Ionic Crystlas
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Crystals have varied structures, shapes, and characteristics the focus of this paper would be ionic crystals. It will also include the uses of these crystals and the formation of ionic crystals. Ionic crystals have different systems such as, isometric or cubic, hexagonal, tetragonal, orthormbic, monoclinic, and triclinic. In order for one to understand crystals one must define the object. In chemistry, a crystal is a solid which constituents atoms, molecules or ions packed in a regular order, repeating pattern extending in all three spatial directions.
Crystals are formed through a process called solidification. The result of this process can either be a single crystal in which atoms in a solid fit into the same crystal structure. Crystallization is the process in which ambient pressure allows crystalline structures to solidify. Another fact is the way crystals can form simultaneously during solidification which leads to a polycrystalline solid (Wikipedia).Crystals can form when water evaporates; for example, salt crystals (sodium chloride) form when salt water evaporates(Ask a Scientist). Another ideal method in which crystals form is nucleation unassisted nucleation or assisted nucleation (Kiwi Web).This depends on the internal symmetry of the crystal, the relative growth rates along the various directions in the crystal. If there is a highly attractive interaction along a certain direction of a crystal, then that direction will probably grow fast (FAQ on Crystals). A crystals structure is generally repeated in three dimensions on a lattice in which an infinite set of discrete translation operations. The symmetry properties of a crystal are embodied in its space group. A crystal structure and symmetry play role in determining their property, such as cleavage, electronic band structure, and optical properties (Wikipedia) .The shape of these crystals is dependent on the types of molecular bonds between the atoms to determine the structure as well as the conditions under which they form (Wikipedia). A few examples of crystals are snowflakes, diamonds, and common salt. Another characteristic of crystal is the fact that light can pass through a crystal and can often retract or bend in different directions, producing array of colors (Umland 452).There are 14 different bravais lattices which are used to determine the geometric arrangement at lattice points and translational symmetry of a crystal (Wikipedia). Normally, ionic crystals consist of ions bound together by their electrostatic attraction. Examples of these occurrences are found in alkali halides, with different combinations of sodium, cesium, rubidium or lithium ions with fluoride, bromide, chloride or iodide ions. The exact arrangement of ions in an ionic lattice varies according to the size of the ions in the solid. They are also characterized by a strong absorption of infrared with planes that cleave easily (Wikipedia). These crystals have at least two atoms in their base which are ionized. Charge neutrality demands that a total charge in the base must be zero; so they always need ions with opposing charges. Ionic crystals occupy minimum volume and electrostatic energy. It is important that ionic crystals are insulators (Ionic Crystals). Ionic crystals are ideally classified as crystals that have binding which is not exclusively ionic but includes a certain admixture of covalent binding. Ionic crystals exhibit characteristics of more than one crystal type. Due to the fact they are generally good electronic insulators they have large band gaps (Answers.com).
There are seven unique crystal systems. The simplest is the cubic system which has three axes that are perpendicular and of equal length. The other six systems fall in descending order of symmetry which is hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, and triclinic. There are 14 unique Bravais lattices which used to determine the geometric arrangement at lattice point, and thereby translational symmetry of the crystal (Wikipedia). The crystallographic point group or crystal class is the set of non-translational symmetry of operations that leave the appearance of the crystal structure unchanged. The symmetry operation deals with the mirror plane, which rotates the structure a specified number of degrees, and center of symmetry (Wikipedia). The space group of the crystal structure is composed of the translational symmetry operations in addition to the operations of the point group. Pure translations move a point along a vector, screw axes, which rotate a point around an axis while translating parallel to the axis. The glide planes, which reflect a point through a plane while translating it parallel to the plane. There are 230 distinct space groups (Answers.com).
Simple cubic crystals have the easiest arrangement of identical spheres. The structure of a simple cubic are layers stacked with atoms of one layer directly on top of the atoms of the other layers(Umland, 456) .The simple cubic system consists of one lattice point on each corner of the cube. Each lattice point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one lattice point. The body centered cubic system has one lattice point in the center of the unit cell in addition to the eight corner points. It has in total 2 lattices points per cell.
Finally, the face centered cubic lattice has lattice points on the faces of the cube, giving a total of 4 lattice points. There are 36 cubic space groups (Wikipedia).
Orthorhombic crystal systems are one of the lattice point groups which represent the field of dots. A whole crystal lattice could be described by the lattice points and the motif called the unit cell. Unit cells may contain more than one lattice point. Orthorhombic lattice is the result of the stretching of the cubic lattice along two of its vectors by two different factors resulting in a rectangular prism with a rectangular base and height. All three vectors bases intersect at 900 angle (Crystal Systems).The three lattice vectors remain mutually perpendicular. There are four orthorhombic Bravais lattices: simple orthorhombic, base-centered orthorhombic, body-centered orthorhombic and face-centered orthorhombic. The lattice centering corresponds with each beginning with simple orthorhombic which is the primitive centering where the lattice points are on the corners of the cell. Body-centered orthorhombic is one additional lattice point at the center of the cell. Face-Centered which deals with the one additional lattice point at the center of each of the faces of the cell. Base Centered Orthorhombic is on a single face such as with one additional lattice point at the center of each face of the cell. Among the orthorhombic system there are two groups bipyramidal, pyramidal, and sphenodial. An example of each group is sulfur, hemimorphite, and eposmite (Wikipedia). In the