Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption . Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, tuffaceous sandstone ). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone .
153-558: Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the moai statues on Easter Island . Tuff can be classified as either igneous or sedimentary rock . It is usually studied in the context of igneous petrology , although it is sometimes described using sedimentological terms. Tuff
306-530: A bright red line for rubidium (from the Latin word rubidus , meaning dark red or bright red), and a sky-blue line for caesium (derived from the Latin word caesius , meaning sky-blue). Around 1865 John Newlands produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to
459-509: A certain volume and the mass of one of the atoms, since density is defined as mass per unit volume. The first factor depends on the volume of the atom and thus the atomic radius, which increases going down the group; thus, the volume of an alkali metal atom increases going down the group. The mass of an alkali metal atom also increases going down the group. Thus, the trend for the densities of the alkali metals depends on their atomic weights and atomic radii; if figures for these two factors are known,
612-466: A drop in population. He further hypothesizes that there were about 7,000 individuals pre-war, a number which fell to the 2,000 whom missionaries met when they showed up in the 19th century and conducted the first census of the island. In recent years, this decline has been increasingly implicated not upon environmental destruction caused by the Rapa Nui people but instead upon the arrival of Europeans to
765-569: A giant palm, the Rapa Nui Palm , that showed signs of being the largest palm species in the world, eclipsing the size of the Chilean Wine Palm if it were not extinct. There are also signs of Easter Island's once possessing a far more diverse collection of fauna. The skeletal remains of 25 different species of nesting bird have been located on the island, but have since been reduced to 16. This trend of extinction and extirpation
918-478: A large enough target to increase the sensitivity of the experiment to the required level; einsteinium has not been found in nature and has only been produced in laboratories, and in quantities smaller than those needed for effective synthesis of superheavy elements. However, given that ununennium is only the first period 8 element on the extended periodic table , it may well be discovered in the near future through other reactions, and indeed an attempt to synthesise it
1071-478: A larger explosion than potassium if the same number of moles of each metal is used. The alkali metals have the lowest first ionisation energies in their respective periods of the periodic table because of their low effective nuclear charge and the ability to attain a noble gas configuration by losing just one electron . Not only do the alkali metals react with water, but also with proton donors like alcohols and phenols , gaseous ammonia , and alkynes ,
1224-422: A limiting yield of 300 nb . It is highly unlikely that this reaction will be able to create any atoms of ununennium in the near future, given the extremely difficult task of making sufficient amounts of einsteinium-254, which is favoured for production of ultraheavy elements because of its large mass, relatively long half-life of 270 days, and availability in significant amounts of several micrograms, to make
1377-574: A metamorphosed tuff bed in the Pilar Formation provided some of the first evidence for the Picuris orogeny . The word tuff is derived from the Italian tufo . Rapa Nui people The Rapa Nui (Rapa Nui: [ˈɾapa ˈnu.i] , Spanish: [ˈrapa ˈnu.i] ) are the indigenous Polynesian peoples of Easter Island . The easternmost Polynesian culture, the descendants of
1530-422: A more covalent character. For example, lithium iodide (LiI) will dissolve in organic solvents , a property of most covalent compounds. Lithium fluoride (LiF) is the only alkali halide that is not soluble in water, and lithium hydroxide (LiOH) is the only alkali metal hydroxide that is not deliquescent . The melting point of a substance is the point where it changes state from solid to liquid while
1683-421: A net charge of +1, as some of the nuclear charge (which is equal to the atomic number ) is cancelled by the inner electrons; the number of inner electrons of an alkali metal is always one less than the nuclear charge. Therefore, the only factor which affects the atomic radius of the alkali metals is the number of electron shells. Since this number increases down the group, the atomic radius must also increase down
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#17327810877451836-759: A number of substances not always of identical character. In the historical architecture of Naples, Neapolitan yellow tuff is the most used building material. Piperno ignimbrite tuff was also used widely in Naples and Campania. In the Eifel region of Germany, a trachytic, pumiceous tuff called trass has been extensively worked as a hydraulic mortar . Tuff of the Eifel region of Germany has been widely used for construction of railroad stations and other buildings in Frankfurt, Hamburg, and other large cities. Construction using
1989-762: A result of ancient seas evaporating, which still occurs now in places such as Utah 's Great Salt Lake and the Dead Sea . Despite their near-equal abundance in Earth's crust, sodium is far more common than potassium in the ocean, both because potassium's larger size makes its salts less soluble, and because potassium is bound by silicates in soil and what potassium leaches is absorbed far more readily by plant life than sodium. Despite its chemical similarity, lithium typically does not occur together with sodium or potassium due to its smaller size. Due to its relatively low reactivity, it can be found in seawater in large amounts; it
2142-471: A solid mineral, as opposed to potassium, which had been discovered in plant ashes, and sodium, which was known partly for its high abundance in animal blood. He named the metal inside the material lithium . Lithium, sodium, and potassium were part of the discovery of periodicity , as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner in 1850 as having similar properties. Rubidium and caesium were
2295-492: A strongly basic alkali metal hydroxide and releasing hydrogen gas. This reaction becomes more vigorous going down the group: lithium reacts steadily with effervescence , but sodium and potassium can ignite, and rubidium and caesium sink in water and generate hydrogen gas so rapidly that shock waves form in the water that may shatter glass containers. When an alkali metal is dropped into water, it produces an explosion, of which there are two separate stages. The metal reacts with
2448-473: A symbol of their hierarchy. Both men and women were tattooed to represent their social class. Tattoos, as well as other forms of art in Rapa Nui, blends anthropomorphic and zoomorphic imagery. Nowadays, young people are bringing back Rapa Nui tattoos as an important part of their culture and local artists base their creations on traditional motifs. The tattooing process was performed with bone needles and combs called Uhi made out of bird or fish bones. The ink
2601-407: A system of glyphs discovered in the 1800s, is believed to represent an older version of the Rapa Nui language. However, the decipherment of rongorongo is an ongoing process and it is not yet clear whether Rongorongo is a form of writing or some other form of cultural expression. The main stories of Rapa Nui mythology are that of Hotu Matu'a , believed to be the first settler of Easter Island, and
2754-447: A very smooth trend is their reduction potentials : lithium's value is anomalous, being more negative than the others. This is because the Li ion has a very high hydration energy in the gas phase: though the lithium ion disrupts the structure of water significantly, causing a higher change in entropy, this high hydration energy is enough to make the reduction potentials indicate it as being
2907-401: A water molecule and the metal ion is a dative covalent bond , with the oxygen atom donating both electrons to the bond. Each coordinated water molecule may be attached by hydrogen bonds to other water molecules. The latter are said to reside in the second coordination sphere. However, for the alkali metal cations, the second coordination sphere is not well-defined as the +1 charge on the cation
3060-548: A −1 oxidation state, which is very unusual as before the discovery of the alkalides, the alkali metals were not expected to be able to form anions and were thought to be able to appear in salts only as cations. The alkalide anions have filled s-subshells , which gives them enough stability to exist. All the stable alkali metals except lithium are known to be able to form alkalides, and the alkalides have much theoretical interest due to their unusual stoichiometry and low ionisation potentials . Alkalides are chemically similar to
3213-456: Is a common occurrence when humans populate a new area, because of tendencies to overhunt and overexploit resources. Deforestation would have caused a decrease in crop yields due to soil erosion, loss of wood as a resource to construct fishing boats, among other things, and would have necessitated a halt to the construction of the moai erected around the island. Diamond hypothesizes that resource scarcity may have led to brutal civil war, creating
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#17327810877453366-464: Is also built almost entirely from tuff. The Romans also cut tuff into small, rectangular stones that they used to create walls in a pattern known as opus reticulatum . Peperino has been used in Rome and Naples as a building stone, is a trachyte tuff. Pozzolana also is a decomposed tuff, but of basic character, originally obtained near Naples and used as a cement , but this name is now applied to
3519-435: Is also known as the lithium family after its leading element. 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
3672-831: Is an example of a tuff cone, as is the island of Ka'ula . The glassy basaltic ash produced in such eruptions rapidly alters to palagonite as part of the process of lithification. Although conventional mafic volcanism produce little ash, such ash as is formed may accumulate locally as significant deposits. An example is the Pahala ash of Hawaii island, which locally is as thick as 15 meters (49 ft). These deposits also rapidly alter to palagonite, and eventually weather to laterite . Basaltic tuffs are also found in Skye , Mull , Antrim , and other places, where Paleogene volcanic rocks are found; in Scotland, Derbyshire , and Ireland among
3825-426: Is approximately as abundant as zinc and more abundant than copper. It occurs naturally in the minerals leucite , pollucite , carnallite , zinnwaldite , and lepidolite , although none of these contain only rubidium and no other alkali metals. Caesium is more abundant than some commonly known elements, such as antimony , cadmium , tin , and tungsten , but is much less abundant than rubidium. Francium-223 ,
3978-459: Is as a building material. In the ancient world, tuff's relative softness meant that it was commonly used for construction where it was available. Tuff is common in Italy, and the Romans used it for many buildings and bridges. For example, the whole port of the island of Ventotene (still in use), was carved from tuff. The Servian Wall , built to defend the city of Rome in the fourth century BC,
4131-424: Is baked in the umu pae as well.[1] Other favorite dishes are tunu ahi, fish grilled on hot stones, or ceviche. Pascuense cuisine also includes meat dishes, such as pork or mutton ribs.[2] A common hypothesis is held that the apparent decline of Rapa Nui culture and society before European arrival in 1722 was caused by the over-exploitation of the island's environment, most notably through deforestation of almost all
4284-517: Is called a welded lapilli -tuff. Welded tuffs (and welded lapilli-tuffs) can be of fallout origin, or deposited from ash flows, as in the case of ignimbrites . During welding, the glass shards and pumice fragments adhere together (necking at point contacts), deform, and compact together, resulting in a eutaxitic fabric . Welded tuff is commonly rhyolitic in composition, but examples of all compositions are known. A sequence of ash flows may consist of multiple cooling units . These can be distinguished by
4437-422: Is classified as an Eastern Polynesian language and is currently written in the Latin script. Rapa Nui is a minority language, as most Rapa Nui people speak Spanish as their first language. Spanish is the most widely spoken language on Easter Island and the primary language of education and administration. It is believed that Rapa Nui is currently undergoing a shift toward more Spanish sentence structure. Rongorongo ,
4590-418: Is correspondingly divided into coarse tuff (coarse ash tuff) and fine tuff (fine ash tuff or dust tuff). Consolidated tephra composed mostly of coarser particles is called lapillistone (particles 2 mm to 64 mm in diameter) or agglomerate or pyroclastic breccia (particles over 64 mm in diameter) rather than tuff. Volcanic ash can vary greatly in composition, and so tuffs are further classified by
4743-609: Is currently ongoing in Japan. Currently, none of the period 8 elements has been discovered yet, and it is also possible, due to drip instabilities , that only the lower period 8 elements, up to around element 128, are physically possible. No attempts at synthesis have been made for any heavier alkali metals: due to their extremely high atomic number, they would require new, more powerful methods and technology to make. The Oddo–Harkins rule holds that elements with even atomic numbers are more common that those with odd atomic numbers, with
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4896-459: Is estimated that lithium concentration in seawater is approximately 0.14 to 0.25 parts per million (ppm) or 25 micromolar . Its diagonal relationship with magnesium often allows it to replace magnesium in ferromagnesium minerals, where its crustal concentration is about 18 ppm , comparable to that of gallium and niobium . Commercially, the most important lithium mineral is spodumene , which occurs in large deposits worldwide. Rubidium
5049-556: Is in tuff and ignimbrite in the Basin and Range Province in Nevada . In Napa Valley and Sonoma Valley , California , areas made of tuff are routinely excavated for storage of wine barrels. Tuff from Rano Raraku was used by the Rapa Nui people of Easter Island to make the vast majority of their famous moai statues. Tuff is used extensively in Armenia and Armenian architecture . It
5202-502: Is known as tephrochronology and is particularly useful for Quaternary chronostratigraphy. Individual tuff beds can be "fingerprinted" by their chemical composition and phenocryst assemblages. Absolute ages for tuff beds can be determined by K-Ar , Ar-Ar , or carbon-14 dating . Zircon grains found in many tuffs are highly durable and can survive even metamorphism of the host tuff to schist, allowing absolute ages to be assigned to ancient metamorphic rocks. For example, dating of zircons in
5355-427: Is most accurate for alkali halides and becomes less and less accurate as cationic and anionic charge increase, and as the anion becomes larger and more polarisable. For instance, ionic bonding gives way to metallic bonding along the series NaCl, Na 2 O, Na 2 S, Na 3 P, Na 3 As, Na 3 Sb, Na 3 Bi, Na. All the alkali metals react vigorously or explosively with cold water, producing an aqueous solution of
5508-427: Is not a difference in binding energy between even–odd and odd–even comparable to that between even–even and odd–odd, leaving other nuclides of the same mass number ( isobars ) free to beta decay toward the lowest-mass nuclide. An effect of the instability of an odd number of either type of nucleons is that odd-numbered elements, such as the alkali metals, tend to have fewer stable isotopes than even-numbered elements. Of
5661-440: Is not high enough to polarise the water molecules in the primary solvation shell enough for them to form strong hydrogen bonds with those in the second coordination sphere, producing a more stable entity. The solvation number for Li has been experimentally determined to be 4, forming the tetrahedral [Li(H 2 O) 4 ] : while solvation numbers of 3 to 6 have been found for lithium aqua ions, solvation numbers less than 4 may be
5814-429: Is often erroneously called tufa in guidebooks and in television programs but tufa is a form of travertine . The material that is expelled in a volcanic eruption can be classified into three types: Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to
5967-410: Is similarly slightly radioactive, with 27.83% being the long-lived radioisotope rubidium-87. Caesium-137 , with a half-life of 30.17 years, is one of the two principal medium-lived fission products , along with strontium-90 , which are responsible for most of the radioactivity of spent nuclear fuel after several years of cooling, up to several hundred years after use. It constitutes most of
6120-579: Is the dominant type of stone used in construction in Armenia's capital Yerevan , Gyumri , Armenia's second largest city, and Ani , the country's medieval capital, now in Turkey. A small village in Armenia was renamed Tufashen (literally "village of tuff") in 1946. Tuffs are deposited geologically instantaneously and often over a large region. This makes them highly useful as time-stratigraphic markers. The use of tuffs and other tephra deposits in this manner
6273-491: Is the only alkali metal halide that is poorly soluble in water, and lithium hydroxide is the only alkali metal hydroxide that is not deliquescent . Conversely, lithium perchlorate and other lithium salts with large anions that cannot be polarised are much more stable than the analogous compounds of the other alkali metals, probably because Li has a high solvation energy . This effect also means that most simple lithium salts are commonly encountered in hydrated form, because
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6426-489: Is the use of shell or coral inlaid with obsidian to represent eyes. Rapa Nui traditional music consists of choral singing and chanting accompanied by instruments including conch shell trumpets, percussive dancers, accordions, and kauaha, a percussion instrument created from the jaw bone of a horse. Modern Rapanui music has had Latin American influences creating new genres such as the Rapa Nui style of tango. Matato'a , one of
6579-429: Is very easily excited. Indeed, these flame test colours are the most common way of identifying them since all their salts with common ions are soluble. The ns configuration also results in the alkali metals having very large atomic and ionic radii , as well as very high thermal and electrical conductivity . Their chemistry is dominated by the loss of their lone valence electron in the outermost s-orbital to form
6732-720: The Rochlitz Porphyr , can be seen in the Mannerist -style sculpted portal outside the chapel entrance in Colditz Castle . The trade name Rochlitz Porphyr is the traditional designation for a dimension stone of Saxony with an architectural history over 1,000 years in Germany. The quarries are located near Rochlitz. Yucca Mountain nuclear waste repository , a U.S. Department of Energy terminal storage facility for spent nuclear reactor and other radioactive waste,
6885-622: The Carboniferous strata, and among the still older rocks of the Lake District, the southern uplands of Scotland, and Wales. They are black, dark green, or red in colour; vary greatly in coarseness, some being full of round spongy bombs a foot or more in diameter; and being often submarine, may contain shale, sandstone, grit, and other sedimentary material, and are occasionally fossiliferous. Recent basaltic tuffs are found in Iceland ,
7038-538: The Curie Institute in Paris, France discovered francium in 1939 by purifying a sample of actinium-227 , which had been reported to have a decay energy of 220 keV . However, Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one that was separated during purification, but emerged again out of
7191-570: The Faroe Islands , Jan Mayen , Sicily, the Hawaiian Islands , Samoa , etc. When weathered, they are filled with calcite, chlorite, serpentine , and especially where the lavas contain nepheline or leucite , are often rich in zeolites , such as analcite , prehnite , natrolite , scolecite , chabazite , heulandite , etc. Ultramafic tuffs are extremely rare; their characteristic is the abundance of olivine or serpentine and
7344-601: The Lava Creek Tuff erupted from Yellowstone Caldera in Wyoming 631,000 years ago. This tuff had an original volume of at least 1,000 cubic kilometers (240 cu mi). Lava Creek tuff is known to be at least 1000 times as large as the deposits of the 1980 eruption of Mount St. Helens , and it had a Volcanic Explosivity Index (VEI) of 8, greater than any eruption known in the last 10,000 years. Ash flow tuffs cover 7,000 square kilometers (2,700 sq mi) of
7497-461: The North Island of New Zealand and about 100,000 square kilometers (39,000 sq mi) of Nevada . Ash flow tuffs are the only volcanic product with volumes rivaling those of flood basalts . The Tioga Bentonite of the northeastern United States varies in composition from crystal tuff to tuffaceous shale. It was deposited as ash carried by wind that fell out over the sea and settled to
7650-527: The Pentland Hills , the Cheviots , and many other districts of Great Britain , ancient rocks of exactly similar nature are abundant. In color, they are red or brown; their scoriae fragments are of all sizes from huge blocks down to minute granular dust. The cavities are filled with many secondary minerals, such as calcite , chlorite , quartz, epidote , or chalcedony; in microscopic sections, though,
7803-757: The Rhine (at Siebengebirge ), in Ischia and near Naples . Trachyte-carbonatite tuffs have been identified in the East African Rift . Alkaline crystal tuffs have been reported from Rio de Janeiro . Andesitic tuffs are exceedingly common. They occur along the whole chain of the Cordilleras and Andes , in the West Indies , New Zealand, Japan, etc. In the Lake District , North Wales, Lorne ,
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#17327810877457956-434: The boiling point of a substance (in liquid state) is the point where the vapour pressure of the liquid equals the environmental pressure surrounding the liquid and all the liquid changes state to gas. As a metal is heated to its melting point, the metallic bonds keeping the atoms in place weaken so that the atoms can move around, and the metallic bonds eventually break completely at the metal's boiling point. Therefore,
8109-464: The electrides , which are salts with trapped electrons acting as anions. A particularly striking example of an alkalide is "inverse sodium hydride ", H Na (both ions being complexed ), as opposed to the usual sodium hydride, Na H : it is unstable in isolation, due to its high energy resulting from the displacement of two electrons from hydrogen to sodium, although several derivatives are predicted to be metastable or stable. In aqueous solution,
8262-407: The formation and evolution of the solar system . In turn, the natural history of the Earth caused parts of this planet to have differing concentrations of the elements. The mass of the Earth is approximately 5.98 × 10 kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with
8415-413: The halogens to form the alkali metal halides , which are white ionic crystalline compounds that are all soluble in water except lithium fluoride (LiF). The alkali metals also react with water to form strongly alkaline hydroxides and thus should be handled with great care. The heavier alkali metals react more vigorously than the lighter ones; for example, when dropped into water, caesium produces
8568-422: The octaves of music, where notes an octave apart have similar musical functions. His version put all the alkali metals then known (lithium to caesium), as well as copper, silver, and thallium (which show the +1 oxidation state characteristic of the alkali metals), together into a group. His table placed hydrogen with the halogens . After 1869, Dmitri Mendeleev proposed his periodic table placing lithium at
8721-404: The s-block of the periodic table . 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. This family of elements
8874-507: The +1 oxidation state, due to the ease of ionising this electron and the very high second ionisation energy. Most of the chemistry has been observed only for the first five members of the group. The chemistry of francium is not well established due to its extreme radioactivity ; thus, the presentation of its properties here is limited. What little is known about francium shows that it is very close in behaviour to caesium, as expected. The physical properties of francium are even sketchier because
9027-447: The 18-column table, the group IB elements were moved to their current position in the d-block , while alkali metals were left in group IA . Later the group's name was changed to group 1 in 1988. The trivial name "alkali metals" comes from the fact that the hydroxides of the group 1 elements are all strong alkalis when dissolved in water. There were at least four erroneous and incomplete discoveries before Marguerite Perey of
9180-579: The 26 monoisotopic elements that have only a single stable isotope, all but one have an odd atomic number and all but one also have an even number of neutrons. Beryllium is the single exception to both rules, due to its low atomic number. All of the alkali metals except lithium and caesium have at least one naturally occurring radioisotope : sodium-22 and sodium-24 are trace radioisotopes produced cosmogenically , potassium-40 and rubidium-87 have very long half-lives and thus occur naturally, and all isotopes of francium are radioactive . Caesium
9333-450: The 6p electrons of francium. All the alkali metals have odd atomic numbers; hence, their isotopes must be either odd–odd (both proton and neutron number are odd) or odd–even ( proton number is odd, but neutron number is even). Odd–odd nuclei have even mass numbers , whereas odd–even nuclei have odd mass numbers. Odd–odd primordial nuclides are rare because most odd–odd nuclei are highly unstable with respect to beta decay , because
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#17327810877459486-554: The Big Bang could only produce trace quantities of lithium, beryllium and boron due to the absence of a stable nucleus with 5 or 8 nucleons , and stellar nucleosynthesis could only pass this bottleneck by the triple-alpha process , fusing three helium nuclei to form carbon , and skipping over those three elements. The Earth formed from the same cloud of matter that formed the Sun, but the planets acquired different compositions during
9639-519: The Earth's crust measured by weight, making it the sixth most abundant element overall and the most abundant alkali metal. Potassium makes up approximately 1.5% of the Earth's crust and is the seventh most abundant element. 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. Other solid deposits include halite , amphibole , cryolite , nitratine , and zeolite . Many of these solid deposits occur as
9792-445: The Earth's surface because they combine readily with oxygen and so associate strongly with silica , forming relatively low-density minerals that do not sink down into the Earth's core. Potassium, rubidium and caesium are also incompatible elements due to their large ionic radii . Sodium and potassium are very abundant on Earth, both being among the ten most common elements in Earth's crust ; sodium makes up approximately 2.6% of
9945-503: The Rapa Nui and the Chilean government are focused on preserving and restoring the statues, including denoting an area that includes many of the statues, Rapa Nui National Park , as a World Heritage site. The Rapa Nui have historically made feather headdresses, bark cloth, wood carvings, and stone carvings. Adzes, blunt round stones, were used to complete stone images and wood carvings. A distinguishing characteristic of Rapa Nui statues
10098-441: The Rapa Nui culture is the moai , the 887 human figures carved from rock between 1250 and 1500 CE and transported throughout Easter Island. The moai were believed to be the living faces of ancestors and had all been toppled by 1868. The moai rest on large stone platforms called ahu , the most famous of which are Ahu Tongariki , the largest ahu, and Ahu Vinapu . Some moai have hats of red volcanic stone known as Pukao . Currently,
10251-427: The Rapa Nui had European and Amerindian contributions to their DNA during or before the early 1800s. Jacob Roggeveen was the first European to record contact with the Rapa Nui. Roggeveen allegedly set sail either in search of Juan Fernández Islands or David's Island but instead arrived at Easter Island on April 5, 1722 ( Easter Sunday ). He remained on the island for about a week. Felipe González de Ahedo visited
10404-407: The Rapa Nui in 1770 and claimed the island for Spain on a document which the islanders wrote on in rongorongo , the now undecipherable Rapa Nui script. James Cook and Jean-François de Galaup, comte de Lapérouse , visited the island for a few days in 1774 and 1786, respectively. The Rapa Nui currently speak Spanish and the traditional Rapa Nui language. The Rapa Nui language, also known as Pascuan,
10557-664: The Tangata manu. The Tangata manu is the mythology of the Birdman religion and cult which had creator god Makemake and competition with eggs to choose the birdman who would remain sacred for five months. More recent Rapa Nui mythology includes the story of the epic battle between the Hanau Epe and the Hanau Momoko. The trans-Neptunian dwarf planet Makemake is named after this creator deity. The best-known aspect of
10710-486: The alkali metal hydroxides to give aluminates, zincates, stannates, and plumbates. Silicon dioxide is acidic, and thus the alkali metal hydroxides can also attack silicate glass . The alkali metals form many intermetallic compounds with each other and the elements from groups 2 to 13 in the periodic table of varying stoichiometries, such as the sodium amalgams with mercury , including Na 5 Hg 8 and Na 3 Hg. Some of these have ionic characteristics: taking
10863-406: The alkali metal ions form aqua ions of the formula [M(H 2 O) n ] , where n is the solvation number. Their coordination numbers and shapes agree well with those expected from their ionic radii. In aqueous solution the water molecules directly attached to the metal ion are said to belong to the first coordination sphere , also known as the first, or primary, solvation shell. The bond between
11016-452: The alkali metals can be readily explained by their having an ns valence electron configuration , which results in weak metallic bonding . Hence, all the alkali metals are soft and have low densities , melting and boiling points , as well as heats of sublimation , vaporisation , and dissociation . They all crystallise in the body-centered cubic crystal structure, and have distinctive flame colours because their outer s electron
11169-440: The alloys with gold, the most electronegative of metals, as an example, NaAu and KAu are metallic, but RbAu and CsAu are semiconductors. NaK is an alloy of sodium and potassium that is very useful because it is liquid at room temperature, although precautions must be taken due to its extreme reactivity towards water and air. The eutectic mixture melts at −12.6 °C. An alloy of 41% caesium, 47% sodium, and 12% potassium has
11322-597: The alpha branching at 0.6%, a figure that she later revised to 1%. The next element below francium ( eka -francium) in the periodic table would be ununennium (Uue), element 119. The synthesis of ununennium was first attempted in 1985 by bombarding a target of einsteinium -254 with calcium -48 ions at the superHILAC accelerator at the Lawrence Berkeley National Laboratory in Berkeley, California. No atoms were identified, leading to
11475-405: The anhydrous forms are extremely hygroscopic : this allows salts like lithium chloride and lithium bromide to be used in dehumidifiers and air-conditioners . Francium is also predicted to show some differences due to its high atomic weight , causing its electrons to travel at considerable fractions of the speed of light and thus making relativistic effects more prominent. In contrast to
11628-453: The areas where such tuffs are prominent. In the ancient rocks of Wales , Charnwood , etc., similar tuffs are known, but in all cases, they are greatly changed by silicification (which has filled them with opal , chalcedony , and quartz) and by devitrification. The frequent presence of rounded corroded quartz crystals, such as occur in rhyolitic lavas, helps to demonstrate their real nature. Welded ignimbrites can be highly voluminous, such as
11781-425: The bare metallic surface of the liquid metal, leaving a positively charged metal surface and negatively charged water ions. The attraction between the charged metal and water ions will rapidly increase the surface area, causing an exponential increase of ionisation. When the repulsive forces within the liquid metal surface exceeds the forces of the surface tension, it vigorously explodes. The hydroxides themselves are
11934-559: The best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks , of which caesium atomic clocks form the basis of the second. 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 and as an anode in lithium batteries . Sodium, potassium and possibly lithium are essential elements , having major biological roles as electrolytes , and although
12087-477: The bottom. It is Devonian in age and likely came from a vent in central Virginia , where the tuff reaches its maximum thickness of about 40 meters (130 ft). Trachyte tuffs contain little or no quartz, but much sanidine or anorthoclase and sometimes oligoclase feldspar, with occasional biotite, augite, and hornblende. In weathering, they often change to soft red or yellow claystones , rich in kaolin with secondary quartz. Recent trachyte tuffs are found on
12240-458: The bulk element has never been observed; hence any data that may be found in the literature are certainly speculative extrapolations. The alkali metals are more similar to each other than the elements in any other group are to each other. Indeed, the similarity is so great that it is quite difficult to separate potassium, rubidium, and caesium, due to their similar ionic radii ; lithium and sodium are more distinct. For instance, when moving down
12393-400: 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. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones. All of
12546-545: The chemist Jöns Jacob Berzelius , detected the presence of a new element while analysing petalite ore . This new element was noted by him to form compounds similar to those of sodium and potassium, though its carbonate and hydroxide were less soluble in water and more alkaline than the other alkali metals. Berzelius gave the unknown material the name lithion / lithina , from the Greek word λιθoς (transliterated as lithos , meaning "stone"), to reflect its discovery in
12699-399: The chlorine because the effective nuclear charge on the outer electrons is +7 in chlorine but is only +1 in sodium. The electron pair is attracted so close to the chlorine atom that they are practically transferred to the chlorine atom (an ionic bond ). However, if the sodium atom was replaced by a lithium atom, the electrons will not be attracted as close to the chlorine atom as before because
12852-430: The clear trends going from lithium to caesium, such as the first ionisation energy, electron affinity, and anion polarisability, though due to the paucity of known data about francium many sources give extrapolated values, ignoring that relativistic effects make the trend from lithium to caesium become inapplicable at francium. Some of the few properties of francium that have been predicted taking relativity into account are
13005-406: The composition of the ash from which they formed. Ash from high-silica volcanism, particularly in ash flows, consists mainly of shards of volcanic glass , and tuff formed predominantly from glass shards is described as vitric tuff. The glass shards are typically either irregular in shape or are roughly triangular with convex sides. They are the shattered walls of countless small bubbles that formed in
13158-684: The corresponding lavas and sills . Some chlorite-schists also are probably altered beds of volcanic tuff. The "Schalsteins" of Devon and Germany include many cleaved and partly recrystallized ash-beds, some of which still retain their fragmental structure, though their lapilli are flattened and drawn out. Their steam cavities are usually filled with calcite, but sometimes with quartz. The more completely altered forms of these rocks are platy, green chloritic schists; in these, however, structures indicating their original volcanic nature only sparingly occur. These are intermediate stages between cleaved tuffs and crystalline schists. The primary economic value of tuff
13311-442: The date of arrival was estimated to be around 700–800 CE, but more-recent evidence from radiocarbon dating supports an arrival date as late as 1200 CE. The Rapa Nui People have been found to be of Polynesian origin through genetic analysis of mitochondrial DNA of pre-historic skeletons. Genetic analysis performed by Erik Thorsby and other geneticists in 2007 revealed genetic markers of European and Amerindian origin that suggest that
13464-418: The decay products are even–even, and are therefore more strongly bound, due to nuclear pairing effects . Due to the great rarity of odd–odd nuclei, almost all the primordial isotopes of the alkali metals are odd–even (the exceptions being the light stable isotope lithium-6 and the long-lived radioisotope potassium-40). For a given odd mass number, there can be only a single beta-stable nuclide , since there
13617-404: The degree of welding. The base of a cooling unit is typically unwelded due to chilling from the underlying cold surface, and the degree of welding and of secondary reactions from fluids in the flow increases upwards towards the center of the flow. Welding decreases towards the top of the cooling unit, where the unit cools more rapidly. The intensity of welding may also decrease towards areas in which
13770-407: The delocalised electrons and hence the metallic bond becomes weaker so that the metal can more easily melt and boil, thus lowering the melting and boiling points. The increased nuclear charge is not a relevant factor due to the shielding effect. The alkali metals all have the same crystal structure ( body-centred cubic ) and thus the only relevant factors are the number of atoms that can fit into
13923-424: The deposit is thinner, and with distance from source. Cooler pyroclastic flows are unwelded and the ash sheets deposited by them are relatively unconsolidated. However, cooled volcanic ash can quickly become lithified because it usually has a high content of volcanic glass. This is a thermodynamically unstable material that reacts rapidly with ground water or sea water, which leaches alkali metals and calcium from
14076-431: 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 minute traces in nature as an intermediate step in some obscure side branches of the natural decay chains . Experiments have been conducted to attempt
14229-400: The distance from the most loosely held electron from the nucleus, which is always an outer electron in main group elements . The first two factors change the effective nuclear charge the most loosely held electron feels. Since the outermost electron of alkali metals always feels the same effective nuclear charge (+1), the only factor which affects the first ionisation energy is the distance from
14382-408: The divalent lanthanides europium and ytterbium , are pale yellow, though the colour is much less prominent than it is for caesium. Their lustre tarnishes rapidly in air due to oxidation. All the alkali metals are highly reactive and are never found in elemental forms in nature. Because of this, they are usually stored in mineral oil or kerosene (paraffin oil). They react aggressively with
14535-507: The electron affinity (47.2 kJ/mol) and the enthalpy of dissociation of the Fr 2 molecule (42.1 kJ/mol). The CsFr molecule is polarised as Cs Fr , showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium. Additionally, francium superoxide (FrO 2 ) is expected to have significant covalent character, unlike the other alkali metal superoxides, because of bonding contributions from
14688-517: The elements with even atomic numbers adjacent to them (the noble gases and the alkaline earth metals ) in the Solar System. The heavier alkali metals are also less abundant than the lighter ones as the alkali metals from rubidium onward can only be synthesised in supernovae and not in stellar nucleosynthesis . Lithium is also much less abundant than sodium and potassium as it is poorly synthesised in both Big Bang nucleosynthesis and in stars:
14841-586: The environment during nearly all nuclear weapon tests and some nuclear accidents , most notably the Goiânia accident and the Chernobyl disaster . As of 2005, caesium-137 is the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant . Its chemical properties as one of the alkali metals make it one of the most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to
14994-404: The exception of hydrogen. This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability. All the alkali metals have odd atomic numbers and they are not as common as
15147-429: The falling melting and boiling points of the alkali metals indicate that the strength of the metallic bonds of the alkali metals decreases down the group. This is because metal atoms are held together by the electromagnetic attraction from the positive ions to the delocalised electrons. As the atoms increase in size going down the group (because their atomic radius increases), the nuclei of the ions move further away from
15300-489: The first elements to be discovered using the spectroscope , invented in 1859 by Robert Bunsen and Gustav Kirchhoff . The next year, they discovered caesium in the mineral water from Bad Dürkheim , Germany. Their discovery of rubidium came the following year in Heidelberg , Germany, finding it in the mineral lepidolite . The names of rubidium and caesium come from the most prominent lines in their emission spectra :
15453-413: The first ionisation energies and atomisation energies of the alkali metals. Because the first ionisation energy of the alkali metals decreases down the group, it is easier for the outermost electron to be removed from the atom and participate in chemical reactions , thus increasing reactivity down the group. The atomisation energy measures the strength of the metallic bond of an element, which falls down
15606-413: The fundamental difference of sodium and potassium salts in 1702, and Henri-Louis Duhamel du Monceau was able to prove this difference in 1736. The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus Antoine Lavoisier did not include either alkali in his list of chemical elements in 1789. Pure potassium
15759-424: The giant sculptures called moai . Over the past decade, Rapa Nui activists have been fighting for self-determination and sovereignty over their lands. Protests in 2010 and 2011 by the indigenous Rapa Nui on Easter Island, objecting to the creation of a marine park and reserve, have led to clashes with Chilean police . Rapa Nui are believed to have settled Easter Island between 300 and 1200 CE. Previously,
15912-443: The glass. New minerals, such as zeolites , clays , and calcite , crystallize from the dissolved substances and cement the tuff. Tuffs are further classified by their depositional environment, such as lacustrine tuff, subaerial tuff, or submarine tuff, or by the mechanism by which the ash was transported, such as fallout tuff or ash flow tuff. Reworked tuffs, formed by erosion and redeposition of ash deposits, are usually described by
16065-578: The green slates of the English Lake District are finely cleaved ashes. In Charnwood Forest also, the tuffs are slaty and cleaved. The green color is due to the large development of chlorite. Among the crystalline schists of many regions, green beds or green schists occur, which consist of quartz, hornblende, chlorite or biotite, iron oxides , feldspar, etc., and are probably recrystallized or metamorphosed tuffs. They often accompany masses of epidiorite and hornblende – schists which are
16218-433: The group as the atoms increase in radius and thus the metallic bond must increase in length, making the delocalised electrons further away from the attraction of the nuclei of the heavier alkali metals. Adding the atomisation and first ionisation energies gives a quantity closely related to (but not equal to) the activation energy of the reaction of an alkali metal with another substance. This quantity decreases going down
16371-442: The group, and so does the activation energy; thus, chemical reactions can occur faster and the reactivity increases down the group. Electronegativity is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density ) towards itself. If the bond between sodium and chlorine in sodium chloride were covalent , the pair of shared electrons would be attracted to
16524-426: The group. The ionic radii of the alkali metals are much smaller than their atomic radii. This is because the outermost electron of the alkali metals is in a different electron shell than the inner electrons, and thus when it is removed the resulting atom has one fewer electron shell and is smaller. Additionally, the effective nuclear charge has increased, and thus the electrons are attracted more strongly towards
16677-553: The high water solubility of its salts, and is taken up by the body, which mistakes it for its essential congeners sodium and potassium. The alkali metals are more similar to each other than the elements in any other group are to each other. For instance, when moving down the table, all known alkali metals show increasing atomic radius , decreasing electronegativity , increasing reactivity , and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their densities increase when moving down
16830-421: The initial reaction of the metal with water (which tends to happen mostly under water). The alkali metal hydroxides are the most basic known hydroxides. Recent research has suggested that the explosive behavior of alkali metals in water is driven by a Coulomb explosion rather than solely by rapid generation of hydrogen itself. All alkali metals melt as a part of the reaction with water. Water molecules ionise
16983-509: The island and the diseases that commonly came with them like smallpox , with several researchers having instead noted that pre-colonial Rapa Nui society was rather stable. Agriculture on Easter Island shows signs of intensification before European arrival, necessary because of its climate which had an excess of wind and a low amount of rainfall for the area. Archaeological finds show a multitude of composting pits and irrigation systems. Large boulders were also stacked to serve as barriers against
17136-414: The island's trees. The most prominent proponent of this explanation is Jared Diamond who proposes a scenario for the " ecocide " on Easter Island in his 2005 book Collapse . This idea that Rapa Nui society collapsed came out of the imbalance between general resources present on the island, mainly population, timber and food sources, and the energy- and resource-intensive feat of transporting and raising
17289-481: The last demonstrating the phenomenal degree of their reactivity. Their great power as reducing agents makes them very useful in liberating other metals from their oxides or halides. The second ionisation energy of all of the alkali metals is very high as it is in a full shell that is also closer to the nucleus; thus, they almost always lose a single electron, forming cations. The alkalides are an exception: they are unstable compounds which contain alkali metals in
17442-430: The lithium atom is smaller, making the electron pair more strongly attracted to the closer effective nuclear charge from lithium. Hence, the larger alkali metal atoms (further down the group) will be less electronegative as the bonding pair is less strongly attracted towards them. As mentioned previously, francium is expected to be an exception. Because of the higher electronegativity of lithium, some of its compounds have
17595-584: The magma as dissolved gases rapidly came out of solution. Tuffs formed from ash consisting predominantly of individual crystals are described as crystal tuffs, while those formed from ash consisting predominantly of pulverized rock fragments are described as lithic tuffs. The chemical composition of volcanic ash reflects the entire range of volcanic rock chemistry, from high-silica rhyolitic ash to low-silica basaltic ash, and tuffs are likewise described as rhyolitic, andesitic, basaltic, and so on. The most straightforward way for volcanic ash to move away from
17748-456: The moai. Food resources may have been scarcer than in other areas of Polynesia because of factors like the cooler climate, lack of rainfall in comparison to other islands in the area, high winds and a lack of biodiversity, leading to common Polynesian crops not faring as well as they would in other areas of the Pacific. A source of good timber is also currently noticeably absent from the island,
17901-426: The most basic hydroxides known, reacting with acids to give salts and with alcohols to give oligomeric alkoxides . They easily react with carbon dioxide to form carbonates or bicarbonates , or with hydrogen sulfide to form sulfides or bisulfides , and may be used to separate thiols from petroleum. They react with amphoteric oxides: for example, the oxides of aluminium , zinc , tin , and lead react with
18054-400: The most electropositive alkali metal, despite the difficulty of ionising it in the gas phase. The stable alkali metals are all silver-coloured metals except for caesium, which has a pale golden tint: it is one of only three metals that are clearly coloured (the other two being copper and gold). Additionally, the heavy alkaline earth metals calcium , strontium , and barium , as well as
18207-413: The most famous musical groups on the island, promotes traditional styles of dance and music. Like in other Polynesian islands, tattoos and body paintings had a fundamentally spiritual connotation. In some cases the tattoos were considered a receptor for divine strength or mana. They were manifestations of the Rapa Nui culture. Priests, warriors and chiefs had more tattoos than the rest of the population, as
18360-653: The nature of the original lava can nearly always be made out from the shapes and properties of the little crystals which occur in the decomposed glassy base. Even in the smallest details, these ancient tuffs have a complete resemblance to the modern ash beds of Cotopaxi , Krakatoa , and Mont Pelé. Mafic volcanism typically takes the form of Hawaiian eruptions that are nonexplosive and produce little ash. However, interaction between basaltic magma and groundwater or sea water results in hydromagmatic explosions that produce abundant ash. These deposit ash cones that subsequently can become cemented into tuff cones. Diamond Head, Hawaii ,
18513-418: The nucleus and the ionic radius decreases. The first ionisation energy of an element or molecule is the energy required to move the most loosely held electron from one mole of gaseous atoms of the element or molecules to form one mole of gaseous ions with electric charge +1. The factors affecting the first ionisation energy are the nuclear charge , the amount of shielding by the inner electrons and
18666-411: The nucleus, increasing its first ionisation energy slightly beyond that of caesium. The second ionisation energy of the alkali metals is much higher than the first as the second-most loosely held electron is part of a fully filled electron shell and is thus difficult to remove. The reactivities of the alkali metals increase going down the group. This is the result of a combination of two factors:
18819-445: The octahedral [Na(H 2 O) 6 ] ion. While it was previously thought that the heavier alkali metals also formed octahedral hexaaqua ions, it has since been found that potassium and rubidium probably form the [K(H 2 O) 8 ] and [Rb(H 2 O) 8 ] ions, which have the square antiprismatic structure, and that caesium forms the 12-coordinate [Cs(H 2 O) 12 ] ion. The chemistry of lithium shows several differences from that of
18972-478: The only naturally occurring isotope of francium, is the product of the alpha decay of actinium-227 and can be found in trace amounts in uranium minerals. In a given sample of uranium, there is estimated to be only one francium atom for every 10 uranium atoms. It has been calculated that there are at most 30 grams of francium in the earth's crust at any time, due to its extremely short half-life of 22 minutes. The physical and chemical properties of
19125-427: The only three metals in the periodic table that are less dense than water: in fact, lithium is the least dense known solid at room temperature . The alkali metals form complete series of compounds with all usually encountered anions, which well illustrate group trends. These compounds can be described as involving the alkali metals losing electrons to acceptor species and forming monopositive ions. This description
19278-494: The original people of Easter Island make up about 60% of the current Easter Island population and have a significant portion of their population residing in mainland Chile . They speak both the traditional Rapa Nui language and the primary language of Chile, Spanish . At the 2017 census there were 7,750 island inhabitants—almost all living in the village of Hanga Roa on the sheltered west coast. As of 2011, Rapa Nui's main source of income derived from tourism , which focuses on
19431-490: The other alkali metals are not essential, they also have various effects on the body, both beneficial and harmful. Sodium compounds have been known since ancient times; salt ( sodium chloride ) has been an important commodity in human activities. While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence which led him to suggest
19584-488: The outermost electron to the nucleus. Since this distance increases down the group, the outermost electron feels less attraction from the nucleus and thus the first ionisation energy decreases. This trend is broken in francium due to the relativistic stabilisation and contraction of the 7s orbital, bringing francium's valence electron closer to the nucleus than would be expected from non-relativistic calculations. This makes francium's outermost electron feel more attraction from
19737-471: The pure actinium -227. Various tests eliminated the possibility of the unknown element being thorium , radium , lead, bismuth , or thallium . The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, caused by the alpha decay of actinium-227. Perey then attempted to determine the proportion of beta decay to alpha decay in actinium-227. Her first test put
19890-486: The radioactivity still left from the Chernobyl accident . Caesium-137 undergoes high-energy beta decay and eventually becomes stable barium-137 . It is a strong emitter of gamma radiation. Caesium-137 has a very low rate of neutron capture and cannot be feasibly disposed of in this way, but must be allowed to decay. Caesium-137 has been used as a tracer in hydrologic studies, analogous to the use of tritium . Small amounts of caesium-134 and caesium-137 were released into
20043-408: The ratios between the densities of the alkali metals can then be calculated. The resultant trend is that the densities of the alkali metals increase down the table, with an exception at potassium. Due to having the lowest atomic weight and the largest atomic radius of all the elements in their periods, the alkali metals are the least dense metals in the periodic table. Lithium, sodium, and potassium are
20196-410: The remaining 1.2% consisting of trace amounts of other elements. Due to planetary differentiation , the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements. The alkali metals, due to their high reactivity, do not occur naturally in pure form in nature. They are lithophiles and therefore remain close to
20349-596: The rest of the group as the small Li cation polarises anions and gives its compounds a more covalent character. Lithium and magnesium have a diagonal relationship due to their similar atomic radii, so that they show some similarities. For example, lithium forms a stable nitride , a property common among all the alkaline earth metals (magnesium's group) but unique among the alkali metals. In addition, among their respective groups, only lithium and magnesium form organometallic compounds with significant covalent character (e.g. Li Me and MgMe 2 ). Lithium fluoride
20502-400: The result of the formation of contact ion pairs , and the higher solvation numbers may be interpreted in terms of water molecules that approach [Li(H 2 O) 4 ] through a face of the tetrahedron, though molecular dynamic simulations may indicate the existence of an octahedral hexaaqua ion. There are also probably six water molecules in the primary solvation sphere of the sodium ion, forming
20655-647: The scarcity or absence of feldspar and quartz . Occurrences of ultramafic tuff include surface deposits of kimberlite at maars in the diamond -fields of southern Africa and other regions. The principal variety of kimberlite is a dark bluish-green, serpentine-rich breccia (blue-ground) which, when thoroughly oxidized and weathered, becomes a friable brown or yellow mass (the "yellow-ground"). These breccias were emplaced as gas–solid mixtures and are typically preserved and mined in diatremes that form intrusive pipe-like structures. At depth, some kimberlite breccias grade into root zones of dikes made of unfragmented rock. At
20808-460: The similar substance caustic soda (NaOH, lye) by a similar technique, demonstrating the elements, and thus the salts, to be different. Petalite ( Li Al Si 4 O 10 ) was discovered in 1800 by the Brazilian chemist José Bonifácio de Andrada in a mine on the island of Utö, Sweden . However, it was not until 1817 that Johan August Arfwedson , then working in the laboratory of
20961-479: The sole domestic animal, though the "chicken coops" carved of stone which still dot the fields of the island were most likely tombs from which the chickens obtained calcium and phosphorus in the form of bone meal. Alkali metal Legend The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1 , which lies in
21114-407: The surface . These violent explosions produce particles of material that can then fly from the volcano. Solid particles smaller than 2 mm in diameter ( sand-sized or smaller) are called volcanic ash. Volcanic ash is further divided into fine ash, with particle sizes smaller than 0.0625 mm in diameter, and coarse ash, with particle sizes between 0.0625 mm and 2 mm in diameter. Tuff
21267-418: The surface can be transported as mud flows ( lahars ) when mingled with water from rainfall or through eruption into a body of water or ice. Particles of volcanic ash that are sufficiently hot will weld together after settling to the surface, producing a welded tuff . Welding requires temperatures in excess of 600 °C (1,100 °F). If the rock contains scattered, pea-sized fragments or fiamme in it, it
21420-567: The surface, ultramafic tuffs may occur in maar deposits. Because kimberlites are the most common igneous source of diamonds, the transitions from maar to diatreme to root-zone dikes have been studied in detail. Diatreme- facies kimberlite is more properly called an ultramafic breccia rather than a tuff. Komatiite tuffs are found, for example, in the greenstone belts of Canada and South Africa. In course of time, changes other than weathering may overtake tuff deposits. Sometimes, they are involved in folding and become sheared and cleaved . Many of
21573-498: The synthesis of element 119 , which is likely to be the next member of the group; none were successful. 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
21726-420: The table, all known alkali metals show increasing atomic radius , decreasing electronegativity , increasing reactivity , and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their densities increase when moving down the table, with the exception that potassium is less dense than sodium. One of the very few properties of the alkali metals that does not display
21879-402: The table, with the exception that potassium is less dense than sodium. The atomic radii of the alkali metals increase going down the group. Because of the shielding effect , when an atom has more than one electron shell , each electron feels electric repulsion from the other electrons as well as electric attraction from the nucleus. In the alkali metals, the outermost electron only feels
22032-412: The tallest extant plant life averaging around 7 feet. Although Easter Island currently has only 48 different kinds of plants as evidenced by botanical surveys of the island, it once possessed many more, shown through pollen analysis conducted on sediment layers from swamps or ponds. From these samples, 22 no longer present on the island were shown to have existed at some time there. These plants included
22185-408: The top of a group with sodium, potassium, rubidium, caesium, and thallium. Two years later, Mendeleev revised his table, placing hydrogen in group 1 above lithium, and also moving thallium to the boron group . In this 1871 version, copper, silver, and gold were placed twice, once as part of group IB , and once as part of a "group VIII" encompassing today's groups 8 to 11. After the introduction of
22338-422: The transport agent, such as aeolian tuff or fluvial tuff. Tuffs have the potential to be deposited wherever explosive volcanism takes place, and so have a wide distribution in location and age. Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with quartz , alkali feldspar , biotite , etc. Iceland, Lipari, Hungary, the Basin and Range of the American southwest, and New Zealand are among
22491-465: The trend of decreasing electronegativities and ionisation energies of the alkali metals, francium's electronegativity and ionisation energy are predicted to be higher than caesium's due to the relativistic stabilisation of the 7s electrons; also, its atomic radius is expected to be abnormally low. Thus, contrary to expectation, caesium is the most reactive of the alkali metals, not francium. All known physical properties of francium also deviate from
22644-578: The vent is as ash clouds that are part of an eruption column . These fall to the surface as fallout deposits that are characteristically well-sorted and tend to form a blanket of uniform thickness across terrain. Column collapse results in a more spectacular and destructive form of transport, which takes the form of pyroclastic flows and surges that characteristically are poorly sorted and pool in low terrain. Surge deposits sometimes show sedimentary structures typical of high-velocity flow, such as dunes and antidunes . Volcanic ash already deposited on
22797-429: The water first, breaking the hydrogen bonds in the water and producing hydrogen gas; this takes place faster for the more reactive heavier alkali metals. Second, the heat generated by the first part of the reaction often ignites the hydrogen gas, causing it to burn explosively into the surrounding air. This secondary hydrogen gas explosion produces the visible flame above the bowl of water, lake or other body of water, not
22950-446: The wind. In the fields, a system of agriculture called lithic mulch was employed. In this method, farmers would lay rocks out in patterns in their fields, forcing the plants to grow in certain areas. This method is known to increase soil moisture while decreasing soil erosion from wind, effectively combating the climate conditions. Crops grown on Easter Island included sweet potatoes, yams, taro , bananas and sugarcane. Chickens were
23103-491: Was also thought to be radioactive in the early 20th century, although it has no naturally occurring radioisotopes. (Francium had not been discovered yet at that time.) The natural long-lived radioisotope of potassium, potassium-40, makes up about 0.012% of natural potassium, and thus natural potassium is weakly radioactive. This natural radioactivity became a basis for a mistaken claim of the discovery for element 87 (the next alkali metal after caesium) in 1925. Natural rubidium
23256-502: Was first isolated in 1807 in England by Humphry Davy , who derived it from caustic potash (KOH, potassium hydroxide) by the use of electrolysis of the molten salt with the newly invented voltaic pile . Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium's extreme reactivity. Potassium was the first metal that was isolated by electrolysis. Later that same year, Davy reported extraction of sodium from
23409-741: Was made out of natural products, primarily from the burning of Ti leaves ( Cordyline terminalis ) and sugar cane. Pascuense cuisine, otherwise known as Easter Island cuisine or Rapa Nui cuisine incorporates the influences of the indigenous Rapa Nui people and Latin America. Notable ingredients include seafood such as fish, octopus (heke), eel, sea snails (pipi) and crustaceans (lobster), as well as sweet potato, taro, banana, pineapple, coconut, pumpkin, and poultry, pork and lamb meat.[1] Traditional foods include umu, meat, fish, vegetables and fruit wrapped in banana leaves and roasted in umu pae – an earth oven. Po'e, pudding made of mashed bananas, pumpkin and flour
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