1.
Jmol
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Jmol is computer software for molecular modelling chemical structures in 3-dimensions. Jmol returns a 3D representation of a molecule that may be used as a teaching tool and it is written in the programming language Java, so it can run on the operating systems Windows, macOS, Linux, and Unix, if Java is installed. It is free and open-source software released under a GNU Lesser General Public License version 2.0, a standalone application and a software development kit exist that can be integrated into other Java applications, such as Bioclipse and Taverna. A popular feature is an applet that can be integrated into web pages to display molecules in a variety of ways, for example, molecules can be displayed as ball-and-stick models, space-filling models, ribbon diagrams, etc. Jmol supports a range of chemical file formats, including Protein Data Bank, Crystallographic Information File, MDL Molfile. There is also a JavaScript-only version, JSmol, that can be used on computers with no Java, the Jmol applet, among other abilities, offers an alternative to the Chime plug-in, which is no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS9. Jmol requires Java installation and operates on a variety of platforms. For example, Jmol is fully functional in Mozilla Firefox, Internet Explorer, Opera, Google Chrome, fast and Scriptable Molecular Graphics in Web Browsers without Java3D
2.
ChemSpider
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ChemSpider is a database of chemicals. ChemSpider is owned by the Royal Society of Chemistry, the database contains information on more than 50 million molecules from over 500 data sources including, Each chemical is given a unique identifier, which forms part of a corresponding URL. This is an approach to develop an online chemistry database. The search can be used to widen or restrict already found results, structure searching on mobile devices can be done using free apps for iOS and for the Android. The ChemSpider database has been used in combination with text mining as the basis of document markup. The result is a system between chemistry documents and information look-up via ChemSpider into over 150 data sources. ChemSpider was acquired by the Royal Society of Chemistry in May,2009, prior to the acquisition by RSC, ChemSpider was controlled by a private corporation, ChemZoo Inc. The system was first launched in March 2007 in a release form. ChemSpider has expanded the generic support of a database to include support of the Wikipedia chemical structure collection via their WiChempedia implementation. A number of services are available online. SyntheticPages is an interactive database of synthetic chemistry procedures operated by the Royal Society of Chemistry. Users submit synthetic procedures which they have conducted themselves for publication on the site and these procedures may be original works, but they are more often based on literature reactions. Citations to the published procedure are made where appropriate. They are checked by an editor before posting. The pages do not undergo formal peer-review like a journal article. The comments are moderated by scientific editors. The intention is to collect practical experience of how to conduct useful chemical synthesis in the lab, while experimental methods published in an ordinary academic journal are listed formally and concisely, the procedures in ChemSpider SyntheticPages are given with more practical detail. Comments by submitters are included as well, other publications with comparable amounts of detail include Organic Syntheses and Inorganic Syntheses
3.
European Chemicals Agency
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ECHA is the driving force among regulatory authorities in implementing the EUs chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and it is located in Helsinki, Finland. The Agency, headed by Executive Director Geert Dancet, started working on 1 June 2007, the REACH Regulation requires companies to provide information on the hazards, risks and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most commonly used substances have been registered, the information is technical but gives detail on the impact of each chemical on people and the environment. This also gives European consumers the right to ask whether the goods they buy contain dangerous substances. The Classification, Labelling and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU. This worldwide system makes it easier for workers and consumers to know the effects of chemicals, companies need to notify ECHA of the classification and labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100000 substances, the information is freely available on their website. Consumers can check chemicals in the products they use, Biocidal products include, for example, insect repellents and disinfectants used in hospitals. The Biocidal Products Regulation ensures that there is information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation, the law on Prior Informed Consent sets guidelines for the export and import of hazardous chemicals. Through this mechanism, countries due to hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have effects on human health and the environment are identified as Substances of Very High Concern 1. These are mainly substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment, other substances considered as SVHCs include, for example, endocrine disrupting chemicals. Companies manufacturing or importing articles containing these substances in a concentration above 0 and they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy, once a substance has been officially identified in the EU as being of very high concern, it will be added to a list. This list is available on ECHA’s website and shows consumers and industry which chemicals are identified as SVHCs, Substances placed on the Candidate List can then move to another list
4.
PubChem
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PubChem is a database of chemical molecules and their activities against biological assays. The system is maintained by the National Center for Biotechnology Information, a component of the National Library of Medicine, PubChem can be accessed for free through a web user interface. Millions of compound structures and descriptive datasets can be downloaded via FTP. PubChem contains substance descriptions and small molecules with fewer than 1000 atoms and 1000 bonds, more than 80 database vendors contribute to the growing PubChem database. PubChem consists of three dynamically growing primary databases, as of 28 January 2016, Compounds,82.6 million entries, contains pure and characterized chemical compounds. Substances,198 million entries, contains also mixtures, extracts, complexes, bioAssay, bioactivity results from 1.1 million high-throughput screening programs with several million values. PubChem contains its own online molecule editor with SMILES/SMARTS and InChI support that allows the import and export of all common chemical file formats to search for structures and fragments. In the text search form the database fields can be searched by adding the name in square brackets to the search term. A numeric range is represented by two separated by a colon. The search terms and field names are case-insensitive, parentheses and the logical operators AND, OR, and NOT can be used. AND is assumed if no operator is used, example,0,5000,50,10 -5,5 PubChem was released in 2004. The American Chemical Society has raised concerns about the publicly supported PubChem database and they have a strong interest in the issue since the Chemical Abstracts Service generates a large percentage of the societys revenue. To advocate their position against the PubChem database, ACS has actively lobbied the US Congress, soon after PubChems creation, the American Chemical Society lobbied U. S. Congress to restrict the operation of PubChem, which they asserted competes with their Chemical Abstracts Service
5.
International Chemical Identifier
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Initially developed by IUPAC and NIST from 2000 to 2005, the format and algorithms are non-proprietary. The continuing development of the standard has supported since 2010 by the not-for-profit InChI Trust. The current version is 1.04 and was released in September 2011, prior to 1.04, the software was freely available under the open source LGPL license, but it now uses a custom license called IUPAC-InChI Trust License. Not all layers have to be provided, for instance, the layer can be omitted if that type of information is not relevant to the particular application. InChIs can thus be seen as akin to a general and extremely formalized version of IUPAC names and they can express more information than the simpler SMILES notation and differ in that every structure has a unique InChI string, which is important in database applications. Information about the 3-dimensional coordinates of atoms is not represented in InChI, the InChI algorithm converts input structural information into a unique InChI identifier in a three-step process, normalization, canonicalization, and serialization. The InChIKey, sometimes referred to as a hashed InChI, is a fixed length condensed digital representation of the InChI that is not human-understandable. The InChIKey specification was released in September 2007 in order to facilitate web searches for chemical compounds and it should be noted that, unlike the InChI, the InChIKey is not unique, though collisions can be calculated to be very rare, they happen. In January 2009 the final 1.02 version of the InChI software was released and this provided a means to generate so called standard InChI, which does not allow for user selectable options in dealing with the stereochemistry and tautomeric layers of the InChI string. The standard InChIKey is then the hashed version of the standard InChI string, the standard InChI will simplify comparison of InChI strings and keys generated by different groups, and subsequently accessed via diverse sources such as databases and web resources. Every InChI starts with the string InChI= followed by the version number and this is followed by the letter S for standard InChIs. The remaining information is structured as a sequence of layers and sub-layers, the layers and sub-layers are separated by the delimiter / and start with a characteristic prefix letter. The six layers with important sublayers are, Main layer Chemical formula and this is the only sublayer that must occur in every InChI. The atoms in the formula are numbered in sequence, this sublayer describes which atoms are connected by bonds to which other ones. Describes how many hydrogen atoms are connected to each of the other atoms, the condensed,27 character standard InChIKey is a hashed version of the full standard InChI, designed to allow for easy web searches of chemical compounds. Most chemical structures on the Web up to 2007 have been represented as GIF files, the full InChI turned out to be too lengthy for easy searching, and therefore the InChIKey was developed. With all databases currently having below 50 million structures, such duplication appears unlikely at present, a recent study more extensively studies the collision rate finding that the experimental collision rate is in agreement with the theoretical expectations. Example, Morphine has the structure shown on the right, as the InChI cannot be reconstructed from the InChIKey, an InChIKey always needs to be linked to the original InChI to get back to the original structure
6.
Simplified molecular-input line-entry system
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The simplified molecular-input line-entry system is a specification in form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules, the original SMILES specification was initiated in the 1980s. It has since modified and extended. In 2007, a standard called OpenSMILES was developed in the open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. The Environmental Protection Agency funded the project to develop SMILES. It has since modified and extended by others, most notably by Daylight Chemical Information Systems. In 2007, a standard called OpenSMILES was developed by the Blue Obelisk open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, in July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is generally considered to have the advantage of being slightly more human-readable than InChI, the term SMILES refers to a line notation for encoding molecular structures and specific instances should strictly be called SMILES strings. However, the term SMILES is also used to refer to both a single SMILES string and a number of SMILES strings, the exact meaning is usually apparent from the context. The terms canonical and isomeric can lead to confusion when applied to SMILES. The terms describe different attributes of SMILES strings and are not mutually exclusive, typically, a number of equally valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol, algorithms have been developed to generate the same SMILES string for a given molecule, of the many possible strings, these algorithms choose only one of them. This SMILES is unique for each structure, although dependent on the algorithm used to generate it. These algorithms first convert the SMILES to a representation of the molecular structure. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database, there is currently no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, and these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES
7.
Chemical formula
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These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
8.
Density
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The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
9.
Melting point
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The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
10.
Boiling point
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The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the environmental pressure. A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a boiling point than when that liquid is at atmospheric pressure. For a given pressure, different liquids boil at different temperatures, for example, water boils at 100 °C at sea level, but at 93.4 °C at 2,000 metres altitude. The normal boiling point of a liquid is the case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level,1 atmosphere. At that temperature, the pressure of the liquid becomes sufficient to overcome atmospheric pressure. The standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar, the heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation, evaporation is a surface phenomenon in which molecules located near the liquids edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, a saturated liquid contains as much thermal energy as it can without boiling. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase, the liquid can be said to be saturated with thermal energy. Any addition of energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed, similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the pressure of the liquid equals the surrounding environmental pressure. Thus, the point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, at higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased pressure up to the critical point, the boiling point cannot be increased beyond the critical point. Likewise, the point decreases with decreasing pressure until the triple point is reached
11.
Aqueous solution
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An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending to the relevant chemical formula, for example, a solution of table salt, or sodium chloride, in water would be represented as Na+ + Cl−. The word aqueous means pertaining to, related to, similar to, as water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Substances that are hydrophobic often do not dissolve well in water, an example of a hydrophilic substance is sodium chloride. Acids and bases are aqueous solutions, as part of their Arrhenius definitions, the ability of a substance to dissolve in water is determined by whether the substance can match or exceed the strong attractive forces that water molecules generate between themselves. If the substance lacks the ability to dissolve in water the molecules form a precipitate, reactions in aqueous solutions are usually metathesis reactions. Metathesis reactions are another term for double-displacement, that is, when a cation displaces to form a bond with the other anion. The cation bonded with the latter anion will dissociate and bond with the other anion, aqueous solutions that conduct electric current efficiently contain strong electrolytes, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are ionized in water. Nonelectrolytes are substances that dissolve in water yet maintain their molecular integrity, examples include sugar, urea, glycerol, and methylsulfonylmethane. When writing the equations of reactions, it is essential to determine the precipitate. To determine the precipitate, one must consult a chart of solubility, soluble compounds are aqueous, while insoluble compounds are the precipitate. Remember that there may not always be a precipitate, when performing calculations regarding the reacting of one or more aqueous solutions, in general one must know the concentration, or molarity, of the aqueous solutions. Solution concentration is given in terms of the form of the prior to it dissolving. Metal ions in aqueous solution Solubility Dissociation Acid-base reaction theories Properties of water Zumdahl S.1997, 4th ed. Boston, Houghton Mifflin Company
12.
Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
13.
Hexagonal crystal family
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In crystallography, the hexagonal crystal family is one of the 6 crystal families. In the hexagonal family, the crystal is described by a right rhombic prism unit cell with two equal axes, an included angle of 120° and a height perpendicular to the two base axes. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral, the hexagonal crystal family consists of two lattice systems, hexagonal and rhombohedral. Each lattice system consists of one Bravais lattice, hence, there are 3 lattice points per unit cell in total and the lattice is non-primitive. The Bravais lattices in the hexagonal crystal family can also be described by rhombohedral axes, the unit cell is a rhombohedron. This is a cell with parameters a = b = c, α = β = γ ≠ 90°. In practice, the description is more commonly used because it is easier to deal with a coordinate system with two 90° angles. However, the axes are often shown in textbooks because this cell reveals 3m symmetry of crystal lattice. However, such a description is rarely used, the hexagonal crystal family consists of two crystal systems, trigonal and hexagonal. A crystal system is a set of point groups in which the point groups themselves, the trigonal crystal system consists of the 5 point groups that have a single three-fold rotation axis. The crystal structures of alpha-quartz in the example are described by two of those 18 space groups associated with the hexagonal lattice system. The hexagonal crystal system consists of the seven point groups such that all their groups have the hexagonal lattice as underlying lattice. Graphite is an example of a crystal that crystallizes in the crystal system. Note that the atom in the center of the HCP unit cell in the hexagonal lattice system does not appear in the unit cell of the hexagonal lattice. It is part of the two atom motif associated with each point in the underlying lattice. The trigonal crystal system is the crystal system whose point groups have more than one lattice system associated with their space groups. The 5 point groups in this system are listed below, with their international number and notation, their space groups in name. The point groups in this system are listed below, followed by their representations in Hermann–Mauguin or international notation and Schoenflies notation
14.
Occupational safety and health
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These terms of course also refer to the goals of this field, so their use in the sense of this article was originally an abbreviation of occupational safety and health program/department etc. The goals of occupational safety and health programs include to foster a safe, OSH may also protect co-workers, family members, employers, customers, and many others who might be affected by the workplace environment. In the United States, the occupational health and safety is referred to as occupational health and occupational and non-occupational safety. In common-law jurisdictions, employers have a common law duty to take care of the safety of their employees. As defined by the World Health Organization occupational health deals with all aspects of health, Health has been defined as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. Occupational health is a field of healthcare concerned with enabling an individual to undertake their occupation. Health has been defined as It contrasts, for example, with the promotion of health and safety at work, since 1950, the International Labour Organization and the World Health Organization have shared a common definition of occupational health. It was adopted by the Joint ILO/WHO Committee on Occupational Health at its first session in 1950, the concept of working culture is intended in this context to mean a reflection of the essential value systems adopted by the undertaking concerned. Such a culture is reflected in practice in the systems, personnel policy, principles for participation, training policies. Professionals advise on a range of occupational health matters. The research and regulation of safety and health are a relatively recent phenomenon. As labor movements arose in response to concerns in the wake of the industrial revolution. The initial remit of the Inspectorate was to police restrictions on the hours in the textile industry of children. The commission sparked public outrage resulted in the Mines Act of 1842. Otto von Bismarck inaugurated the first social insurance legislation in 1883, similar acts followed in other countries, partly in response to labor unrest. Although work provides many economic and other benefits, an array of workplace hazards also present risks to the health. Personal protective equipment can protect against many of these hazards. Physical hazards affect many people in the workplace, Falls are also a common cause of occupational injuries and fatalities, especially in construction, extraction, transportation, healthcare, and building cleaning and maintenance
15.
GHS hazard pictograms
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Hazard pictograms form part of the international Globally Harmonized System of Classification and Labelling of Chemicals. Two sets of pictograms are included within the GHS, one for the labelling of containers and for workplace hazard warnings, either one or the other is chosen, depending on the target audience, but the two are not used together. The two sets of use the same symbols for the same hazards, although certain symbols are not required for transport pictograms. Transport pictograms come in variety of colors and may contain additional information such as a subcategory number. It has still to be implemented by the European Union in 2009, the following pictograms are included in the Worldwide Model Using but have not been incorporated into the GHS, ICZ and Catwallsh Hazcom Labelling because of the nature of the hazards. Globally Harmonized System of Classification and Labelling of Chemicals, New York and Geneva, United Nations,2007, ISBN 978-92-1-116957-7, ST/SG/AC. 10/30/Rev. Model Regulations, New York and Geneva, United Nations,2007, ISBN 978-92-1-139120-6, manual of Tests and Criteria, New York and Geneva, United Nations,2002, ISBN 92-1-139087-7, ST/SG/AC. 10/11/Rev.4 GHS pictogram gallery from the United Nations Economic Commission for Europe
16.
Ion
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An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by chemical or physical means. In chemical terms, if an atom loses one or more electrons. If an atom gains electrons, it has a net charge and is known as an anion. Ions consisting of only a single atom are atomic or monatomic ions, because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of ionization of a medium, such as a gas, which are known as ion pairs are created by ion impact, and each pair consists of a free electron. The word ion comes from the Greek word ἰόν, ion, going and this term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday also introduced the words anion for a charged ion. In Faradays nomenclature, cations were named because they were attracted to the cathode in a galvanic device, arrhenius explanation was that in forming a solution, the salt dissociates into Faradays ions. Arrhenius proposed that ions formed even in the absence of an electric current, ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of charge to give neutral molecules or ionic salts. These stabilized species are commonly found in the environment at low temperatures. A common example is the present in seawater, which are derived from the dissolved salts. Electrons, due to their mass and thus larger space-filling properties as matter waves, determine the size of atoms. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other, as such, in general, cations are smaller than the corresponding parent atom or molecule due to the smaller size of its electron cloud. One particular cation contains no electrons, and thus consists of a single proton - very much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, an anion, from the Greek word ἄνω, meaning up, is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κατά, meaning down, is an ion with fewer electrons than protons, there are additional names used for ions with multiple charges
17.
Ammonium nitrite
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Ammonium nitrite, NH4NO2, is the ammonia salt of nitrous acid. It is not used in isolated form, since it is highly unstable and decomposes into water. Ammonium nitrite forms naturally in the air and can be prepared by the absorption of equal parts nitrogen dioxide, the precipitate is filtered off and the solution concentrated. It forms colorless crystals which are soluble in water, but decomposes when heated or in the presence of acid into water, Ammonium nitrite solution is stable at higher pH and lower temperature. If there is any decrease in pH lower than 7.0, a safe pH can be maintained by adding an ammonia solution. The mole ratio of ammonium nitrite to ammonia must be above 10%, NH4NO2 → N2 +2 H2O Ammonium nitrite may explode at a temperature of 60–70 °C, and will decompose quicker when dissolved in a concentrated aqueous solution, than in the form of a dry crystal
18.
Sodium nitrate
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Sodium nitrate is the chemical compound with the formula NaNO3. This alkali metal salt is also known as Peru saltpeter to distinguish it from ordinary saltpeter. The mineral form is known as nitratine, nitratite or soda niter. Sodium nitrate is a solid very soluble in water. It has been mined extensively for these purposes, with time, however, the mining of South American saltpeter became a profitable business. Chile fought against the allies Peru and Bolivia in the War of the Pacific 1879-1884, in 1919, Ralph Walter Graystone Wyckoff determined its crystal structure using X-ray crystallography. The largest accumulations of naturally occurring sodium nitrate are found in Chile and Peru, by the 1940s, this conversion process resulted in a dramatic decline in demand for sodium nitrate procured from natural sources. Chile still has the largest reserves of caliche, with mines in such locations as Pedro de Valdivia, María Elena and Pampa Blanca. Sodium nitrate, potassium nitrate, sodium sulfate and iodine are all obtained by the processing of caliche, the former Chilean saltpeter mining communities of Humberstone and Santa Laura were declared Unesco World Heritage sites in 2005. It can be combined with iron hydroxide to make a synthetic resin, sodium nitrate can be combined with sulfuric acid and nitric acid distilled off. At lower pressure the temperature needed results in less decomposition. The theoretical 2 moles of nitric acid per 1 mole of sulfuric acid results in a high end temperature, much decomposition. When this reaction was important industrially, it was practice to operate with sulfuric acid in excess to end on a mostly bisulfate product poured molten out of the retort. Hobbyist gold refiners use sodium nitrate to make a hybrid aqua regia that dissolves gold, sodium nitrate is also a food additive used as a preservative and color fixative in cured meats and poultry, it is listed under its INS number 251 or E number E251. It is approved for use in the EU, USA and Australia, sodium nitrate should not be confused with sodium nitrite, which is also a common food additive and preservative used, for example, in deli meats. Less common applications include as an oxidizer in fireworks, replacing potassium nitrate commonly found in black powder, sodium nitrate is used together with potassium nitrate and calcium nitrate for heat storage and, more recently, for heat transfer in solar power plants. A mixture of sodium nitrate, calcium nitrate and potassium nitrate is used as material in prototype plants, such as Andasol Solar Power Station. It is also used in the industry for facultative microorganism respiration
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Potassium nitrate
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Potassium nitrate is a chemical compound with the chemical formula KNO3. It is a salt of potassium ions K+ and nitrate ions NO3−. It occurs as a mineral niter and is a solid source of nitrogen. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter or saltpetre, major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks. It is one of the constituents of gunpowder and has been used since the Middle Ages as a food preservative. Potassium nitrate, because of its early and global use and production, has many names, by the 15th century, Europeans referred to it as saltpeter and later as nitrate of potash, as the chemistry of the compound was more fully understood. The Arabs called it Chinese snow and it was called Chinese salt by the Iranians/Persians or salt from Chinese salt marshes. Potassium nitrate has a crystal structure at room temperature, which transforms to a trigonal system at 129 °C. Potassium nitrate is soluble in water, but its solubility increases with temperature. The aqueous solution is almost neutral, exhibiting pH6.2 at 14 °C for a 10% solution of commercial powder and it is not very hygroscopic, absorbing about 0. 03% water in 80% relative humidity over 50 days. It is insoluble in alcohol and is not poisonous, it can react explosively with reducing agents and this was used for the manufacture of gunpowder and explosive devices. The terminology used by al-Rammah indicated a Chinese origin for the gunpowder weapons about which he wrote, at least as far back as 1845, Chilean saltpeter deposits were exploited in Chile and California, USA. A major natural source of nitrate was the deposits crystallizing from cave walls. Extraction is accomplished by immersing the guano in water for a day, filtering, traditionally, guano was the source used in Laos for the manufacture of gunpowder for Bang Fai rockets. Perhaps the most exhaustive discussion of the production of material is the 1862 LeConte text. He was writing with the purpose of increasing production in the Confederate States to support their needs during the American Civil War. Since he was calling for the assistance of rural farming communities and he details the French Method, along with several variations, as well as a Swiss method. Many references have been made to a method using only straw and urine, LeConte describes a process using only urine and not dung, referring to it as the Swiss method
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Hydroxylammonium nitrate
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Hydroxylammonium nitrate or hydroxylamine nitrate is an inorganic compound with the chemical formula NH3OHNO3. It is a derived from hydroxylamine and nitric acid. In its pure form, it is a hygroscopic solid. It has potential to be used as a rocket propellant either as a solution in monopropellants or bipropellants, the compound is a salt with separated hydroxyammonium and nitrate ions. Hydroxylammonium nitrate is unstable because it both a reducing agent and an oxidizer, the situation being analogous to ammonium nitrate. It is usually handled as an aqueous solution, the solution is corrosive and toxic, and may be carcinogenic. Solid HAN is unstable, particularly in the presence of trace amounts of metal salts and it is typically bonded with glycidyl azide polymer, hydroxyl-terminated polybutadiene, or carboxy-terminated polybutadiene and requires preheating to 200-300 °C to decompose. The catalyst is a metal, similar to the other monopropellants that use silver or palladium. It will be used in a fuel/oxidizer blend known as AF-M315E in the high thrust engines of the Green Propellant Infusion Mission in 2017, the specific impulse of AF-M315E is 257 s. The aqueous solution of HAN can be added with fuel components such us Methanol, Glycine, TEAN, HAN is sometimes used in nuclear reprocessing as a reducing agent for plutonium ions. The kinetics and mechanism of oxidation of hydroxylamine by iron
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Ammonium perchlorate
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Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is a colorless or white solid that is soluble in water, perchlorate is a powerful oxidizer and ammonium is a good fuel. This combination explains the usefulness of this material as a rocket propellant and its instability has involved it in a number of accidents, such as the PEPCON disaster. Ammonium perchlorate is produced by reaction between ammonia and perchloric acid and this process is the main outlet for the industrial production of perchloric acid. The salt also can be produced by metathesis reaction of ammonium salts with sodium perchlorate. This process exploits the low solubility of NH4ClO4, which is about 10% of that for sodium perchlorate. Like most ammonium salts, ammonium perchlorate decomposes before melting, mild heating results in production of hydrogen chloride, nitrogen, oxygen, and water. 4 NH4ClO4 →4 HCl +2 N2 +5 O2 +6 H2O The combustion of AP is quite complex and is widely studied, AP crystals decompose before melting, even though a thin liquid layer has been observed on crystal surfaces during high-pressure combustion processes. Strong heating may lead to explosions, pure crystals cannot sustain a flame below the pressure of 2 MPa. AP is a Class 4 oxidizer for particle sizes over 15 micrometres and is classified as an explosive for particle sizes less than 15 micrometres, the primary use of ammonium perchlorate is in making solid fuel propellants. When AP is mixed with a fuel, it can generate self-sustained combustion at far under atmospheric pressure. It is an important oxidizer with a history of use in solid rocket propellants — space launch, military, amateur. Some breakable epoxy adhesives contain suspensions of AP, upon heating to 300 °C, the AP degrades the organic adhesive, breaking the cemented joint. Perchlorate itself confers little acute toxicity, for example, sodium perchlorate has an LD50 of 2-4 g/kg and is eliminated rapidly after ingestion. However, chronic exposure to perchlorates, even in low concentrations, has shown to cause various thyroid problems
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Chemical compound
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A chemical compound is an entity consisting of two or more atoms, at least two from different elements, which associate via chemical bonds. Many chemical compounds have a numerical identifier assigned by the Chemical Abstracts Service. For example, water is composed of two atoms bonded to one oxygen atom, the chemical formula is H2O. A compound can be converted to a different chemical composition by interaction with a chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AC + BD, where A, B, C, and D are each unique atoms, and AB, CD, AC, and BD are each unique compounds. A chemical element bonded to a chemical element is not a chemical compound since only one element. Examples are the diatomic hydrogen and the polyatomic molecule sulfur. Chemical compounds have a unique and defined chemical structure held together in a spatial arrangement by chemical bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms. There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Characteristic properties of compounds include that elements in a compound are present in a definite proportion, for example, the molecule of the compound water is composed of hydrogen and oxygen in a ratio of 2,1. In addition, compounds have a set of properties. The physical and chemical properties of compounds differ from those of their constituent elements, however, mixtures can be created by mechanical means alone, but a compound can be created only by a chemical reaction. Some mixtures are so combined that they have some properties similar to compounds. Other examples of compound-like mixtures include intermetallic compounds and solutions of metals in a liquid form of ammonia. Compounds may be described using formulas in various formats, for compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the elements in a chemical formula are normally listed in a specific order, called the Hill system
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Nitrate
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Nitrate is a polyatomic ion with the molecular formula NO−3 and a molecular mass of 62.0049 g/mol. Nitrates also describe the functional group RONO2. These nitrate esters are a class of explosives. The anion is the base of nitric acid, consisting of one central nitrogen atom surrounded by three identically bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a charge of −1. This arrangement is used as an example of resonance. Like the isoelectronic carbonate ion, the ion can be represented by resonance structures. A common example of a nitrate salt is potassium nitrate. A rich source of nitrate in the human body comes from diets rich in leafy green foods, such as spinach. NO3- is the active component within beetroot juice and other vegetables. Nitrite and water are converted in the body to nitric oxide, nitrate salts are found naturally on earth as large deposits, particularly of nitratine, a major source of sodium nitrate. Nitrates are found in man-made fertilizers, as a byproduct of lightning strikes in earths nitrogen-oxygen rich atmosphere, nitric acid is produced when nitrogen dioxide reacts with water vapor. Nitrates are mainly produced for use as fertilizers in agriculture because of their solubility and biodegradability. The main nitrate fertilizers are ammonium, sodium, potassium, several million kilograms are produced annually for this purpose. The second major application of nitrates is as oxidizing agents, most notably in explosives where the oxidation of carbon compounds liberates large volumes of gases. Sodium nitrate is used to air bubbles from molten glass. Mixtures of the salt are used to harden some metals. Explosives and table tennis balls are made from celluloid, although nitrites are the nitrogen compound chiefly used in meat curing, nitrates are used in certain specialty curing processes where a long release of nitrite from parent nitrate stores is needed
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Nitrogen
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Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772, although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. Nitrogen is the lightest member of group 15 of the periodic table, the name comes from the Greek πνίγειν to choke, directly referencing nitrogens asphyxiating properties. It is an element in the universe, estimated at about seventh in total abundance in the Milky Way. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2, dinitrogen forms about 78% of Earths atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids, in the nucleic acids, the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, many industrially important compounds, such as ammonia, nitric acid, organic nitrates, and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen, the second strongest bond in any diatomic molecule. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric, Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many notable nitrogen-containing drugs, such as the caffeine and morphine or the synthetic amphetamines. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages, alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air. Though he did not recognise it as a different chemical substance, he clearly distinguished it from Joseph Blacks fixed air. The fact that there was a component of air that does not support combustion was clear to Rutherford, Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as air or azote, from the Greek word άζωτικός. In an atmosphere of nitrogen, animals died and flames were extinguished
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Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
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Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
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Agriculture
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Agriculture is the cultivation and breeding of animals, plants and fungi for food, fiber, biofuel, medicinal plants and other products used to sustain and enhance human life. Agriculture was the key development in the rise of human civilization. The study of agriculture is known as agricultural science, the history of agriculture dates back thousands of years, and its development has been driven and defined by greatly different climates, cultures, and technologies. Industrial agriculture based on large-scale monoculture farming has become the dominant agricultural methodology, genetically modified organisms are an increasing component of agriculture, although they are banned in several countries. Agricultural food production and water management are increasingly becoming global issues that are fostering debate on a number of fronts, the major agricultural products can be broadly grouped into foods, fibers, fuels, and raw materials. Specific foods include cereals, vegetables, fruits, oils, meats, fibers include cotton, wool, hemp, silk and flax. Raw materials include lumber and bamboo, other useful materials are also produced by plants, such as resins, dyes, drugs, perfumes, biofuels and ornamental products such as cut flowers and nursery plants. The word agriculture is a late Middle English adaptation of Latin agricultūra, from ager, field, Agriculture usually refers to human activities, although it is also observed in certain species of ant, termite and ambrosia beetle. To practice agriculture means to use resources to produce commodities which maintain life, including food, fiber, forest products, horticultural crops. This definition includes arable farming or agronomy, and horticulture, all terms for the growing of plants, even then, it is acknowledged that there is a large amount of knowledge transfer and overlap between silviculture and agriculture. In traditional farming, the two are often combined even on small landholdings, leading to the term agroforestry, Agriculture began independently in different parts of the globe, and included a diverse range of taxa. At least 11 separate regions of the Old and New World were involved as independent centers of origin, wild grains were collected and eaten from at least 105,000 years ago. Pigs were domesticated in Mesopotamia around 15,000 years ago, rice was domesticated in China between 13,500 and 8,200 years ago, followed by mung, soy and azuki beans. Sheep were domesticated in Mesopotamia between 13,000 and 11,000 years ago. From around 11,500 years ago, the eight Neolithic founder crops, emmer and einkorn wheat, hulled barley, peas, lentils, bitter vetch, chick peas and flax were cultivated in the Levant. Cattle were domesticated from the aurochs in the areas of modern Turkey. In the Andes of South America, the potato was domesticated between 10,000 and 7,000 years ago, along with beans, coca, llamas, alpacas, sugarcane and some root vegetables were domesticated in New Guinea around 9,000 years ago. Sorghum was domesticated in the Sahel region of Africa by 7,000 years ago, cotton was domesticated in Peru by 5,600 years ago, and was independently domesticated in Eurasia at an unknown time
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Fertilizer
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A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soils or to plant tissues to supply one or more plant nutrients essential to the growth of plants. Fertilizers enhance the growth of plants and this goal is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration and this article, like many on fertilizers, emphasises the nutritional aspect. The nutrients required for plant life are classified according to the elements. Instead compounds containing these elements are the basis of fertilizers, the macronutrients are consumed in larger quantities and are present in plant tissue in quantities from 0. 15% to 6. 0% on a dry matter basis. Plants are made up of four elements, hydrogen, oxygen, carbon. Carbon, hydrogen and oxygen are widely available as water and carbon dioxide, although nitrogen makes up most of the atmosphere, it is in a form that is unavailable to plants. Nitrogen is the most important fertilizer since nitrogen is present in proteins, DNA, to be nutritious to plants, nitrogen must be made available in a fixed form. Only some bacteria and their host plants can fix atmospheric nitrogen by converting it to ammonia, phosphate is required for the production of DNA and ATP, the main energy carrier in cells, as well as certain lipids. Micronutrients are consumed in quantities and are present in plant tissue on the order of parts-per-million, ranging from 0.15 to 400 ppm DM. These elements are present at the active sites of enzymes that carry out the plants metabolism. Because these elements enable catalysts their impact far exceeds their weight percentage, Fertilizers are classified in several ways. They are classified according to whether they provide a single nutrient, multinutrient fertilizers provide two or more nutrients, for example N and P. Fertilizers are also sometimes classified as inorganic versus organic. Inorganic fertilizers exclude carbon-containing materials except ureas, organic fertilizers are usually plant- or animal-derived matter. Inorganic are sometimes called synthetic fertilizers since various chemical treatments are required for their manufacture, the main nitrogen-based straight fertilizer is ammonia or its solutions. Ammonium nitrate is widely used. Urea is another source of nitrogen, having the advantage that it is solid and non-explosive, unlike ammonia and ammonium nitrate. A few percent of the fertilizer market has been met by calcium ammonium nitrate
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Explosive material
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An explosive charge is a measured quantity of explosive material, which may be composed of a single ingredient or a combination of two or more. Materials that detonate are said to be high explosives and materials that deflagrate are said to be low explosives, Explosives may also be categorized by their sensitivity. Sensitive materials that can be initiated by a small amount of heat or pressure are primary explosives. A wide variety of chemicals can explode, a number are manufactured specifically for the purpose of being used as explosives. The remainder are too dangerous, sensitive, toxic, expensive, unstable, in contrast, some materials are merely combustible or flammable if they burn without exploding. The distinction, however, is not razor-sharp, though early thermal weapons, such as Greek fire, have existed since ancient times, the first widely used explosive in warfare and mining was black powder, invented in 9th century China. This material was sensitive to water, and it produced copious amounts of dark smoke, the first useful explosive stronger than black powder was nitroglycerin, developed in 1847. Since nitroglycerin is a liquid and highly unstable, it was replaced by nitrocellulose, TNT in 1863, smokeless powder, dynamite in 1867, World War I saw the adoption of TNT trinitrotoluene in artillery shells. World War II saw a use of new explosives. In turn, these have largely replaced by more powerful explosives such as C-4. However, C-4 and PETN react with metal and catch fire easily, yet unlike TNT, C-4 and PETN are waterproof, the largest commercial application of explosives is mining. In Materials Science and Engineering, explosives are used in cladding, a thin plate of some material is placed atop a thick layer of a different material, both layers typically of metal. Atop the thin layer is placed an explosive, at one end of the layer of explosive, the explosion is initiated. The two metallic layers are forced together at high speed and with great force, the explosion spreads from the initiation site throughout the explosive. Ideally, this produces a metallurgical bond between the two layers and it is possible that some fraction of the surface material from either layer eventually gets ejected when the end of material is reached. Hence, the mass of the now welded bilayer, may be less than the sum of the masses of the two initial layers, there are applications where a shock wave, and electrostatics, can result in high velocity projectiles. Thus, explosives are substances that contain an amount of energy stored in chemical bonds. Consequently, most commercial explosives are compounds containing -NO2, -ONO2 and -NHNO2 groups that
30.
ANFO
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ANFO is a widely used bulk industrial explosive. It consists of 94% porous prilled ammonium nitrate, which acts as the agent and absorbent for the fuel. ANFO is also used in avalanche hazard mitigation. It accounts for an estimated 80% of the 2. 7×109 kg of explosives used annually in North America, the press and other media have used the term ANFO loosely and imprecisely in describing IEDs, in cases of fertilizer bombs. The use of ANFO originated in the 1950s, the chemistry of ANFO detonation is the reaction of ammonium nitrate with a long-chain alkane to form nitrogen, carbon dioxide, and water. In an ideal stoichiometrically balanced reaction, ANFO is composed of about 94. 3% AN and 5. 7% FO by weight, in practice, a slight excess of fuel oil is added, as underdosing results in reduced performance while overdosing merely results in more post-blast fumes. When detonation conditions are optimal, the gases are the only products. In practical use, such conditions are impossible to attain, and blasts produce moderate amounts of gases such as carbon monoxide. The fuel component of ANFO is typically diesel, but kerosene, coal dust, racing fuel, finely powdered aluminium in the mixture will sensitise it to detonate more readily. ANFO is classified as an explosive, meaning that it decomposes through detonation rather than deflagration at a velocity higher than the speed of sound in the material. ANFO has a moderate velocity compared to other explosives, measuring 3,200 m/s in 130 mm diameter, unconfined. ANFO is an explosive, meaning that it cannot be set off by the small quantity of primary explosive in a typical blasting cap. A larger quantity of explosive, known as a primer or a booster. One or two sticks of dynamite were used, current practice is to use Tovex or cast boosters of pentolite. In the mining industry, the term ANFO specifically describes a mixture of ammonium nitrate prills. Other explosives based on the ANFO chemistry exist, the most commonly used are emulsions and they differ from ANFO in the physical form the reactants take. The most notable properties of emulsions are water resistance and higher bulk density, while the density of pure crystalline ammonium nitrate is 1700 kg/m3, individual prills of explosive-grade AN measure approximately 1300 kg/m3. Their lower density is due to the presence of a spherical air pocket within each prill
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Improvised explosive device
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An improvised explosive device is a bomb constructed and deployed in ways other than in conventional military action. It may be constructed of conventional explosives, such as an artillery round. IEDs are commonly used as roadside bombs, IEDs are generally seen in heavy terrorist actions or in unconventional warfare by guerrillas or commando forces in a theater of operations. In the second Iraq War, IEDs were used extensively against US-led invasion forces and they are also used in Afghanistan by insurgent groups, and have caused over 66% of coalition casualties in the 2001–present Afghanistan War. IEDs were also used extensively by cadres of the rebel Tamil Tiger organization against military targets in Sri Lanka, an IED is a bomb fabricated in an improvised manner incorporating destructive, lethal, noxious, pyrotechnic, or incendiary chemicals and designed to destroy or incapacitate personnel or vehicles. In some cases, IEDs are used to distract, disrupt, or delay an opposing force, IEDs may incorporate military or commercially sourced explosives, and often combine both types, or they may otherwise be made with homemade explosives. An IED has five components, a switch, an initiator, container, charge, an IED designed for use against armoured targets such as personnel carriers or tanks will be designed for armour penetration, by using a shaped charge that creates an explosively formed penetrator. IEDs are extremely diverse in design and may contain many types of initiators, detonators, penetrators, antipersonnel IEDs typically also contain fragmentation-generating objects such as nails, ball bearings or even small rocks to cause wounds at greater distances than blast pressure alone could. IEDs are triggered by various methods, including remote control, infrared or magnetic triggers, in some cases, multiple IEDs are wired together in a daisy chain to attack a convoy of vehicles spread out along a roadway. IEDs made by inexperienced designers or with substandard materials may fail to detonate, the sophistication of an IED depends on the training of the designer and the tools and materials available. IEDs may use artillery shells or conventional high-explosive charges as their explosive load as well as homemade explosives, chlorine liquid has been added to IEDs in Iraq, producing clouds of chlorine gas. A vehicle-borne IED, or VBIED, is a term for a car bomb or truck bomb but can be any type of transportation such as a bicycle, motorcycle, donkey. They are typically employed by insurgents, and can carry a large payload. They can also be detonated from a remote location, vBIEDs can create additional shrapnel through the destruction of the vehicle itself and use vehicle fuel as an incendiary weapon. The act of a persons being in this vehicle and detonating it is known as an SVBIED suicide, the fougasse was improvised for centuries, eventually inspiring factory-made land mines. Ernst Jünger mentions in his war memoir the systematic use of IEDs, another early example of coordinated large-scale use of IEDs was the Belarusian Rail War launched by Belarusian guerrillas against the Germans during World War II. Both command-detonated and delayed-fuse IEDs were used to derail thousands of German trains during 1943–1944, starting six months before the invasion of Afghanistan by the USSR on 27 December 1979, the Afghan Mujahideen were supplied with large quantities of military supplies. Among those supplies were many types of anti-tank mines, the insurgents often removed the explosives from several foreign anti-tank mines, and combined the explosives in tin cooking-oil cans for a more powerful blast
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