Split (1)

train · 617k rows

text stringlengths 2 132k	source dict
converters when magnetic fields are also involved. Studies conducted in wind tunnels involve most of the time low atmospheric pressure similar to an altitude of 20–50 km, typical of hypersonic flight, where the electrical conductivity of air is higher, hence non-thermal weakly ionized plasmas can be easily produced wit...	{ "page_id": 6161283, "source": null, "title": "Nonthermal plasma" }
set-up, the main role of the plasma is to alter the gas composition fed to the catalytic reactor. In a PEC system, synergistic effects are greater since short-lived excited species are formed near the catalyst surface. The way the catalyst is inserted in the PEC reactor influence the overall performance. It can be plac...	{ "page_id": 6161283, "source": null, "title": "Nonthermal plasma" }
a catalyst. Presence of new gas phase species. In a plasma discharge a wide range of new species is produced allowing the catalyst to be exposed to them. Ions, vibrationally and rotationally excited species do not affect the catalyst since they lose charge and the additional energy they possess when they reach a solid ...	{ "page_id": 6161283, "source": null, "title": "Nonthermal plasma" }
the presence of a dielectric material inside the discharge region and do not necessarily require the presence of a catalyst. == See also == Anisothermal plasma Gliding Arc Plasmatron == References ==	{ "page_id": 6161283, "source": null, "title": "Nonthermal plasma" }
Actinium is a chemical element; it has symbol Ac and atomic number 89. It was discovered by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. The actinide series, a set of 15 element...	{ "page_id": 899, "source": null, "title": "Actinium" }
as similar to titanium and (in 1900) as similar to thorium. Friedrich Oskar Giesel found in 1902 a substance similar to lanthanum and called it "emanium" in 1904. After a comparison of the substances' half-lives determined by Debierne, Harriet Brooks in 1904, and Otto Hahn and Otto Sackur in 1905, Debierne's chosen nam...	{ "page_id": 899, "source": null, "title": "Actinium" }
used in abbreviations of other compounds that have nothing to do with actinium, such as acetyl, acetate and sometimes acetaldehyde. == Properties == Actinium is a soft, silvery-white, radioactive, metallic element. Its estimated shear modulus is similar to that of lead. Owing to its strong radioactivity, actinium glows...	{ "page_id": 899, "source": null, "title": "Actinium" }
known tripositive ions and its first coordination sphere contains approximately 10.9 ± 0.5 water molecules. == Chemical compounds == Due to actinium's intense radioactivity, only a limited number of actinium compounds are known. These include: AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3, AcPO4 and Ac(NO3)3. Th...	{ "page_id": 899, "source": null, "title": "Actinium" }
trichloride with ammonium hydroxide at 1,000 °C (1,830 °F). However, in contrast to the oxyfluoride, the oxychloride could well be synthesized by igniting a solution of actinium trichloride in hydrochloric acid with ammonia. Reaction of aluminium bromide and actinium oxide yields actinium tribromide: Ac2O3 + 2 AlBr3 → ...	{ "page_id": 899, "source": null, "title": "Actinium" }
through alpha decay. Actinium also has two known meta states. The most significant isotopes for chemistry are 225Ac, 227Ac, and 228Ac. Purified 227Ac comes into equilibrium with its decay products after about a half of year. It decays according to its 21.772-year half-life emitting mostly beta (98.62%) and some alpha p...	{ "page_id": 899, "source": null, "title": "Actinium" }
impractical. The most concentrated actinium sample prepared from raw material consisted of 7 micrograms of 227Ac in less than 0.1 milligrams of La2O3, and complete separation was never achieved. Instead, actinium is prepared, in milligram amounts, by the neutron irradiation of 226Ra in a nuclear reactor. Ra 88 226 + n ...	{ "page_id": 899, "source": null, "title": "Actinium" }
in vacuum at a temperature between 1,100 and 1,300 °C (2,010 and 2,370 °F). Higher temperatures resulted in evaporation of the product and lower ones lead to an incomplete transformation. Lithium was chosen among other alkali metals because its fluoride is most volatile. == Applications == Owing to its scarcity, high p...	{ "page_id": 899, "source": null, "title": "Actinium" }
is the final product in the decay chains of several other candidate isotopes, namely 227Th, 228Th, and 230U. Not only 225Ac itself, but also its daughters, emit alpha particles which kill cancer cells in the body. The major difficulty with application of 225Ac was that intravenous injection of simple actinium complexes...	{ "page_id": 899, "source": null, "title": "Actinium" }
toward the sea bottom. This occurs because of the mixing processes which raise some additional 227Ac from the sea bottom. Thus analysis of both 231Pa and 227Ac depth profiles allows researchers to model the mixing behavior. There are theoretical predictions that AcHx hydrides (in this case with very high pressure) are ...	{ "page_id": 899, "source": null, "title": "Actinium" }
Americium is a synthetic chemical element; it has symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element europium and was thus named after the Americas by analogy. Americium was first produced in 1944 by the group of ...	{ "page_id": 900, "source": null, "title": "Americium" }
it was first intentionally synthesized, isolated and identified in late autumn 1944, at the University of California, Berkeley, by Glenn T. Seaborg, Leon O. Morgan, Ralph A. James, and Albert Ghiorso. They used a 60-inch cyclotron at the University of California, Berkeley. The element was chemically identified at the M...	{ "page_id": 900, "source": null, "title": "Americium" }
two neutrons. It decays by emission of a α-particle to 237Np; the half-life of this decay was first determined as 510±20 years but then corrected to 432.2 years. Pu 94 239 → ( n , γ ) Pu 94 240 → ( n , γ ) Pu 94 241 → 14.35 yr β − Am 95 241 ( → 432.2 yr α Np 93 237 ) {\displaystyle {\ce {^{239}_{94}Pu ->[{\ce {(n,\gamm...	{ "page_id": 900, "source": null, "title": "Americium" }
micrograms were not prepared until 1951 by reduction of americium(III) fluoride with barium metal in high vacuum at 1100 °C. == Occurrence == The longest-lived and most common isotopes of americium, 241Am and 243Am, have half-lives of 432.2 and 7,370 years, respectively. Therefore, any primordial americium (americium t...	{ "page_id": 900, "source": null, "title": "Americium" }
times higher concentration of americium inside sandy soil particles than in the water present in the soil pores; an even higher ratio was measured in loam soils. Americium is produced mostly artificially in small quantities, for research purposes. A tonne of spent nuclear fuel contains about 100 grams of various americ...	{ "page_id": 900, "source": null, "title": "Americium" }
β − Pu 94 239 {\displaystyle {\ce {^{238}_{92}U ->[{\ce {(n,\gamma)}}] ^{239}_{92}U ->[\beta^-][23.5 \ {\ce {min}}] ^{239}_{93}Np ->[\beta^-][2.3565 \ {\ce {d}}] ^{239}_{94}Pu}}} The capture of two neutrons by 239Pu (a so-called (n,γ) reaction), followed by a β-decay, results in 241Am: Pu 94 239 → 2 ( n , γ ) Pu 94 241...	{ "page_id": 900, "source": null, "title": "Americium" }
americium can be separated. In a typical procedure, the spent reactor fuel (e.g. MOX fuel) is dissolved in nitric acid, and the bulk of uranium and plutonium is removed using a PUREX-type extraction (Plutonium–URanium EXtraction) with tributyl phosphate in a hydrocarbon. The lanthanides and remaining actinides are then...	{ "page_id": 900, "source": null, "title": "Americium" }
\mathrm {3\ AmO_{2}\ +\ 4\ La\ \longrightarrow \ 3\ Am\ +\ 2\ La_{2}O_{3}} } == Physical properties == In the periodic table, americium is located to the right of plutonium, to the left of curium, and below the lanthanide europium, with which it shares many physical and chemical properties. Americium is a highly radioa...	{ "page_id": 900, "source": null, "title": "Americium" }
to 52 GPa, except for an appearance of a monoclinic phase at pressures between 10 and 15 GPa. There is no consistency on the status of this phase in the literature, which also sometimes lists the α, β and γ phases as I, II and III. The β-γ transition is accompanied by a 6% decrease in the crystal volume; although theor...	{ "page_id": 900, "source": null, "title": "Americium" }
show a rapid rise up to 60 K followed by saturation. The room temperature value for americium is lower than that of neptunium, plutonium and curium, but higher than for uranium, thorium and protactinium. Americium is paramagnetic in a wide temperature range, from that of liquid helium, to room temperature and above. Th...	{ "page_id": 900, "source": null, "title": "Americium" }
(MnO−4) in acidic solutions. Whereas the Am4+ ions are unstable in solutions and readily convert to Am3+, compounds such as americium dioxide (AmO2) and americium(IV) fluoride (AmF4) are stable in the solid state. The pentavalent oxidation state of americium was first observed in 1951. In acidic aqueous solution the Am...	{ "page_id": 900, "source": null, "title": "Americium" }
solutions. Reduction of Am(III) compounds with sodium amalgam yields Am(II) salts – the black halides AmCl2, AmBr2 and AmI2. They are very sensitive to oxygen and oxidize in water, releasing hydrogen and converting back to the Am(III) state. Specific lattice constants are: Orthorhombic AmCl2: a = 896.3±0.8 pm, b = 757....	{ "page_id": 900, "source": null, "title": "Americium" }
reddish and has a structure isotypic to uranium(III) chloride (space group P63/m) and the melting point of 715 °C. The fluoride is isotypic to LaF3 (space group P63/mmc) and the iodide to BiI3 (space group R3). The bromide is an exception with the orthorhombic PuBr3-type structure and space group Cmcm. Crystals of amer...	{ "page_id": 900, "source": null, "title": "Americium" }
complex is also known that is likely to be stoichiometrically AmCp3. Formation of the complexes of the type Am(n-C3H7-BTP)3, where BTP stands for 2,6-di(1,2,4-triazin-3-yl)pyridine, in solutions containing n-C3H7-BTP and Am3+ ions has been confirmed by EXAFS. Some of these BTP-type complexes selectively interact with a...	{ "page_id": 900, "source": null, "title": "Americium" }
reactors. There are proposals of very compact 10-kW high-flux reactors using as little as 20 grams of 242mAm. Such low-power reactors would be relatively safe to use as neutron sources for radiation therapy in hospitals. == Isotopes == About 18 isotopes and 11 nuclear isomers are known for americium, having mass number...	{ "page_id": 900, "source": null, "title": "Americium" }
241Am in the form of americium dioxide as its source of ionizing radiation. This isotope is preferred over 226Ra because it emits 5 times more alpha particles and relatively little harmful gamma radiation. The amount of americium in a typical new smoke detector is 1 microcurie (37 kBq) or 0.29 microgram. This amount de...	{ "page_id": 900, "source": null, "title": "Americium" }
problem of self-absorption of emitted radiation. This problem is pertinent to uranium or plutonium rods, in which only surface layers provide alpha-particles. The fission products of 242mAm can either directly propel the spaceship or they can heat a thrusting gas. They can also transfer their energy to a fluid and gene...	{ "page_id": 900, "source": null, "title": "Americium" }
device used to measure the quantity of water present in soil, as well as moisture/density for quality control in highway construction. 241Am neutron sources are also used in well logging applications, as well as in neutron radiography, tomography and other radiochemical investigations. === Production of other elements ...	{ "page_id": 900, "source": null, "title": "Americium" }
to help create flat glass. Americium-241 is also suitable for calibration of gamma-ray spectrometers in the low-energy range, since its spectrum consists of nearly a single peak and negligible Compton continuum (at least three orders of magnitude lower intensity). Americium-241 gamma rays were also used to provide pass...	{ "page_id": 900, "source": null, "title": "Americium" }
was exposed to 500 times the occupational standard for americium-241 as a result of an explosion in his lab. McCluskey died at the age of 75 of unrelated pre-existing disease. == See also == Actinides in the environment Category:Americium compounds == Notes == == References == == Bibliography == Greenwood, Norman N.; E...	{ "page_id": 900, "source": null, "title": "Americium" }
In molecular biology mir-202 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. The pre-miR-202 in the mouse genome is located fully within an exon, whereas in human it lies across a splice junction. This implies that human miR-202 is exposed to ...	{ "page_id": 36373382, "source": null, "title": "Mir-202 microRNA precursor family" }
Astatine is a chemical element; it has symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. Consequen...	{ "page_id": 901, "source": null, "title": "Astatine" }
Most of its isotopes are very unstable, with half-lives of seconds or less. Of the first 101 elements in the periodic table, only francium is less stable, and all the astatine isotopes more stable than the longest-lived francium isotopes (205–211At) are in any case synthetic and do not occur in nature. The bulk propert...	{ "page_id": 901, "source": null, "title": "Astatine" }
of 0.7 eV). Alternatively, if condensed astatine forms a metallic phase, as has been predicted, it may have a monatomic face-centered cubic structure; in this structure, it may well be a superconductor, like the similar high-pressure phase of iodine. Metallic astatine is expected to have a density of 8.91–8.95 g/cm3. E...	{ "page_id": 901, "source": null, "title": "Astatine" }
revised Pauling scale – lower than that of iodine (2.66) and the same as hydrogen. In hydrogen astatide (HAt), the negative charge is predicted to be on the hydrogen atom, implying that this compound could be referred to as astatine hydride according to certain nomenclatures. That would be consistent with the electrone...	{ "page_id": 901, "source": null, "title": "Astatine" }
adopt odd-numbered oxidation states ranging from −1 to +7. Only a few compounds with metals have been reported, in the form of astatides of sodium, palladium, silver, thallium, and lead. Some characteristic properties of silver and sodium astatide, and the other hypothetical alkali and alkaline earth astatides, have be...	{ "page_id": 901, "source": null, "title": "Astatine" }
product of AtO+ (another such hydrolysis product being AtOOH). The well characterized AtO−3 anion can be obtained by, for example, the oxidation of astatine with potassium hypochlorite in a solution of potassium hydroxide. Preparation of lanthanum triastatate La(AtO3)3, following the oxidation of astatine by a hot Na2S...	{ "page_id": 901, "source": null, "title": "Astatine" }
to have been precipitated. In a plasma ion source mass spectrometer, the ions [AtI]+, [AtBr]+, and [AtCl]+ have been formed by introducing lighter halogen vapors into a helium-filled cell containing astatine, supporting the existence of stable neutral molecules in the plasma ion state. No astatine fluorides have been d...	{ "page_id": 901, "source": null, "title": "Astatine" }
isolated as the thorium series equivalent of radium F (polonium-210) in the radium series. The properties he reported for dakin do not correspond to those of astatine, and astatine's radioactivity would have prevented him from handling it in the quantities he claimed. Moreover, astatine is not found in the thorium seri...	{ "page_id": 901, "source": null, "title": "Astatine" }
Bernert were unsuccessful in reproducing his experiments, and subsequently attributed Minder's results to contamination of his radon stream (radon-222 is the parent isotope of polonium-218). In 1942, Minder, in collaboration with the English scientist Alice Leigh-Smith, announced the discovery of another isotope of ele...	{ "page_id": 901, "source": null, "title": "Astatine" }
"-ine", found in the names of the four previously discovered halogens. The name was also chosen to continue the tradition of the four stable halogens, where the name referred to a property of the element. Corson and his colleagues classified astatine as a metal on the basis of its analytical chemistry. Subsequent inves...	{ "page_id": 901, "source": null, "title": "Astatine" }
that 215At is in fact beta-stable, as it has the lowest mass of all isobars with A = 215. Astatine-210 and most of the lighter isotopes exhibit beta plus decay (positron emission), astatine-217 and heavier isotopes except astatine-218 exhibit beta minus decay, while astatine-211 undergoes electron capture. The most sta...	{ "page_id": 901, "source": null, "title": "Astatine" }
Any astatine present at the formation of the Earth has long since disappeared; the four naturally occurring isotopes (astatine-215, -217, -218 and -219) are instead continuously produced as a result of the decay of radioactive thorium and uranium ores, and trace quantities of neptunium-237. The landmass of North and So...	{ "page_id": 901, "source": null, "title": "Astatine" }
generated via proton irradiation of thorium or uranium to yield radon-211, in turn decaying to astatine-211. Contamination with astatine-210 is expected to be a drawback of this method. The most important isotope is astatine-211, the only one in commercial use. To produce the bismuth target, the metal is sputtered onto...	{ "page_id": 901, "source": null, "title": "Astatine" }
650 °C. The astatine volatilizes and is condensed in (typically) a cold trap. Higher temperatures of up to around 850 °C may increase the yield, at the risk of bismuth contamination from concurrent volatilization. Redistilling the condensate may be required to minimize the presence of bismuth (as bismuth can interfere ...	{ "page_id": 901, "source": null, "title": "Astatine" }
and may have greater applicability in experimental radiochemistry. == Uses and precautions == Newly formed astatine-211 is the subject of ongoing research in nuclear medicine. It must be used quickly as it decays with a half-life of 7.2 hours; this is long enough to permit multistep labeling strategies. Astatine-211 ha...	{ "page_id": 901, "source": null, "title": "Astatine" }
indicated that a cancer-selective carrier would need to be developed and it was not until the 1970s that monoclonal antibodies became available for this purpose. Unlike iodine, astatine shows a tendency to dehalogenate from molecular carriers such as these, particularly at sp3 carbon sites (less so from sp2 sites). Giv...	{ "page_id": 901, "source": null, "title": "Astatine" }
irradiation of the ovaries. Trace amounts of astatine can be handled safely in fume hoods if they are well-aerated; biological uptake of the element must be avoided. == See also == Radiation protection == Notes == == References == == Bibliography == Corson, D. R.; MacKenzie, K. R.; Segrè, E. (1940). "Artificially Radio...	{ "page_id": 901, "source": null, "title": "Astatine" }
In biology, trimorphism is the existence in certain plants and animals of three distinct forms, especially in connection with the reproductive organs. In trimorphic plants there are three forms, differing in the lengths of their pistils and stamens, in size and color of their pollen grains, and in some other respects; ...	{ "page_id": 1377160, "source": null, "title": "Trimorphism" }
Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that con...	{ "page_id": 902, "source": null, "title": "Atom" }
protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements. This is a form of nuclear decay. Atoms can attach to one or more other atoms by chemical bonds to form chemical compo...	{ "page_id": 902, "source": null, "title": "Atom" }
grey powder that is 88.1% tin and 11.9% oxygen, and the other is a white powder that is 78.7% tin and 21.3% oxygen. Adjusting these figures, in the grey powder there is about 13.5 g of oxygen for every 100 g of tin, and in the white powder there is about 27 g of oxygen for every 100 g of tin. 13.5 and 27 form a ratio o...	{ "page_id": 902, "source": null, "title": "Atom" }
70.5% oxygen. Adjusting these figures, in nitrous oxide there is 80 g of oxygen for every 140 g of nitrogen, in nitric oxide there is about 160 g of oxygen for every 140 g of nitrogen, and in nitrogen dioxide there is 320 g of oxygen for every 140 g of nitrogen. 80, 160, and 320 form a ratio of 1:2:4. The respective fo...	{ "page_id": 902, "source": null, "title": "Atom" }
atom, the atom being in the shape of a sphere. This was the mathematically simplest hypothesis to fit the available evidence, or lack thereof. Following from this, Thomson imagined that the balance of electrostatic forces would distribute the electrons throughout the sphere in a more or less even manner. Thomson's mode...	{ "page_id": 902, "source": null, "title": "Atom" }
down into that nucleus as it loses speed. In 1913, the physicist Niels Bohr proposed a new model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in a finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radia...	{ "page_id": 902, "source": null, "title": "Atom" }
number") was found to be equal to the element's ordinal number on the periodic table and therefore provided a simple and clear-cut way of distinguishing the elements from each other. The atomic weight of each element is higher than its proton number, so Rutherford hypothesized that the surplus weight was carried by unk...	{ "page_id": 902, "source": null, "title": "Atom" }
for both the position and momentum of a particle at a given point in time. This became known as the uncertainty principle, formulated by Werner Heisenberg in 1927. In this concept, for a given accuracy in measuring a position one could only obtain a range of probable values for momentum, and vice versa. Thus, the plane...	{ "page_id": 902, "source": null, "title": "Atom" }
called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that the hydrogen nucleus is a distinct particle within the atom and named it proton. Neutrons have no electrical charge and have a mass of 1.674...	{ "page_id": 902, "source": null, "title": "Atom" }
equal to 1.07 A 3 {\displaystyle 1.07{\sqrt[{3}]{A}}} femtometres, where A {\displaystyle A} is the total number of nucleons. This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are bound together by a short-ranged attractive potential called the residual strong force. At dis...	{ "page_id": 902, "source": null, "title": "Atom" }
energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the Sun protons require energies of 3 to 10 keV to overcome their mutual repulsion—the coulomb barrier—and fuse to...	{ "page_id": 902, "source": null, "title": "Atom" }
about 26, and a mass number higher than about 60, is an endothermic process. Thus, more massive nuclei cannot undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star. === Electron cloud === The electrons in an atom are attracted to the protons in the nucleus by the electromagn...	{ "page_id": 902, "source": null, "title": "Atom" }
energy values, defined by the differences in the energies of the quantum states, are responsible for atomic spectral lines. The amount of energy needed to remove or add an electron—the electron binding energy—is far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state ...	{ "page_id": 902, "source": null, "title": "Atom" }
the total to 251) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 35 radioactive nuclides have half-lives longer than 100 million years, and are long-lived enough to have been present since the birth of the Solar System. ...	{ "page_id": 902, "source": null, "title": "Atom" }
a billion years: potassium-40, vanadium-50, lanthanum-138, and lutetium-176. Most odd-odd nuclei are highly unstable with respect to beta decay, because the decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects. === Mass === The large majority of an atom's mass comes from t...	{ "page_id": 902, "source": null, "title": "Atom" }
mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 Da, and so a mole of carbon-12 atoms weighs exactly 0.012 kg. === Shape and size === Atoms lack a well-defined outer boundary, so their dimensions a...	{ "page_id": 902, "source": null, "title": "Atom" }
an optical microscope, although individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width. A single drop of water contains about 2 sextillion (2×1021) atoms of oxygen, and twice the number ...	{ "page_id": 902, "source": null, "title": "Atom" }
emission, because it requires less energy. In this type of decay, an electron is absorbed by the nucleus, rather than a positron emitted from the nucleus. A neutrino is still emitted in this process, and a proton changes to a neutron. Gamma decay: this process results from a change in the energy level of the nucleus to...	{ "page_id": 902, "source": null, "title": "Atom" }
is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin 1⁄2 ħ, or "spin-1⁄2". In an atom, electrons in motion around the nucleus possess orbital angular momentum in addition to their spin, while the nucleus itself possesses angular momentum due to its nuclear spin. ...	{ "page_id": 902, "source": null, "title": "Atom" }
the nucleus may have a spin. Normally nuclei with spin are aligned in random directions because of thermal equilibrium, but for certain elements (such as xenon-129) it is possible to polarize a significant proportion of the nuclear spin states so that they are aligned in the same direction—a condition called hyperpolar...	{ "page_id": 902, "source": null, "title": "Atom" }
only a single electron changes states in response to the photon; see Electron properties. The energy of an emitted photon is proportional to its frequency, so these specific energy levels appear as distinct bands in the electromagnetic spectrum. Each element has a characteristic spectrum that can depend on the nuclear ...	{ "page_id": 902, "source": null, "title": "Atom" }
atom shifts these electron configurations to slightly different energy levels, resulting in multiple spectral lines. The presence of an external electric field can cause a comparable splitting and shifting of spectral lines by modifying the electron energy levels, a phenomenon called the Stark effect. If a bound electr...	{ "page_id": 902, "source": null, "title": "Atom" }
Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds. The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and ele...	{ "page_id": 902, "source": null, "title": "Atom" }
exponentially dependent on their separation. One electrode is a sharp tip ideally ending with a single atom. At each point of the scan of the surface the tip's height is adjusted so as to keep the tunneling current at a set value. How much the tip moves to and away from the surface is interpreted as the height profile....	{ "page_id": 902, "source": null, "title": "Atom" }
in a non-destructive way. With proper focusing both can be made area-specific. Another such method is electron energy loss spectroscopy (EELS), which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample. Spectra of excited states can be used...	{ "page_id": 902, "source": null, "title": "Atom" }
make electron shells impossible. === Formation === Electrons are thought to exist in the Universe since early stages of the Big Bang. Atomic nuclei forms in nucleosynthesis reactions. In about three minutes Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the Universe, and perhaps some of...	{ "page_id": 902, "source": null, "title": "Atom" }
and its inhabitants were present in their current form in the nebula that collapsed out of a molecular cloud to form the Solar System. The rest are the result of radioactive decay, and their relative proportion can be used to determine the age of the Earth through radiometric dating. Most of the helium in the crust of ...	{ "page_id": 902, "source": null, "title": "Atom" }
with molecular matter. === Rare and theoretical forms === ==== Superheavy elements ==== All nuclides with atomic numbers higher than 82 (lead) are known to be radioactive. No nuclide with an atomic number exceeding 92 (uranium) exists on Earth as a primordial nuclide, and heavier elements generally have shorter half-li...	{ "page_id": 902, "source": null, "title": "Atom" }
Notes == == References == == Bibliography == Oliver Manuel (2001). Origin of Elements in the Solar System: Implications of Post-1957 Observations. Springer. ISBN 978-0-306-46562-8. OCLC 228374906. Andrew G. van Melsen (2004) [1952]. From Atomos to Atom: The History of the Concept Atom. Translated by Henry J. Koren. Dov...	{ "page_id": 902, "source": null, "title": "Atom" }
A Bland–Altman plot (difference plot) in analytical chemistry or biomedicine is a method of data plotting used in analyzing the agreement between two different assays. It is identical to a Tukey mean-difference plot, the name by which it is known in other fields, but was popularised in medical statistics by J. Martin B...	{ "page_id": 3146632, "source": null, "title": "Bland–Altman plot" }
== Interpretation of a Bland-Altman plot is contingent on the construction of the plot and data at hand. Variations to the default plot have introduced throughout the years and each should be interpreted accordingly. === Original Construction === The original plot displays a scatter plot of differences between individu...	{ "page_id": 3146632, "source": null, "title": "Bland–Altman plot" }
and the contexts in which they are to be used. The 95% limits of agreement can be unreliable estimates of the population parameters especially for small sample sizes so, when comparing methods or assessing repeatability, it is important to calculate confidence intervals for 95% limits of agreement. This can be done by ...	{ "page_id": 3146632, "source": null, "title": "Bland–Altman plot" }
be used to compare a new reference system, technique, or method with a verified gold standard, but a gold standard does not imply it to be without error. In order for the plot to be used to verify a reference system, a threshold is typically predetermined for which the limits of agreement must fall under. The value for...	{ "page_id": 3146632, "source": null, "title": "Bland–Altman plot" }
Aluminium (or aluminum in North American English) is a chemical element; it has symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has a great affinity towards oxygen, forming a protective layer of oxide on the surface when exposed to air. I...	{ "page_id": 904, "source": null, "title": "Aluminium" }
First and Second World Wars, aluminium was a crucial strategic resource for aviation. In 1954, aluminium became the most produced non-ferrous metal, surpassing copper. In the 21st century, most aluminium was consumed in transportation, engineering, construction, and packaging in the United States, Western Europe, and J...	{ "page_id": 904, "source": null, "title": "Aluminium" }
transport, deposition, sediment storage, burial times, and erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago. The remaining isotopes of aluminium, with mass numbers r...	{ "page_id": 904, "source": null, "title": "Aluminium" }
close-packed like those of aluminium and thallium. The few electrons that are available for metallic bonding in aluminium are a probable cause for it being soft with a low melting point and low electrical resistivity. === Bulk === Aluminium metal has an appearance ranging from silvery white to dull gray depending on it...	{ "page_id": 904, "source": null, "title": "Aluminium" }
drawn and extruded. It is also easily machined and cast. Aluminium is an excellent thermal and electrical conductor, having around 60% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperatur...	{ "page_id": 904, "source": null, "title": "Aluminium" }
icosahedral structures, and aluminium forms an important part of many icosahedral quasicrystal alloys, including the Al–Zn–Mg class. Aluminium has a high chemical affinity to oxygen, which renders it suitable for use as a reducing agent in the thermite reaction. A fine powder of aluminium reacts explosively on contact ...	{ "page_id": 904, "source": null, "title": "Aluminium" }
all compounds of aluminium(III) are colorless. In aqueous solution, Al3+ exists as the hexaaqua cation [Al(H2O)6]3+, which has an approximate Ka of 10−5. Such solutions are acidic as this cation can act as a proton donor and progressively hydrolyze until a precipitate of aluminium hydroxide, Al(OH)3, forms. This is use...	{ "page_id": 904, "source": null, "title": "Aluminium" }
with each fluorine atom being shared between the corners of two octahedra. Such {AlF6} units also exist in complex fluorides such as cryolite, Na3AlF6. AlF3 melts at 1,290 °C (2,354 °F) and is made by reaction of aluminium oxide with hydrogen fluoride gas at 700 °C (1,300 °F). With heavier halides, the coordination num...	{ "page_id": 904, "source": null, "title": "Aluminium" }
production of aluminium. Sapphire and ruby are impure corundum contaminated with trace amounts of other metals. The two main oxide-hydroxides, AlO(OH), are boehmite and diaspore. There are three main trihydroxides: bayerite, gibbsite, and nordstrandite, which differ in their crystalline structure (polymorphs). Many oth...	{ "page_id": 904, "source": null, "title": "Aluminium" }
alkali metals and group 13 metals) and over 150 intermetallics with other metals are known. Preparation involves heating fixed metals together in certain proportion, followed by gradual cooling and annealing. Bonding in them is predominantly metallic and the crystal structure primarily depends on efficiency of packing....	{ "page_id": 904, "source": null, "title": "Aluminium" }
alkenes and alcohols, and in the low-pressure polymerization of ethene and propene. There are also some heterocyclic and cluster organoaluminium compounds involving Al–N bonds. The industrially most important aluminium hydride is lithium aluminium hydride (LiAlH4), which is used as a reducing agent in organic chemistry...	{ "page_id": 904, "source": null, "title": "Aluminium" }
Milky Way would be brighter. === Earth === Overall, the Earth is about 1.59% aluminium by mass (seventh in abundance by mass). Aluminium occurs in greater proportion in the Earth's crust than in the universe at large. This is because aluminium easily forms the oxide and becomes bound into rocks and stays in the Earth's...	{ "page_id": 904, "source": null, "title": "Aluminium" }
Guinea, and India. == History == The history of aluminium has been shaped by usage of alum. The first written record of alum, made by Greek historian Herodotus, dates back to the 5th century BCE. The ancients are known to have used alum as a dyeing mordant and for city defense. After the Crusades, alum, an indispensabl...	{ "page_id": 904, "source": null, "title": "Aluminium" }
metal remained rare; its cost exceeded that of gold. The first industrial production of aluminium was established in 1856 by French chemist Henri Etienne Sainte-Claire Deville and companions. Deville had discovered that aluminium trichloride could be reduced by sodium, which was more convenient and less expensive than ...	{ "page_id": 904, "source": null, "title": "Aluminium" }

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.