Crystalline Structures

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Robert Rooke, in 1665, was one of the first ones to establish relations between the form of a crystal and its crystalline structure. Structure, in ampler direction, means: Organization of the parts or the elements that form one all. In 1784, Ren Hay, gave a step beyond Hooke and considered that the crystals could be understood as a wrapping up of rombodricas units that it called of ' ' molecules integrantes' '. A crystal currently is defined as a solid with its atoms arranged in three-dimensional periodic reticulado. The arrangement most steady apreesenta the following characteristics: – It groups atoms more compactly possible. – The electric neutrality Preserves. – The character directional of the covalentes linkings Satisfies.

– It minimizes repulses between ons. With the diverse studies concerning the relation between the crystalline structures and solids, it allows to say that the structure of the majority of solids is crystalline. However nor all the solids are crystalline. The glasses and the resins termorgidas, for example, are amorphous. The liquid crystals, that are nothing more than, little thick liquids also exist that present long molecules and that can be lined up parallel as in a crystal. The elastic constants, constant optics, electric condutividade, thermal condutividade, thermal dilatao and even though the chemical reactivity, depend on the crystalline orientation of the material. Moritz Frankenheim, was the first one to develop a systematic work describing and enumerating the space reticulados ones, however, it errneamente counted 15 reticulados space ones. Auguste Bravais, mathematician and French professor of physics, showed that Frankenheim counted two reticulados cristalograficamente equivalents doubly.

Space reticulado is an infinite, three-dimensional arrangement, points and in which all point has the same neighborhood and if calls reticulado point. As Bravais the points of the reticulado one can be associates in 14 different ways, involving 7 called systems Systems of Bravais, they are: – Cubical System: Simple, of Centered Body, Centered Faces. – Tetragonal System: Simple, of Centered Body. – Ortorrmbico System: Simple, of Centered Body, Centered Base, Centered Faces. – Rombodrico- System Hexagonal- System System Monoclnico: Simple, of Centered Base. – TriclnicoVrios elements presents in the solid state different crystalline structures. The denomination for that is allotropy. When the solid is a composed substance, the habitually used denomination is polimorfismo. These changes of structures generally occur in function of variations of temperature and pressure. The study of the crystalline structures and the knowledge of the characteristics of the reticulados ones of Bravais they allow to the planning and the understanding of the properties that certain materials have or will have. The study of the crystalline structures it is part of the Science of the Substances.

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