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=== Article of the Week <font size=1>[ [[CZ:Article of the Week|about]] ]</font> ===
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=== Draft article of the Week <font size=1>[ [[CZ:Article of the Week|about]] ]</font> ===
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'''[[Lead]]''' is a [[chemical element]]. It is a [[heavy metal]], and is abundant in nature.  Lead has the symbol Pb (from the Latin Plumbum).  Its [[atomic number]] is 82. Lead is a very corrosion-resistant, dense, ductile, and malleable blue-gray metal that has been used for at least 5,000 years.
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[[Image:Liquid_water_simulation.jpg|thumb|right|200px|Snapshot from a simulation of liquid water. The four thin green lines from the molecule in the center of the picture represent hydrogen bonds.]]
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In [[chemistry]], a '''hydrogen bond''' is a type of attractive [[intermolecular force]] that exists between two [[partial charge|partial]] [[electric charge]]s of opposite polarity. Although stronger than most other [[intermolecular force]]s, the typical hydrogen bond is much weaker than both the [[ionic bond]] and the [[covalent bond]]. Within [[macromolecule]]s such as [[protein]]s and [[nucleic acid]]s, it can exist between two parts of the same molecule, and figures as an important constraint on such molecules' overall shape.
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Early uses of lead included building materials, [[pigments]] for [[glazing]] [[ceramics]], and [[pipe]]s for transporting water. Prior to the early [[1900's]], uses of lead were primarily for [[ammunition]], [[brass]], burial vault liners, ceramic glazes, [[leaded glass]] and [[crystal]], [[paint]]s or other protective coatings, [[pewter]], and water lines and pipes. The advent of the [[electricity|electrical age]] and [[Communications Age|communications]], which were accelerated by technological developments in [[World War I]], resulted in the addition of [[bearing metals]], cable covering, [[caulking]] lead, [[solder]]s, and type metal to the list of lead uses.  With the growth in production of [[Automobile|public and private motorized vehicles]] and the associated use of starting-lighting-ignition (SLI) [[lead-acid storage batteries]] and [[terne metal]] for gas tanks after World War I, demand for lead increasedLater, [[radiation shielding]] in [[Radiography|medical analysis]] and [[Television|video display equipment]] and as an [[Tetraethyl Lead|additive in gasoline]] also increased usage.
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As the name "hydrogen bond" implies, one part of the bond involves a [[hydrogen]] [[atom]]. The hydrogen atom must be attached to one of the elements [[oxygen]], [[nitrogen]] or [[fluorine]], all of which are strongly [[Electronegativity|electronegative]]
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<font size=1>[[Lead|['''more...''']]]</font>
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[[heteroatom]]s. These bonding elements are known as the hydrogen-bond ''donor''. This electronegative element attracts the electron cloud from around the hydrogen nucleus and, by decentralizing the cloud, leaves the atom with a positive partial charge. Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, nevertheless represents a large charge density. A hydrogen bond results when this strong positive charge density attracts a [[lone pair]] of electrons on another [[heteroatom]], which becomes the hydrogen-bond ''acceptor''.   
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<font size=1>[[Hydrogen bond|['''more...''']]]</font>

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Draft article of the Week [ about ]

Snapshot from a simulation of liquid water. The four thin green lines from the molecule in the center of the picture represent hydrogen bonds.

In chemistry, a hydrogen bond is a type of attractive intermolecular force that exists between two partial electric charges of opposite polarity. Although stronger than most other intermolecular forces, the typical hydrogen bond is much weaker than both the ionic bond and the covalent bond. Within macromolecules such as proteins and nucleic acids, it can exist between two parts of the same molecule, and figures as an important constraint on such molecules' overall shape.

As the name "hydrogen bond" implies, one part of the bond involves a hydrogen atom. The hydrogen atom must be attached to one of the elements oxygen, nitrogen or fluorine, all of which are strongly electronegative heteroatoms. These bonding elements are known as the hydrogen-bond donor. This electronegative element attracts the electron cloud from around the hydrogen nucleus and, by decentralizing the cloud, leaves the atom with a positive partial charge. Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, nevertheless represents a large charge density. A hydrogen bond results when this strong positive charge density attracts a lone pair of electrons on another heteroatom, which becomes the hydrogen-bond acceptor. [more...]


New Draft of the Week [ about ]

Although bound up with the tradition of the ‘special library’, information management differs from such earlier concepts in its focus on all kinds of information and a concern for the relationship between information provision and organizational performance. In many special libraries there had long been responsibility for managing internal documentation of various kinds, especially research reports. The history of this development is usefully explored by Black, Muddiman and Plant [1] who note the emergence of information management concepts following the end of the First World War, with the formal organization of ‘information bureaux’ in the establishment of ASLIB (the Association of Special Libraries and Information Bureaux) in the UK in 1924. Some techniques, however, were even older, witness Kaiser’s work on indexing [2][3]. Indeed, we can date many of the ideas of what is now called ‘information management’ (although ‘documentation’ is used as a near equivalent in much of Europe) to the founding by Otlet and La Fontaine of the International Institute of Bibliography in 1895 [more...]

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