Each oxygen atom (white sphere) is joined with four other oxygen atoms through covalent bonds with hydrogen atoms (black spheres). (a) Hexagonal symmetry and tetrahedral structures of the ice crystal lattice. In the solid phase, ice crystals form from individual water molecules bonded in symmetric, hexagonal plate structures (figure 2.1).Ī number of different ice-crystal structures have been experimentally identified, but hexagonal ice (Jh) is the only structure that forms at the range of temperatures material properties of snow and iœ b.įigure 2.1. The strong repulsion between the electron pairs distorts this, producing a lower bond angle of 104.5° in the liquid or vapor phase and giving water molecules a "bent" shape.
Water molecules group in a tetrahedral form, which should produce bond angles of 109.5°. The resulting intermolecular hydrogen bonds are even stronger as a result of water's small molecular size, which allows close packing. This dipolar nature creates strong intermolecular bonds between water molecules, as hydrogen atoms are attracted to the electron pairs of adjacent molecules. This structure gives water molecules a strong polarity, with a positive charge on the side with the hydrogen atoms and a negative charge opposite to this, associated with the electron pairs. Two electron pairs sit on the other side of the oxygen. The hydrogen atoms are grouped together on one side of the oxygen atom with a bond angle of 104.5°. Hydrogen atoms within a water molecule are held to the oxygen atom by strong covalent bonds. Also included on the site are updates of bug fixes, conditions of use and prices, tips for displaying the structures, a gallery of images, a flash movie, and instructions for installing a ICSD server.Water-familiar, household H20-has a simple molecular arrangement, but this simplicity and familiarity disguise the fact that water is a rather peculiar substance. The demo version can be queried and accessed by a web-interface which allows multiple methods of searching, and the resulting crystal structures can then be viewed online (with the CHIME plug-in) or downloaded for viewing with other visualization software. This database contains a 3325 structure subset of the 76,480 inorganic structures as of 2004.
CRYSTAL LATTICE STRUCTURE FREE
This site contains a free demonstration version of the Inorganic Crystal Structure Database. ICSD Web: the Inorganic Crystal Structure Database.Crystal structure data are downloadable in CIF format, and users may upload crystal data as CIF or REF files. The database is searchable by text, words, elements, volume, or number of elements. This database is a sister to the American Mineralogist Crystal Structure Database (AMCSD) and contains all the data that is in the AMCSD as well as data that has been deposited by individuals and laboratories. The crystal structure information includes mineral name, specification, crystal chemical formula, space group, unit cell parameters, coordinates, thermal factors and occupancy of atomic positions as well as literature references on crystal structure determination. Each mineral can be searched by name, specification, crystal chemical formula, or crystal structure characteristics. This searchable database, maintained by the Russian Foundation of Basic Research, includes 4785 entries (2365 unique mineral names). Crystallographic Database for Minerals and Their Structural Analogues.The site also includes links to other webpages about crystal structures. The Java applet allows the user to rotate and change the size of the crystal. This website features interactive Java applets of a variety of crystal structures of minerals and non-minerals. Several different graphical representations, an interactive Java applet of the structure, and useful information about the lattices can be obtained by clicking on images of crystal structures. Naval Research Laboratory, offers a concise index of common crystal lattice structures, including those from minerals and non-minerals. The site is searchable by mineral, author, chemistry, or cell parameters and symmetry. The database is maintained under the care of the Mineralogical Society of America and the Mineralogical Association of Canada, and financed by the National Science Foundation. This site is an interface to a crystal structure database that includes every structure published in the American Mineralogist, the Canadian Mineralogist, and the European Journal of Mineralogy. American Mineralogist Crystal Structure Database.
CRYSTAL LATTICE STRUCTURE SOFTWARE
The following online resources contain files which can be downloaded for interactive viewing either from a stand-alone visualization software or viewed from the website as a Java applet.
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