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History of atomic theory
Atoms in philosophyThe idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India. The word atomos, meaning "uncuttable", was coined by the ancient Greek philosophers Leucippus and his pupil Democritus ({{circa}} 460 â {{circa}} 370 BC).BOOK, Pullman, Bernard, The Atom in the History of Human Thought, 1998, Oxford University Press, Oxford, England, 978-0-19-515040-7, 31â33,weblink harv, BOOK, Kenny, Anthony, Anthony Kenny, 2004, Ancient Philosophy,weblink A New History of Western Philosophy, 1, Oxford, England, Oxford University Press, 978-0-19-875273-8, 26â28, harv, BOOK, Pyle, Andrew, Andrew Pyle (philosopher), 2010, Atoms and Atomism, The Classical Tradition,weblink Grafton, Anthony, Anthony Grafton, Most, Glenn W., Glenn W. Most, Settis, Salvatore, The Belknap Press of Harvard University Press, Cambridge, Massachusetts and London, 978-0-674-03572-0, 103â104, harv, BOOK, Cohen, Henri, Lefebvre, Claire, Handbook of Categorization in Cognitive Science, 2017, Elsevier, Amsterdam, The Netherlands, 978-0-08-101107-2, 427, Second,weblink harv, Democritus taught that atoms were infinite in number, uncreated, and eternal, and that the qualities of an object result from the kind of atoms that compose it. Democritus's atomism was refined and elaborated by the later philosopher Epicurus (341â270 BC). During the Early Middle Ages, atomism was mostly forgotten in western Europe, but survived among some groups of Islamic philosophers. During the twelfth century, atomism became known again in western Europe through references to it in the newly-rediscovered writings of Aristotle.In the fourteenth century, the rediscovery of major works describing atomist teachings, including Lucretius's De rerum natura and Diogenes Laërtius's Lives and Opinions of Eminent Philosophers, led to increased scholarly attention on the subject. Nonetheless, because atomism was associated with the philosophy of Epicureanism, which contradicted orthodox Christian teachings, belief in atoms was not considered acceptable. The French Catholic priest Pierre Gassendi (1592â1655) revived Epicurean atomism with modifications, arguing that atoms were created by God and, though extremely numerous, are not infinite. Gassendi's modified theory of atoms was popularized in France by the physician François Bernier (1620â1688) and in England by the natural philosopher Walter Charleton (1619â1707). The chemist Robert Boyle (1627â1691) and the physicist Isaac Newton (1642â1727) both defended atomism and, by the end of the seventeenth century, it had become accepted by portions of the scientific community.
First evidence-based theoryFile:Daltons symbols.gif|right|thumb|Various atoms and molecules as depicted in John DaltonJohn DaltonIn the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers (the law of multiple proportions). For instance, there are two types of tin oxide: one is 88.1% tin and 11.9% oxygen and the other is 78.7% tin and 21.3% oxygen (tin(II) oxide and tin dioxide respectively). This means that 100g of tin will combine either with 13.5g or 27g of oxygen. 13.5 and 27 form a ratio of 1:2, a ratio of small whole numbers. This common pattern in chemistry suggested to Dalton that elements react in multiples of discrete units â in other words, atoms. In the case of tin oxides, one tin atom will combine with either one or two oxygen atoms.BOOK, Andrew G. van Melsen, 1952, From Atomos to Atom, 978-0-486-49584-2, Dover Publications, Mineola, NY, Dalton also believed atomic theory could explain why water absorbs different gases in different proportions. For example, he found that water absorbs carbon dioxide far better than it absorbs nitrogen.Dalton, John. "On the Absorption of Gases by Water and Other Liquids {{Webarchive|url=https://web.archive.org/web/20110611205519weblink |date=11 June 2011 }}", in Memoirs of the Literary and Philosophical Society of Manchester. 1803. Retrieved on August 29, 2007. Dalton hypothesized this was due to the differences between the masses and configurations of the gases' respective particles, and carbon dioxide molecules (CO2) are heavier and larger than nitrogen molecules (N2).
Brownian motionIn 1827, botanist Robert Brown used a microscope to look at dust grains floating in water and discovered that they moved about erratically, a phenomenon that became known as "Brownian motion". This was thought to be caused by water molecules knocking the grains about. In 1905, Albert Einstein proved the reality of these molecules and their motions by producing the first statistical physics analysis of Brownian motion."MEMBERWIDE">
French physicist Jean Perrin used Einstein's work to experimentally determine the mass and dimensions of atoms, thereby conclusively verifying Dalton's atomic theory.
Discovery of the electronFile:Geiger-Marsden experiment expectation and result.svg|thumb|right|The (GeigerâMarsden experiment]] Left: Expected results: alpha particles passing through the plum pudding model of the atom with negligible deflection. Right: Observed results: a small portion of the particles were deflected by the concentrated positive charge of the nucleus.)The physicist J.J. Thomson measured the mass of cathode rays, showing they were made of particles, but were around 1800 times lighter than the lightest atom, hydrogen. Therefore, they were not atoms, but a new particle, the first subatomic particle to be discovered, which he originally called "(wikt:corpuscle|corpuscle)" but was later named electron, after particles postulated by George Johnstone Stoney in 1874. He also showed they were identical to particles given off by photoelectric and radioactive materials.JOURNAL, Thomson, J.J., On bodies smaller than atoms, The Popular Science Monthly, 323â335, August 1901,weblink 2009-06-21, It was quickly recognized that they are the particles that carry electric currents in metal wires, and carry the negative electric charge within atoms. Thomson was given the 1906 Nobel Prize in Physics for this work. Thus he overturned the belief that atoms are the indivisible, ultimate particles of matter. Thomson also incorrectly postulated that the low mass, negatively charged electrons were distributed throughout the atom in a uniform sea of positive charge. This became known as the plum pudding model.
Discovery of the nucleusIn 1909, Hans Geiger and Ernest Marsden, under the direction of Ernest Rutherford, bombarded a metal foil with alpha particles to observe how they scattered. They expected all the alpha particles to pass straight through with little deflection, because Thomson's model said that the charges in the atom are so diffuse that their electric fields could not affect the alpha particles much. However, Geiger and Marsden spotted alpha particles being deflected by angles greater than 90°, which was supposed to be impossible according to Thomson's model. To explain this, Rutherford proposed that the positive charge of the atom is concentrated in a tiny nucleus at the center of the atom.
Discovery of isotopesWhile experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table. The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J.J. Thomson created a technique for isotope separation through his work on ionized gases, which subsequently led to the discovery of stable isotopes.
Bohr model(File:Bohr atom animation 2.gif|right|thumb|The Bohr model of the atom, with an electron making instantaneous "quantum leaps" from one orbit to another. This model is obsolete.)In 1913 the physicist Niels Bohr proposed a 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 radiation of a photon. This quantization was used to explain why the electrons orbits are stable (given that normally, charges in acceleration, including circular motion, lose kinetic energy which is emitted as electromagnetic radiation, see synchrotron radiation) and why elements absorb and emit electromagnetic radiation in discrete spectra.Later in the same year Henry Moseley provided additional experimental evidence in favor of Niels Bohr's theory. These results refined Ernest Rutherford's and Antonius Van den Broek's model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today.BOOK, Pais, Abraham, 1986, New York, Inward Bound: Of Matter and Forces in the Physical World, Oxford University Press, 978-0-19-851971-3, 228â230,weblink
Chemical bonding explainedChemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons. As the chemical properties of the elements were known to largely repeat themselves according to the periodic law,SCERRI>FIRST=ERIC R., The periodic table: its story and its significance
Further developments in quantum physicsThe SternâGerlach experiment of 1922 provided further evidence of the quantum nature of atomic properties. When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split in a way correlated with the direction of an atom's angular momentum, or spin. As this spin direction is initially random, the beam would be expected to deflect in a random direction. Instead, the beam was split into two directional components, corresponding to the atomic spin being oriented up or down with respect to the magnetic field.In 1925 Werner Heisenberg published the first consistent mathematical formulation of quantum mechanics (Matrix Mechanics). One year earlier, in 1924, Louis de Broglie had proposed that all particles behave to an extent like waves and, in 1926, Erwin Schrödinger used this idea to develop a mathematical model of the atom (Wave Mechanics) that described the electrons as three-dimensional waveforms rather than point particles.A consequence of using waveforms to describe particles is that it is mathematically impossible to obtain precise values 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.WEB, Chad Orzel,weblink What is the Heisenberg Uncertainty Principle?, TED-Ed, 16 September 2014, YouTube, 26 October 2015,weblink 13 September 2015, live, This model was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen. Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be observed.
Discovery of the neutronThe development of the mass spectrometer allowed the mass of atoms to be measured with increased accuracy. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom's mass to its charge. The chemist Francis William Aston used this instrument to show that isotopes had different masses. The atomic mass of these isotopes varied by integer amounts, called the whole number rule. The explanation for these different isotopes awaited the discovery of the neutron, an uncharged particle with a mass similar to the proton, by the physicist James Chadwick in 1932. Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.
Fission, high-energy physics and condensed matterIn 1938, the German chemist Otto Hahn, a student of Rutherford, directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product. A year later, Lise Meitner and her nephew Otto Frisch verified that Hahn's result were the first experimental nuclear fission. In 1944, Hahn received the Nobel prize in chemistry. Despite Hahn's efforts, the contributions of Meitner and Frisch were not recognized.In the 1950s, the development of improved particle accelerators and particle detectors allowed scientists to study the impacts of atoms moving at high energies. Neutrons and protons were found to be hadrons, or composites of smaller particles called quarks. The standard model of particle physics was developed that so far has successfully explained the properties of the nucleus in terms of these sub-atomic particles and the forces that govern their interactions.
Subatomic particlesThough the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron; all three are fermions. However, the hydrogen-1 atom has no neutrons and the hydron ion has no electrons.The electron is by far the least massive of these particles at {{val|9.11|e=-31|u=kg}}, with a negative electrical charge and a size that is too small to be measured using available techniques.BOOK, Demtröder, Wolfgang, 2002, Atoms, Molecules and Photons: An Introduction to Atomic- Molecular- and Quantum Physics, Springer, 1st, 978-3-540-20631-6, 181435713, 39â42, It was the lightest particle with a positive rest mass measured, until the discovery of neutrino mass. Under ordinary conditions, electrons are bound to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson; see history of subatomic physics for details.Protons have a positive charge and a mass 1,836 times that of the electron, at {{val|1.6726|e=-27|u=kg}}. The number of protons in an atom is 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 free mass of 1,839 times the mass of the electron, or {{val|1.6749|e=-27|u=kg}}.BOOK, Woan, Graham, 2000, The Cambridge Handbook of Physics, Cambridge University Press, 978-0-521-57507-2, 224032426, 8, Mohr, P.J.; Taylor, B.N. and Newell, D.B. (2014), "The 2014 CODATA Recommended Values of the Fundamental Physical Constants" {{Webarchive|url=https://www.webcitation.org/65cjrPoqR?url=http://physics.nist.gov/cuu/Constants/index.html |date=21 February 2012 }} (Web Version 7.0). The database was developed by J. Baker, M. Douma, and S. Kotochigova. (2014). National Institute of Standards and Technology, Gaithersburg, Maryland 20899. Neutrons are the heaviest of the three constituent particles, but their mass can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensionsâon the order of {{val|2.5|e=-15|u=m}}âalthough the 'surface' of these particles is not sharply defined.BOOK, MacGregor, Malcolm H., 1992, The Enigmatic Electron, Oxford University Press, 978-0-19-521833-6, 223372888, 33â37,weblink The neutron was discovered in 1932 by the English physicist James Chadwick.In the Standard Model of physics, electrons are truly elementary particles with no internal structure. However, both protons and neutrons are composite particles composed of elementary particles called quarks. There are two types of quarks in atoms, each having a fractional electric charge. Protons are composed of two up quarks (each with charge +{{sfrac|2|3}}) and one down quark (with a charge of â{{sfrac|1|3}}). Neutrons consist of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles.The quarks are held together by the strong interaction (or strong force), which is mediated by gluons. The protons and neutrons, in turn, are held to each other in the nucleus by the nuclear force, which is a residuum of the strong force that has somewhat different range-properties (see the article on the nuclear force for more). The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces.
NucleusFile:Binding energy curve - common isotopes.svg|thumb|The binding energybinding energyAll the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to 1.07 {{radic|A|3}} fm, where A is the total number of nucleons.BOOK, Jevremovic, Tatjana, 2005, Nuclear Principles in Engineering, Springer, 978-0-387-23284-3, 228384008, 63, 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 distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other.BOOK, Pfeffer, Jeremy I., Nir, Shlomo, 2000, Modern Physics: An Introductory Text, Imperial College Press, 978-1-86094-250-1, 45900880, 330â336, Atoms of the same element have the same number of protons, called the atomic number. Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine the nuclide. The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay.The proton, the electron, and the neutron are classified as fermions. Fermions obey the Pauli exclusion principle which prohibits identical fermions, such as multiple protons, from occupying the same quantum state at the same time. Thus, every proton in the nucleus must occupy a quantum state different from all other protons, and the same applies to all neutrons of the nucleus and to all electrons of the electron cloud.A nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with matching numbers of protons and neutrons are more stable against decay. However, with increasing atomic number, the mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus, which slightly modifies this trend of equal numbers of protons to neutrons.File:Wpdms physics proton proton chain 1.svg|right|thumb|upright|Illustration of a nuclear fusion process that forms a deuterium nucleus, consisting of a proton and a neutron, from two protons. A positron (e+)âan antimatter electronâis emitted along with an electron neutrinoneutrinoThe number of protons and neutrons in the atomic nucleus can be modified, although this can require very high 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 3â10 keV to overcome their mutual repulsionâthe coulomb barrierâand fuse together into a single nucleus. Nuclear fission is the opposite process, causing a nucleus to split into two smaller nucleiâusually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies the number of protons in a nucleus, the atom changes to a different chemical element.If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values can be emitted as a type of usable energy (such as a gamma ray, or the kinetic energy of a beta particle), as described by Albert Einstein's massâenergy equivalence formula, E=mc^2, where m is the mass loss and c is the speed of light. This deficit is part of the binding energy of the new nucleus, and it is the non-recoverable loss of the energy that causes the fused particles to remain together in a state that requires this energy to separate.BOOK, Shultis, J. Kenneth, Faw, Richard E., Fundamentals of Nuclear Science and Engineering, 2002, CRC Press, 978-0-8247-0834-4, 123346507, 10â17, The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickelâa total nucleon number of about 60âis usually an exothermic process that releases more energy than is required to bring them together. It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon in the nucleus begins to decrease. That means fusion processes producing nuclei that have atomic numbers higher than about 26, and atomic masses higher than about 60, is an endothermic process. These more massive nuclei can not undergo an energy-producing fusion reaction that can sustain the hydrostatic equilibrium of a star.
Electron cloudFile:Potential energy well.svg|right|thumb|A potential well, showing, according to classical mechanicsclassical mechanicsThe electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near the center of the potential well require more energy to escape than those at greater separations.Electrons, like other particles, have properties of both a particle and a wave. The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing waveâa wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital, a mathematical function that characterises the probability that an electron appears to be at a particular location when its position is measured. Only a discrete (or (wikt:quantize|quantized)) set of these orbitals exist around the nucleus, as other possible wave patterns rapidly decay into a more stable form. Orbitals can have one or more ring or node structures, and differ from each other in size, shape and orientation.File:Oganesson Subshells and Orbitals.tif|right|thumb| Oganesson. An illustration of all the Subshells/orbitals of the OganessonOganessonFile:S-p-Orbitals.svg|left|thumb|Wave functions of the first five atomic orbitals. The three 2p orbitals each display a single angular node that has an orientation and a minimum at the center.]](File:Atomic orbitals and periodic table construction.ogv|left|thumb|How atoms are constructed from electron orbitals and link to the periodic table.)Each atomic orbital corresponds to a particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission, an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic 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 electronâthe electron binding energyâis far less than the binding energy of nucleons. For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom, compared to 2.23 million eV for splitting a deuterium nucleus. Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals.BOOK, Smirnov, Boris M., 2003, Physics of Atoms and Ions, Springer, 978-0-387-95550-6, 249â272,
Nuclear propertiesBy definition, any two atoms with an identical number of protons in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form, also called protium), one neutron (deuterium), two neutrons (tritium) and more than two neutrons. The known elements form a set of atomic numbers, from the single proton element hydrogen up to the 118-proton element oganesson. All known isotopes of elements with atomic numbers greater than 82 are radioactive, although the radioactivity of element 83 (bismuth) is so slight as to be practically negligible.BOOK, Sills, Alan D., 2003, Earth Science the Easy Way, Barron's Educational Series, 978-0-7641-2146-3, 51543743, 131â134,weblink About 339 nuclides occur naturally on Earth, of which 254 (about 75%) have not been observed to decay, and are referred to as "stable isotopes". However, only 90 of these nuclides are stable to all decay, even in theory. Another 164 (bringing the total to 254) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 34 radioactive nuclides have half-lives longer than 80 million years, and are long-lived enough to be present from the birth of the solar system. This collection of 288 nuclides are known as primordial nuclides. Finally, an additional 51 short-lived nuclides are known to occur naturally, as daughter products of primordial nuclide decay (such as radium from uranium), or else as products of natural energetic processes on Earth, such as cosmic ray bombardment (for example, carbon-14).For more recent updates see Interactive Chart of Nuclides (Brookhaven National Laboratory) {{Webarchive|url=https://web.archive.org/web/20090825001001weblink |date=25 August 2009 }}.For 80 of the chemical elements, at least one stable isotope exists. As a rule, there is only a handful of stable isotopes for each of these elements, the average being 3.2 stable isotopes per element. Twenty-six elements have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten, for the element tin. Elements 43, 61, and all elements numbered 83 or higher have no stable isotopes.CRC Handbook (2002).{{Page needed|date=April 2011}}Stability of isotopes is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 254 known stable nuclides, only four have both an odd number of protons and odd number of neutrons: hydrogen-2 (deuterium), lithium-6, boron-10 and nitrogen-14. Also, only four naturally occurring, radioactive oddâodd nuclides have a half-life over a billion years: potassium-40, vanadium-50, lanthanum-138 and tantalum-180m. Most oddâodd nuclei are highly unstable with respect to beta decay, because the decay products are evenâeven, and are therefore more strongly bound, due to nuclear pairing effects.{{Page needed|date=April 2011}}
MassThe large majority of an atom's mass comes from the protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number. It is a positive integer and dimensionless (instead of having dimension of mass), because it expresses a count. An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons).The actual mass of an atom at rest is often expressed using the unified atomic mass unit (u), also called dalton (Da). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately {{val|1.66|e=-27|u=kg}}. Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 u. The value of this number is called the atomic mass. A given atom has an atomic mass approximately equal (within 1%) to its mass number times the atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 u). However, this number will not be exactly an integer except in the case of carbon-12 (see below). The heaviest stable atom is lead-208, with a mass of {{val|207.9766521|u=u}}.As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles. One mole of atoms of any element always has the same number of atoms (about {{val|6.022|e=23}}). This number was chosen so that if an element has an atomic mass of 1 u, a 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 u, and so a mole of carbon-12 atoms weighs exactly 0.012 kg.BOOK, Mills, Ian, Cvitaš, Tomislav, Homann, Klaus, Kallay, Nikola, Kuchitsu, Kozo, Quantities, Units and Symbols in Physical Chemistry, International Union of Pure and Applied Chemistry, Commission on Physiochemical Symbols Terminology and Units, Blackwell Scientific Publications, Oxford, 2nd, 1993, 978-0-632-03583-0, 27011505,weblink 70, 10 December 2011,weblink" title="web.archive.org/web/20111110141213weblink">weblink 10 November 2011, live,
Shape and sizeAtoms lack a well-defined outer boundary, so their dimensions are usually described in terms of an atomic radius. This is a measure of the distance out to which the electron cloud extends from the nucleus.JOURNAL, Ghosh, D.C., Biswas, R., Theoretical calculation of Absolute Radii of Atoms and Ions. Part 1. The Atomic Radii, Int. J. Mol. Sci., 3, 11, 87â113, 2002, 10.3390/i3020087, free, However, this assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Atomic radii may be derived from the distances between two nuclei when the two atoms are joined in a chemical bond. The radius varies with the location of an atom on the atomic chart, the type of chemical bond, the number of neighboring atoms (coordination number) and a quantum mechanical property known as spin. On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right). Consequently, the smallest atom is helium with a radius of 32 pm, while one of the largest is caesium at 225 pm.ZUMDAHL>FIRST=STEVEN S., 2002, Introductory Chemistry: A Foundation
Radioactive decayFile:Isotopes and half-life.svg|right|thumb|This diagram shows the half-lifehalf-lifeEvery element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing the nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm.The most common forms of radioactive decay are:BOOK, L'Annunziata, Michael F.
- Alpha decay: this process is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The result of the emission is a new element with a lower atomic number.
- Beta decay (and electron capture): these processes are regulated by the weak force, and result from a transformation of a neutron into a proton, or a proton into a neutron. The neutron to proton transition is accompanied by the emission of an electron and an antineutrino, while proton to neutron transition (except in electron capture) causes the emission of a positron and a neutrino. The electron or positron emissions are called beta particles. Beta decay either increases or decreases the atomic number of the nucleus by one. Electron capture is more common than positron 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 a lower state, resulting in the emission of electromagnetic radiation. The excited state of a nucleus which results in gamma emission usually occurs following the emission of an alpha or a beta particle. Thus, gamma decay usually follows alpha or beta decay.
Magnetic momentElementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of the reduced Planck constant (ħ), with electrons, protons and neutrons all having spin ½ ħ, or "spin-½". 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.The magnetic field produced by an atomâits magnetic momentâis determined by these various forms of angular momentum, just as a rotating charged object classically produces a magnetic field. However, the most dominant contribution comes from electron spin. Due to the nature of electrons to obey the Pauli exclusion principle, in which no two electrons may be found in the same quantum state, bound electrons pair up with each other, with one member of each pair in a spin up state and the other in the opposite, spin down state. Thus these spins cancel each other out, reducing the total magnetic dipole moment to zero in some atoms with even number of electrons.In ferromagnetic elements such as iron, cobalt and nickel, an odd number of electrons leads to an unpaired electron and a net overall magnetic moment. The orbitals of neighboring atoms overlap and a lower energy state is achieved when the spins of unpaired electrons are aligned with each other, a spontaneous process known as an exchange interaction. When the magnetic moments of ferromagnetic atoms are lined up, the material can produce a measurable macroscopic field. Paramagnetic materials have atoms with magnetic moments that line up in random directions when no magnetic field is present, but the magnetic moments of the individual atoms line up in the presence of a field.The nucleus of an atom will have no spin when it has even numbers of both neutrons and protons, but for other cases of odd numbers, the nucleus may have a spin. Normally nuclei with spin are aligned in random directions because of thermal equilibrium. However, 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 directionâa condition called hyperpolarization. This has important applications in magnetic resonance imaging.LIANG>FIRST1=Z.-P.
Energy levelsImage:Atomic orbital energy levels.svg|thumb|right|These electron's energy levels (not to scale) are sufficient for ground states of atoms up to cadmiumcadmiumThe potential energy of an electron in an atom is negative, its dependence of its position reaches the minimum (the most absolute value) inside the nucleus, and vanishes when the distance from the nucleus goes to infinity, roughly in an inverse proportion to the distance. In the quantum-mechanical model, a bound electron can only occupy a set of states centered on the nucleus, and each state corresponds to a specific energy level; see time-independent Schrödinger equation for theoretical explanation. An energy level can be measured by the amount of energy needed to unbind the electron from the atom, and is usually given in units of electronvolts (eV). The lowest energy state of a bound electron is called the ground state, i.e. stationary state, while an electron transition to a higher level results in an excited state. The electron's energy raises when n increases because the (average) distance to the nucleus increases. Dependence of the energy on {{ell}} is caused not by electrostatic potential of the nucleus, but by interaction between electrons.For an electron to transition between two different states, e.g. ground state to first excited state, it must absorb or emit a photon at an energy matching the difference in the potential energy of those levels, according to the Niels Bohr model, what can be precisely calculated by the Schrödinger equation.Electrons jump between orbitals in a particle-like fashion. For example, if a single photon strikes the electrons, 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.FOWLES>FIRST=GRANT R., 1989, Introduction to Modern Optics, Courier Dover Publications, 978-0-486-65957-2
Each element has a characteristic spectrum that can depend on the nuclear charge, subshells filled by electrons, the electromagnetic interactions between the electrons and other factors.(File:Fraunhofer lines.svg|right|thumb|upright=1.5|An example of absorption lines in a spectrum)When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom spontaneously emit this energy as a photon, traveling in a random direction, and so drop back to lower energy levels. Thus the atoms behave like a filter that forms a series of dark absorption bands in the energy output. (An observer viewing the atoms from a view that does not include the continuous spectrum in the background, instead sees a series of emission lines from the photons emitted by the atoms.) Spectroscopic measurements of the strength and width of atomic spectral lines allow the composition and physical properties of a substance to be determined.Close examination of the spectral lines reveals that some display a fine structure splitting. This occurs because of spinâorbit coupling, which is an interaction between the spin and motion of the outermost electron. When an atom is in an external magnetic field, spectral lines become split into three or more components; a phenomenon called the Zeeman effect. This is caused by the interaction of the magnetic field with the magnetic moment of the atom and its electrons. Some atoms can have multiple electron configurations with the same energy level, which thus appear as a single spectral line. The interaction of the magnetic field with the 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.BEYER>FIRST=H.F.
Valence and bonding behaviorValency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds.oxford dictionary â valency The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons inthat shell are called valence electrons. The number of valence electrons determines the bondingbehavior with other atoms. Atoms tend to chemically react with each other in a manner that fills (or empties) their outer valence shells. For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. 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 elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases.
StatesFile:Bose Einstein condensate.png|right|thumb|Graphic illustrating the formation of a BoseâEinstein condensateBoseâEinstein condensateQuantities of atoms are found in different states of matter that depend on the physical conditions, such as temperature and pressure. By varying the conditions, materials can transition between solids, liquids, gases and plasmas.GOODSTEIN>FIRST=DAVID L., 2002
IdentificationFile:Atomic resolution Au100.JPG|right|thumb|Scanning tunneling microscope image showing the individual atoms making up this gold (100) surface. The surface atoms deviate from the bulk crystal structure and arrange in columns several atoms wide with pits between them (See surface reconstructionsurface reconstructionThe scanning tunneling microscope is a device for viewing surfaces at the atomic level. It uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would normally be insurmountable. Electrons tunnel through the vacuum between two planar metal electrodes, on each of which is an adsorbed atom, providing a tunneling-current density that can be measured. Scanning one atom (taken as the tip) as it moves past the other (the sample) permits plotting of tip displacement versus lateral separation for a constant current. The calculation shows the extent to which scanning-tunneling-microscope images of an individual atom are visible. It confirms that for low bias, the microscope images the space-averaged dimensions of the electron orbitals across closely packed energy levelsâthe Fermi level local density of states.An atom can be ionized by removing one of its electrons. The electric charge causes the trajectory of an atom to bend when it passes through a magnetic field. The radius by which the trajectory of a moving ion is turned by the magnetic field is determined by the mass of the atom. The mass spectrometer uses this principle to measure the mass-to-charge ratio of ions. If a sample contains multiple isotopes, the mass spectrometer can determine the proportion of each isotope in the sample by measuring the intensity of the different beams of ions. Techniques to vaporize atoms include inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry, both of which use a plasma to vaporize samples for analysis.A more area-selective method is electron energy loss spectroscopy, which measures the energy loss of an electron beam within a transmission electron microscope when it interacts with a portion of a sample. The atom-probe tomograph has sub-nanometer resolution in 3-D and can chemically identify individual atoms using time-of-flight mass spectrometry.Spectra of excited states can be used to analyze the atomic composition of distant stars. Specific light wavelengths contained in the observed light from stars can be separated out and related to the quantized transitions in free gas atoms. These colors can be replicated using a gas-discharge lamp containing the same element. Helium was discovered in this way in the spectrum of the Sun 23 years before it was found on Earth.
Origin and current stateBaryonic matter forms about 4% of the total energy density of the observable Universe, with an average density of about 0.25 particles/m3 (mostly protons and electrons). Within a galaxy such as the Milky Way, particles have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 105 to 109 atoms/m3.CHOPPIN>FIRST=GREGORY R.
FormationElectrons 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 the beryllium and boron.Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasmaâa gas of positively charged ions (possibly, bare nuclei) and electrons. When the temperature drops below the ionization potential, atoms become statistically favorable. Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bangâan epoch called recombination, when the expanding Universe cooled enough to allow electrons to become attached to nuclei.Since the Big Bang, which produced no carbon or heavier elements, atomic nuclei have been combined in stars through the process of nuclear fusion to produce more of the element helium, and (via the triple alpha process) the sequence of elements from carbon up to iron; see stellar nucleosynthesis for details.Isotopes such as lithium-6, as well as some beryllium and boron are generated in space through cosmic ray spallation. This occurs when a high-energy proton strikes an atomic nucleus, causing large numbers of nucleons to be ejected.Elements heavier than iron were produced in supernovae through the r-process and in AGB stars through the s-process, both of which involve the capture of neutrons by atomic nuclei. Elements such as lead formed largely through the radioactive decay of heavier elements.
EarthMost of the atoms that make up the Earth 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.{{sfn|Manuel|2001|pp=407â430, 511â519}} Most of the helium in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of helium-3) is a product of alpha decay.There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere. Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions. Of the transuranic elementsâthose with atomic numbers greater than 92âonly plutonium and neptunium occur naturally on Earth. Transuranic elements have radioactive lifetimes shorter than the current age of the EarthZAIDER>FIRST1=MARCO
Rare and theoretical forms
Superheavy elementsWhile isotopes with atomic numbers higher than lead (82) are known to be radioactive, an "island of stability" has been proposed for some elements with atomic numbers above 103. These superheavy elements may have a nucleus that is relatively stable against radioactive decay. The most likely candidate for a stable superheavy atom, unbihexium, has 126 protons and 184 neutrons.
Exotic matterEach particle of matter has a corresponding antimatter particle with the opposite electrical charge. Thus, the positron is a positively charged antielectron and the antiproton is a negatively charged equivalent of a proton. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of this, along with an imbalance between the number of matter and antimatter particles, the latter are rare in the universe. The first causes of this imbalance are not yet fully understood, although theories of baryogenesis may offer an explanation. As a result, no antimatter atoms have been discovered in nature. However, in 1996 the antimatter counterpart of the hydrogen atom (antihydrogen) was synthesized at the CERN laboratory in Geneva.Other exotic atoms have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge. For example, an electron can be replaced by a more massive muon, forming a muonic atom. These types of atoms can be used to test the fundamental predictions of physics.
See also{hide}cmn|colwidth=21em|
- History of quantum mechanics
- Infinite divisibility
- List of basic chemistry topics
- Motion
- Timeline of atomic and subatomic physics
- Vector model of the atom
- Nuclear model
- Radioactive isotope
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, Zeghbroeck, WEB, Martin, W.C., Wiese, W.L., May 2007,weblink Atomic Spectroscopy: A Compendium of Basic Ideas, Notation, Data, and Formulas, National Institute of Standards and Technology, 8 January 2007,weblink" title="web.archive.org/web/20070208113156weblink">weblink 8 February 2007, live, WEB,weblink Atomic Emission Spectra â Origin of Spectral Lines, Avogadro Web Site, 10 August 2006, dead,weblink" title="web.archive.org/web/20060228231025weblink">weblink 28 February 2006, WEB, Fitzpatrick, Richard, 16 February 2007,weblink Fine structure, University of Texas at Austin, 14 February 2008,weblink 21 August 2011, live, WEB, Weiss, Michael, 2001,weblink The Zeeman Effect, University of California-Riverside, 6 February 2008,weblink" title="web.archive.org/web/20080202143147weblink">weblink 2 February 2008, live, WEB, Watkins, Thayer,weblink Coherence in Stimulated Emission, San José State University, 23 December 2007,weblink" title="web.archive.org/web/20080112234014weblink">weblink 12 January 2008, live, WEB, Reusch, William, 16 July 2007,weblink Virtual Textbook of Organic Chemistry, Michigan State University, 11 January 2008, dead,weblink" title="web.archive.org/web/20071029211245weblink">weblink 29 October 2007, WEB,weblink Covalent bonding â Single bonds, chemguide, 2000, 20 November 2008,weblink" title="web.archive.org/web/20081101203444weblink">weblink 1 November 2008, live, WEB, Husted, Robert, 11 December 2003,weblink Periodic Table of the Elements, Los Alamos National Laboratory, 11 January 2008,weblink" title="web.archive.org/web/20080110103232weblink">weblink 10 January 2008, live, etal, MAGAZINE, Rudy, Baum, 2003,weblink It's Elemental: The Periodic Table, Chemical & Engineering News, 11 January 2008,weblink 21 August 2011, live, JOURNAL, Brazhkin, Vadim V., Metastable phases, phase transformations, and phase diagrams in physics and chemistry, Physics-Uspekhi, 2006, 49, 7, 719â724, 10.1070/PU2006v049n07ABEH006013, 2006PhyU...49..719B, NEWS, Staff, 9 October 2001, Bose-Einstein Condensate: A New Form of Matter, National Institute of Standards and Technology,weblink 16 January 2008,weblink 3 January 2008, live, WEB, Colton, Imogen, Fyffe, Jeanette
, Bart J. Van
, 1998
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, Energy levels
, Shippensburg University
, 23 December 2007
, Bart J. Van
, 1998
,weblink" title="web.archive.org/web/20050115030639weblink">weblink
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, 23 December 2007
Further reading
External links{{Sister project links|voy=no|wikt=atom|v=The Atom|n=no|q=Atom|s=The New Student's Reference Work}}
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(Crain's) -- In one of the largest downtown leases of the year, Robert Morris University increased its space about 14%, to 323,000 square feet, as part of a long-term lease extension at its main campus at 401 S. State St.
University expands in downtown extension
Robert Morris extended its lease until 2024 in the 463,232-square-foot office building, giving the school about 70% of the structure. Its lease was to expire in 2017.
The school was little-known until 1998, when it moved to the bulky eight-story structure at the corner of State Street and Congress Parkway, which once housed a Sears, Roebuck and Co. store. But the South Loop location near Roosevelt University, Columbia College Chicago and the downtown campus of DePaul University helped the school flourish, expanding its enrollment and nearly doubling its space at 401 S. State, which houses classrooms room as well as administrative offices. The additional space will be used for a new library.
In addition to its main campus, Robert Morris has locations in Springfield, Peoria and six Chicago suburbs. Accredited in 1986, the four-year school was at 180 N. LaSalle St. before its move to State Street.
Robert Morris had total revenue of $112.7 million during the fiscal year ending June 30, 2008, according to its most recent tax return.
Compared to many other universities, Robert Morris has taken an unorthodox view toward real estate, preferring to rent rather than own. The original decision not to buy a building was less a matter of master strategy and more the result of the lower overall cost of leasing, says Joseph Learner, an executive vice-president in the Chicago office of tenant representation firm Studley Inc., which advises Robert Morris.
As a non-profit, Robert Morris wouldn't pay real estate taxes on property it owns. But even with property taxes, its overall costs are lower at 401 S. State.
"We've looked at it several times," Mr. Learner says. "Robert Morris has a philosophy of leasing."
Robert Morris President Michael Viollt says the prominent location of 401 S. State -- across the street from the Harold Washington Library Center and near public transportation -- is a key factor for the school.
The long-term leases allow the school to invest in building out its facilities, but the cost is less than if school owned the building.
"We put all our money into programs," Mr. Viollt says. "We wouldn't have the funds to do that if the money was tied up in bricks and mortar."
The building is owned by an affiliate of Willowbrook-based real estate firm Anvan Cos., whose founder, Anthony Antoniou, died in April. An Anvan executive did not return a call requesting comment.

subset: commoncrawl


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Dr. Ljungqvist is a specialist in the field of applied macroeconomic theory, with a focus on European unemployment and labor market institutions.
Dr. Iijma will present: Dispersed Behavior and Perceptions in Assortative Societies
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The Role of Memory in Search and Choice
Dr. Eisenbach research includes Financial Economics, Behavioral Economics, Microeconomic Theory
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Dr. Huangs research interest include Behavioral Economics, Experimental Economics, Applied Microeconomics, Decision Making, Negotiation, Gender
Dr. Marks will present his paper The Charitable Response to Tornadoes
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Dr. Wiczer research interest include macroeconomics and labor economics.
Dr. Herkenhoff's research interests include macroeconomics, applied macroeconomics, and real estate economics.
Dr. McEntarfer is the head of research and current acting program director for the Longitudinal Employer Household Dynamics program at the U.S. Census Bureau.


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Pastor Rik Krahn cames to Zion after serving 7 years as Associate Pastor at Martin Luther Church in Neenah, WI. He spent his Vicar year in Eagle River and Phelps, and graduated from Wisconsin Lutheran Seminary in 1996, after which he was assigned to be an Associate Pastor at First Lutheran Church in Lake Geneva, WI.
Pastor Krahn and his wife, Lori, are both life-long residents of Wisconsin – with Pastor growing up in Oconomowoc (between Milwaukee and Madison), and Lori in Kaukauna (just east of Appleton). Pastor has three children from his first marriage – Jordan, Emily and Levi – and Pastor and Lori together have two children – Caleb and Anna.
Lori enjoys music, photography, boating, scrapbooking and running/walking 5K's. Pastor enjoys watching and playing most sports (even though he's not very athletic), and stores a shocking amount of useless trivia.
Pastor Krahn recently accepted a call to Manitowoc Lutheran High School to head their Religion Program. He was installed in this new position on August 18, 2019. The members of Zion pray for God's blessing on Pastor Krahn and his family during his new service to his Lord.
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The city's child homicide rate is far greater than that of other cities of a similar size.Read more
AP News Articles
WASHINGTON (AP) — The Latest on President Donald Trump and the impeachment investigation (all times local):
6:20 p.m.
Acting White House chief of staff Mick Mulvaney says his comments about the Trump administration's decision to...Read more
WASHINGTON (AP) — The U.S. ambassador to the European Union told House impeachment investigators Thursday that President Donald Trump instructed him and other envoys to work with his personal lawyer, Rudy Giuliani, on Ukraine policy and that he was "disappointed" by the...Read more
ANKARA, Turkey (AP) — The Latest on developments in Syria (all times local):
4:50 a.m. Friday
The U.S. and Turkey have agreed to a cease-fire in the Turks' deadly attacks on Kurdish fighters in northern Syria, requiring the Kurds to...Read more
DETROIT (AP) — Striking General Motors workers will stay on the picket lines for at least another week until they vote on a tentative contract with the company.
Factory-level officials from the United Auto Workers union voted to recommend the agreement...Read more
LOS ANGELES (AP) — The vast catalog of storied Japanese animation house Studio Ghibli is heading to the new HBO Max streaming service.
Films such as "Princess Mononoke," ''My Neighbor Totoro" and Oscar-winner "Spirited Away" will be among the titles...Read more
CHICAGO (AP) — Striking teachers marched in picket lines outside hundreds of Chicago schools on Thursday after their union and city officials failed to reach a contract deal in the nation's third-largest school district, canceling classes for more than 300,000 students for...Read more
BEIRUT (AP) — The latest on Turkey's invasion of northern Syria (all times local):
03:15 a.m.
Australia has ruled out retrieving dozens of Australian women and children from refugee camps during the cease-fire in Syria....Read more
WASHINGTON (AP) — House Speaker Nancy Pelosi is plowing ahead with her bill to allow Medicare to negotiate prescription drug prices despite a breakdown in relations with her chief bargaining partner on the issue — President Donald Trump.
The nonpartisan...Read more
BALTIMORE (AP) — He stood up for the poor and the disadvantaged throughout urban America — but Elijah Cummings was principally the strong voice and political advocate for Baltimore, where he was revered as his hometown's champion.
The Democratic...Read more


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The Kalee Pedal Tractor comes with a working front loader, adjustable seat, front and rear trailer couplings, ackermann steering and enclosed chain drive. Pedals in forward and reverse with rubber traction strips.
Recommended age: 3+Max rider weight: 66 lbsProduct dimensions: 47x18x24 inBox Dimensions: 33x18x16 inBox Weight: 24 lbsWarranty: 30 days parts replacement
Children's Product Certificate
This product contains one or more chemicals, including lead, known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to http://www.p65warnings.ca.gov/
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How to Market a Venue Online: 7 Creative Ways to Advertise Your Event Space
Your venue is perfect. It has the location, the space, the amenities. But you have a lot of competition. Most cities are packed with awe-inspiring spaces, which means that there's no shortage of venue options for planners and clients. So what's the trick to marketing a venue so that the right people find it?
When it comes to event venue marketing, there are a few things that you can do.
Discover 7 Creative Ways to Improve Your Event Venue Online Marketing
1. Promote the area around your event venue for better marketing results
The things outside a venue can help it stand out. For example, your proximity to major tourist sites, central business areas, and major transport centers can attract event planners. In your marketing, highlight how these attractions around your venue can add value for attendees.
What kinds of local attractions and amenities make a difference? It's worth noting these things when marketing a venue:
- Courtyard spaces
- Waterfront access
- Grassy areas or parks
- Food districts
- Food truck hotspots
- Tourist sites
- Museums
- Train stations
- Airports
- Business districts
The key is to make it clear what amenities are outside your venue, and how they can benefit people who rent your space.
2. Set up a virtual tour to market your event venue
Most planners want to see a space before booking it, but it's not always possible for an event planner to come on site. In those cases, a virtual tour can help potential clients feel engaged with your event space and learn about what it offers.
As a marketing tool, a virtual tour lets planners experience your site without even setting foot in the building. The right venue marketing software will let you include all interactive photos and videos on your site, so planners can visualize their event in your space.
Here's one example: Harvard College's campus tour uses a great mix of text, photo, and video to provide helpful information. Even better, it gives viewers control over the experience. Alternatively, you can also use 360° technology, which provides a less structured tour, but gives event planners more freedom to "look around."
3. Photograph people, not just the space to drive more marketing leads for your event venue
Photographs are the easiest way to market off your event venue. Have you ever noticed that most marketing photos for venues have no people in them?
Showing people in your space helps planners understand what their real-life event could look like in your venue.
Try taking your promotional photos while an event is happening. Or, you could even stage an event for a photo shoot. Decorate the space to showcase its best features, move the furniture around, and ask or hire people to come in and mingle. This will liven up the photos and can help event planners make that crucial link between their event and your space.
You might be seeing increased competition from the new venue down the street. Or you have state of the art venue amenities and are wondering how to book more events business in the near future. Whatever the case may be for you and your venue, we have the low-down on how to market a venue. Here are our four lessons (and actions you can take) on brand awareness for venues.
4. Get social with your followers and promote your venue
Event venues have a huge advantage in social media content creation as they always have something new and different to promote and talk about. Use your current events, concerts, and shows to your advantage. Ensure an engaging social presence is a high-priority in your venue marketing efforts and create social assets that help you tell your story. Don't skimp on high-resolution videos and pictures, but make sure a joint promotion plan is OK with your clients before you start rolling. Always ask about their sharing boundaries.
Start with some before event planning information and pictures to show how what your venue has to offer. Then get some "boots on the ground" and capture the event in real time. Use the organizer's event hashtags and create engaging and compelling posts. Show your followers how amazing their event could be if they book your space.
5. Devise a digital advertising plan for your venue
In today's digital world the use of PPC and display advertising can never be underestimated.
One of the first places planners turn to find a venue for their event is via the web. Make sure you know how to effectively target your audience in the digital realm. This could include but isn't limited to search engines such as Google and Bing or social media outlets.
As a venue manager, you need to budget appropriately to compete with other venue spaces in your area. Knowing your target audience can help you zero in on unique keywords to optimize for that can help you stand out from the competition. For example, your city may be full of event venues. However, your venue is the only one with a rooftop.
Use display ads to entice planners who are actively looking for venues with rooftop space. Run promotions and test different ways to encourage click-throughs. It could be photos of the space, sweeping video walkthroughs, or even the past clients who have hosted an event there. Start with a small budget, test what sticks, then repeat it.
6. Network with the events community to drive business to your venue
Not everyone was born with the natural skill of networking. But don't worry: it's a skill that can be learned for both introverts and extroverts. For venue professionals, just know that it's definitely part of the job description.
When you're thinking of how to market a venue, think of networking as a means of generating word-of-mouth marketing. Show off the advantages of your venue that address a pain point that planners often experience to pique their interest. During a hectic event, it also helps to simply listen to the pain points planners to understand what they're looking for in a venue then follow up if your venue can solve their issues.
Wonder where you can get networking? Planner-based associations such as the ILEA, PCMA, or MPI are great places to meet planners.
7. Go rogue with venue guerilla marketing techniques (offline!)
If your venue is already filled with customers (for example, if you're a restaurant, brewery, or theater), you're in a prime position to take advantage of guerilla marketing. In-person marketing can be extremely effective, and venues are the perfect place to implement these type of marketing plans. Guerilla marketing takes an innovative approach to marketing, executed in-person or digitally as an experience for the target buyer.
In venue spaces, there are a lot of non-client/customer controlled spaces that are available to add a promotional touch. What if you posted up branding in areas such as bathrooms, lobbies, sidewalks, or foyers?
Now you know how to do event venue marketing online!
Up next, learn how to use Instagram to promote your event space. Or get creative ideas specifically for convention center event marketing.
How do you market your own venue? Let us know on Twitter @socialtables and on Facebook.


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Best furniture for Office and Home Dehradun
Niyash furniture studio has wide range of luxury dinning table, beds, home décor and much more. Niyash studio is bring in a new range for people who want to have their own style statement at their home. We also deal in Outdoor furniture for home and resorts . Get furniture with marble tops, gold finish and molded wood. You can also avail niyash studio membership by visiting store. for more details contact us at email@example.com or call us at: 7088375555 we provide only the best furniture.
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3818 Glen Vista Point
$1,100,000, .76 Acres
About This Property
Spectacular unobstructed views from Cheyenne Mountain to the south to Garden of the Gods, Pikes Peak and northwest on the front range - Great opportunity for one of the best lots left on the Vista - Build your Colorado dream home on this estate lot - Walkout lot - All the amenities of Kissing Camels are available to you.
Essential Information
Community Information
Lot Description
Hillside, Mountain View, View of Pikes Peak, See Prop Desc Remarks, View of Rock Formations
School Information
Additional Information
Listing Details
The real estate listing information and related content displayed on this site is provided exclusively for consumers' personal, non-commercial use and, may not be used for any purpose other than to identify prospective properties consumers may be interested in purchasing. This information and related content is deemed reliable but is not guaranteed accurate by the Pikes Peak REALTOR® Services Corp.


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Tips to Hire the Right Interactive Entertainment for Your Event.
We all know that entertainers can make or break events. Choosing the right one is critical if you would like to make the guests give you a "wow" response. Discover some of the ways that many people are using to ensure that the agency that they choose will make the best out of the day. Be sure to choose the group depending on the theme that you have selected for the day. If you complement the group with the kind of theme that you choose will be a great way of having the best day.
The age range your guests is important to be put into consideration. To help you come up with a customized event atmosphere, it is important that you can differentiate adults and children to ensure that you bring a tasteful experience, know the age bracket in the right manner. There are various performances that you may need to consider and choose wisely the live bands, fantastical arts and the usherette girls among others to ensure that you have the right procedures in the event.
Preparations are important, and this is whereby you do not get to visit the entertainers without a plan for your cash. Planning a budget might seem like an obvious thing, but it is going to impact the hiring process. You cannot know the affordable services when you do not even have an idea how much should be spent. No difference with what the entertainers will be offering now that they also need money out of what they do. You might and with very expensive entertainment services if you are not caution. Since the budget will include all the tasks to be done for the occasion, this is how you easily come up with the spending on entertainment. However, you can sacrifice some cash to get the best entertainment you will remember each day of your life.
If you like a certain entertainment crew, ask them about their charges and you can bargain since they do not have fixed prices. If you need the right services, then this should be about comparing the charges and select the one who has what you need. Also, getting to watch the entertainers as they do their thing is another tip to help you make up your mind. Also, the entertainers should give you their references. Although some entertainers will have so many references, you need to contact them so that you can be certain that they even exist.
Attributed by: https://www.gardengameshireuk.com/


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Betrayal Legacy Announced By Rob Daviau & Wizards Of The Coast
November 20, 2017 by brennon
Delving back into the realm of Legacy games we heard this weekend that Rob Daviau is joining forces with Wizards Of The Coast to bring Betrayal Legacy to life. A horror board game with a legacy twist - sounds exciting!
The original Betrayal at House on the Hill is quite a cult hit with board gamers. While it might not be the prettiest game out there it's a fun adventure akin to Scooby Doo meets, well, any horror movie ever. If you get a chance to play it, with its unique traitor mechanic, I'd recommend it.
The new version of the game will work based on the original concept but you will also bring in permanent changes to the game state and there will be a story arch you follow over many games.
You'll play through an introductory prologue and then a thirteen-chapter story which will cover multiple decades of in-game time.
Each player character will represent members of a family that may age and change as the game progresses - no doubt there's some business with a will and lots of (cursed) money!
Will you be picking this up?
"...no doubt there's some business with a will and lots of (cursed) money!"


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Data Compression and Security Chapter 20, Exploring the Digital Domain Digital Compression Concepts Compression techniques are used to replace a file with another that is smaller Decompression techniques expands the compressed file to recover original data -- exactly or in facsimile A pair of compression/decompression techniques that work together is called a codec for short Types of Codecs Codecs that upon decompression always reproduce the original file exactly are called lossless codecs Codecs that reproduce only an approximation of the original file upon decompression are called lossy codecs Codecs that take approximately the same amount of time to compress and decompress a file are referred to as symmetric codecs By contrast, codecs that feature simple fast decompression but significantly slower compression are called asymmetric codecs Compression Encoding Compression is an encoding process that filters the original file in several successive stages Codec Methods Syntactic encoding (also called entropy encoding) methods attempt to reduce the redundancy of symbolic patterns in a file without any regard to the type of information represented Semantic methods consider special properties of the type of information represented to reduce nonessential information in a file Hybrid methods combine both syntactic and semantic methods Compressing Text and Numerical Data Lossless Syntactic Methods Run-Length Encoding (RLE) looks for repeated sequences of symbols widely used for fax (facsimile) transmissions Huffman Codes exploits frequency distribution of symbols in a source adaptive Huffman coding builds its own frequency tables rather than use predefined statistics Lempel-Ziv-Welch (LZW) compression based on recognizing patterns of strings in original file fast and yields good results (50% typical reduction) Compressing Images GIF (Graphic Interchange Format) Codec employs LZW method for lossless compression TIFF (Tagged Image File Format) Codec lossless syntactic method JPEG (Joint Photographics Experts Group) Codec umbrella term covering several lossy and lossless methods baseline method is most commonly used one -lossy method based on a hybrid method Compressing Video Video compression employs both spatial and temporal compression spatial techniques compress individual frames temporal methods compress data in frames over time QuickTime and AVI (Audio Video Interleaved) are two popular (and incompatible with each other) formats Compressing Video Some Additional Methods DVI (Digital Video Interactive) Motion-JPEG MPEG (Motion Pictures Experts Group) The px64 Standard Temporal Compression in Video Lossy strategies for eliminating redundancy of information between frames employ temporal compression -- referred to as interframe compression Sequence of frames are considered together key frames difference frames Used in QuickTime and DVI Temporal Video Compression (cont'd) MPEG and related codecs employ a more complex frame-referencing method intrapictures (I pictures) predicted pictures (P pictures) bidirectional pictures (B pictures) Compressing Audio A widely used method is ADPCM (Adaptive Differential Pulse Code Modulation) ADPCM lossy method employs a differencing technique related to those used in video compression used in DVI MP3 employs psychoacoustic methods filter out parts of the signal most people do not hear uses methods to measure the amount of quantization that will just mask noise Encryption and Data Security Cryptography is the art and science of keeping message secret Encryption techniques convert data into a secret code for transmission The process of retrieving the original message at the receiver is called decryption Encryption Keys Keys are essential information -- usually a numerical parameter(s) -- needed for encryption and/or decryption algorithms Encryption keys are used to encode plaintext as encoded ciphertext Decryption keys are used to decode ciphertext and recover the original plaintext Decryption keys are sometimes discovered by brute force methods employing computers to search large potential key spaces Symmetric or Secret Key Ciphers Secret key ciphers use a single secret key (or set of keys) for both encryption and decryption The secret key must be transferred securely in order for secret key methods to be secure Data Encryption Standard (DES) is a US government sponsored secret key cipher. DES uses a 56-bit key. International Data Encryption Algorithm (IDEA) has been proposed to replace DES. It uses a 128-bit key. Longer keys make it more difficult for brute force discovery of the secret key Asymmetric or Public Key Ciphers The first practical public key algortihm was published by Rivest, Shamir, and Adleman in 1976 and is know as RSA (for their last names) Public key ciphers employ an algortihm with two keys -- a public key and a private key A sender looks up the recipient's public key and uses it to encode a message The recipient then decodes the message with his or her private key (this private key is necessary to decode the message) Asymmetric or Public Key Ciphers Illustrated More on Public Key Methods No attempt is made to keep secret the actual encryption and decryption algorithms for public key methods -- security depends on only the recipient knowing his or her private key Public key ciphers are more secure than secret key ciphers, but are not as efficient since they require longer keys and more computing in the encryption and decryption processes For sake of efficiency, sometimes secret key encryption is used and the secret key is communicated employing public key methods -the combination of a secret key encoded message and public key encoded value of the secret key is called a digital envelope Authentication The process used to verify the identity of a respondent is called authentication Authentication is very important for electronic commerce and other network transactions Authentication exploits the symmetry of public and private keys To authenticate that a person is who they say they are: send that person a nonsense message and ask them to encode it with their private key and return it to you when the message is returned, if the person is who they claim to be, you should be able to recover your nonsense message using their public key (which presumably you know) Encryption and National Security An escrowed secret key cipher is a secret key cipher in which a trusted third party controls the secret key. DES is an example of such a cipher, and the US government holds the escrowed 56-bit secret key The International Trafficking in Arms Regulation (ITAR) prohibits the export of secret key cipher systems with secret keys longer than 40 bits Encryption and National Security A major governments can break ciphers with 40-bit or shorter keys by brute force Limiting longer secret key ciphers is an attempt to retain the ability to break codes when this is deemed necessary for national security The ITAR law has been debated for a number of years Public key ciphers have complicated the debate further -and it continues The basic issue is privacy versus the national security Summary Compressing data means reducing the effective size of a data file for storage or transmission Particular paired compression/decompression methods are called codecs Codecs that cannot reproduce the original file exactly are called lossy methods; those that reproduce the original exactly are called lossless methods Text and numbers usually require lossless methods Images, video, and sound codecs are usually lossy Summary (cont'd) Syntactic methods attempt to reduce the redundancy of symbolic patterns in a file without any regard to the type of information represented Semantic methods exploit characteristics inherent in the type of information being represented The use of codecs is not an exact science -- the effectiveness and suitability of any method will depend on the exact nature of the original file and the intended use for the compressed file Summary (cont'd) With the increasing access to and ease of transmitting sensitive and confidential information come significant security risks Encryption techniques are used to encode messages for secure transmission The two primary encryption/decryption methods are: secret key (symmetric key) ciphers public key (asymmetric key) ciphers Summary (cont'd) Public key ciphers are more secure, but secret key ciphers are more efficient Public key encryption is used for authentication over computer networks An active national (and international) debate continues over government control and regulation of encryption/decryption methods