晶体,crystal概要1.pptVIP

In addition, macroscopic?single crystals?are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations. * CONTENTS 1. Definition 2.Crystal structure (microscopic) 3. Crystal faces and shapes 4.Chemical bonds 5. Gallery Definition A?crystal?is a?solid?material whose constituents, such as?atoms,?molecules?or ions, are arranged in a highly ordered microscopic structure, forming a?crystal lattice?that extends in all directions. Crystal structure (microscopic) Microscopic structure of a halite crystal. Macroscopic (~16cm) halite crystal. A crystal is a solid where the atoms form a periodic arrangement. A crystal structure is characterized by its unit cell. There are 219 possible crystal symmetries, called crystallographic space groups. These are grouped into 7 crystal systems, such as cubic crystal system or hexagonal crystal system. Crystal faces and shapes As a halite crystal is growing, new atoms can very easily attach to the parts of the surface with rough atomic structure and many dangling bonds. Therefore these parts of the crystal grow out very quickly (yellow arrows). Eventually, the whole surface consists of smooth, stable faces, where new atoms cannot as easily attach themselves. Chemical bonds Ionically bonded crystals Covalently bonded crystals Weak van der Waals forces Hoar frost: A type of ice crystal (picture taken from a distance of about 5 cm). Gallium :a metal that easily forms large crystals. An apatite crystal sits front and center on cherry-red rhodochrosite rhombs, purple fluorite cubes, quartz and a dusting of brass-yellow pyrite cubes. Boules?of?silicon, like this one, are an important type of industrially-produced?single crystal. In addition, macroscopic?single crystals?are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations. *