Crystal Lattice | Structure Energy Definition And Intermolecular Bonding
Atoms found in crystals that are arranged in a geometrical and unique manner is known as Crystal Lattice. This state of arrangement is not found in formless solids or gasses. Crystal Lattice is just a three dimensional network of straight lines and their points of intersection. This lattice controls the main properties in crystals like the optical transparency, cleavage and structure of electronic band. The points in a lattice are comprised of tiny boxes that are identical and called as the unit cells that is the smallest part of the crystal lattices and they fill up the space of the lattice.
Crystal lattices can be classified according to their shape and according to their properties, both chemical and physical properties. When they are classified according to shape there are seven types of crystal lattices.
- Cubic Lattice: The cubic shape of lattice is also known as the Isometric crystal lattice. As the name suggests it need not always be in the cubical shape. This is one of the simplest types of lattice structure. On each corner of the cube there is one lattice point and these points are shared between the other eight cubes adjacent to it. Some times lattice’s can be found with ten faces too in and it is known as the dodecahedrons.
- Tetragonal Lattice: The tetragonal lattice is very much similar to the cubic crystal lattice with certain minor differences. In the tetragonal crystal lattices the points are longer on one of the axis when compared to the others, thus converting the cube into a rectangular prism which has a square base. With this structure, double prisms and pyramids are formed.
- Hexagonal Lattice: The hexagonal crystal lattice is nothing but a six cornered prism. Its symmetry is similar to that of a right prism, except for the fact that this structure has a hexagonal base. A perfect example for a hexagonal crystal is graphite. The cross-section of graphite's crystal is a hexagon.
- Orthorhombic Lattice: The Orthorhombic structure crystal lattices are similar to the tetragonal lattices. The orthorhombic lattice too is obtained by stretching a cubic lattice on two axis's using two factors. This results in a prism which is rectangular with a rectangular base. The major difference between these two lies in the cross section. The cross section for an orthorhombic prism forms dipyramids or rhombic prisms and not a square.
- Monoclinic Lattice: The monoclinic lattice structure is formed when vectors of non-equal length come together to form a prism which is rectangular in form and has a base like a parallelogram. They are usually like tetragonal crystals but skewed.
- Trigonal Lattice: The Trigonal Lattice or also commonly known as the Rhomboderal lattice possesses a single three fold axis when compared to a six fold axis of the hexagonal structure. Their vectors are of equal lengths but these three vectors are mutually not orthogonal. The structure of this crystal would be similar to a cubic structure but one that is stretched along the body diagonally.
- Triclinic Lattice: The Triclinic lattice is a structure that is not symmetrical and offers some weird shapes. All the vectors are not of equal length and they are also mutually not orthogonal.
The crystal lattices can further be classified into primitive lattices and non primitive lattices. A primitive lattice is one where one unit cell has only one lattice point and a non primitive lattice is where one unit cell has more than one lattice point. Thus these two types of lattices when combined with the seven basic lattice structure offers what is known as 14 Bravais Lattices. Bravais Lattices is named after the famous scientists Auguste Bravais who conducted an intensive study on various lattice structures as early as 1850's.