salvaged goods from wrecks. In 1670, King Charles II granted the islands to the Lords Proprietors of the Carolinas in North America, they rented the islands from the king with rights of trading, appointing governors, administering the country. In 1684 Spanish corsair Juan de Alcon raided Charles Town.
In 1703, a joint Franco-Spanish expedition occupied the Bahamian capital during the War of the Spanish Succession. During proprietary rule, the Bahamas became a haven for pirates, including Blackbeard. To put an end to the'Pirates' republic' and restore orderly government, Great Britain made the Bahamas a crown colony in 1718 under the royal governorship of Woodes Rogers. After a difficult struggle, he succeeded in suppressing piracy. In 1720, Rogers led local militia to drive off a Spanish attack. During the US War of Independence in the late 18th century, the islands became a target for US naval forces under the command of Commodore Esek Hopkins. US Marines occupied the capital of Nassau for 2 weeks. In 1782, following the British defeat at Yorktown, a Spanish fleet appeared off the coast of Nassau; the city surrendered without a fight. Spain returned possession of the Bahamas to Great Britain the following year, u
Potassium
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from 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, 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 in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, burning with a lilac-colored flame, it is found dissolved in sea water, is part of many minerals. Potassium is chemically 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, was proven in 1807 using electrolysis.
Occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, 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 across nerve cell membranes is necessary for normal nerve transmission. 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 depletes the soil of potassium, this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production; the English name for the element potassium comes from the word "potash", which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water and evaporating the solution.
When Humphry Davy first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash. The symbol "K" stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, realized that "potash" was not a product of plant growth but contained a new element, which he proposed to call kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K"; the English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K.
Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, can be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray on exposure to air. In a flame test and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon; because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that potassium is oxidized by atmospheric oxygen. In contrast, the second ionization energy is high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not form compounds with the oxidation state of higher. Potassium is an active metal that reacts violently with oxygen in water and air.
With oxygen it forms potassium peroxide, with water potassium forms potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium; this reaction requires only traces of water. Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral kerosene, it dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal s
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