Crystals Essay

1094 words - 5 pages

I. Introduction- What is a crystal?
A crystal by definition is a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern. These magnificent solids are formed when they undergo a process called nucleation. Nucleation is the process that occurs in the formation of a crystal. The solution’s, liquid’s, or vapor’s (whichever the crystal is growing in) ions, atoms, or molecules become arranged in a pattern which has the characteristics of a crystalline solid. This pattern forms the site the additional particles left will be deposited into as the crystal grows. A crystal’s structure consists of matter that is formed from an ordered arrangement of atoms, molecules, or ions. The structure consists of repeated units giving the structure recognizable features.
II. Lattice Systems and Chemical Properties
Crystal Structures are divided into seven systems called lattices. A lattice is the arrangement of points of the atoms, ions, or molecules composing a crystal are centered at. The seven systems crystals are divided into consist of Cubic, Tetragonal, Orthorhombic, Hexagonal, Trigonal, Triclinic, and Monoclinic. The Cubic system is fairly basic. It consists of one lattice point on each corner of the cube, which each lattice point shared equally between eight adjacent cubes. The Tetragonal system is similar to the cubic crystals, but it is longer along one axis. Tetragonal crystal lattices form when stretching has occurred along one lattice vector. As a result, the cube is turned into a rectangular prism with a square base. The Orthorhombic system is like the Tetragonal crystals, but it does not have a square in the cross section. This lattice is formed when stretching has occurred along two lattice vectors, which forms a rectangular prism with a rectangular base. The Hexagonal system consists of a six-sided prism. When the crystal is viewed on-end, the cross section is a hexagon. A hexagonal lattice has symmetry much like a right prism with a hexagonal base. Graphite is one example of a crystal with a hexagonal lattice. The Trigonal system is much like the Hexagonal system, but possesses a three-fold axis instead of a six-fold. The vectors of this crystal are all equal length. The Triclinic system is usually not symmetrical from side to side. The crystals usually have fairly strange shapes. The vectors of this crystal are of unequal length. The final system is the Monoclinic system. These crystals often form prisms and double pyramids. The vectors are of unequal length which forms a rectangular prism with a parallelogram as its base.
When grouping crystals by their chemical and physical properties, there are four main groups or categories. The groups include, Covalent Crystals, Metallic Crystals, Ionic Crystals, and Molecular Crystals. Covalent Crystals have a true covalent bond between the atoms of the crystal. Most of the covalent crystals have extremely high melting points. Examples of covalent crystals include diamond and...

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