A solid may be crystalline or amorphous
Crystalline solids :
A crystalline solid may be a mono crystal or poly crystal. A solid in which atoms, ions, or molecules are arranged in regular repeated three dimentional pattern in solid to be crystallin.
Amorphour solids :
Amorphous solids may be regarded as super cooled liquids. Many plastics, pith and glass are amorphous. Amorphous solids exhibit short range orders. In boron tri oxide for example :- each boron is surrounded by three oxygen atoms. This short range order is repeasted in a regular fashion and there is a long range order also. Thus boron tri oxide is crystalline. If it lacks this range of order it is called amorphous.
Crystalline lattice :
The x-ray diffraction on crystals show that the atoms or molecules in a crystal are arranged in a regular array of points. A regular periodic arrangements of arrangements of points in space is called lattice. In a cystal each lattice point has a group of atoms or ions attached to it such a group of atoms attached to a lattice point is called lattice. A lattice in a regular periodic arrangement looks like a net like structure. The environment about any particular point is in every way the same as that about any other part. The crystal structure is thus specified characterised by the type of the lattice associated with it. An ideal crystal is constructed by infinite repetitions in space and identical.
Structural units :
The structural of all the crystals is discribed in terms of a lattice with a group of atoms attached to each lattice point. The group is called the basis, it is repeated in space to form the crystal lattice.
Lattice + basis = Crystal structure.
One important condition is that an array of points has to satisfy certain conditions in order that it may be called a lattice. The environment of each point in the array must be the same. The position vectors of the immediate neighbours of every other point in the array is clearly the same. A crystal structure is formed by an addition of basis to every lattice point. The number of atoms in the basis may be as low as one or it may exceed 1000 atoms.
The lattice can be constructed by imagining simple translations of primitive cell. A primitive lattice cell is a type of cell or of unit cell. A cell will fill all the space by suitable crystal translational operations. A primitive cell is a minimum volume cell. The number of atoms in the primitive basis will be same. There is a density of one lattice per primitive cell. The volume of the cell is defined by axis a, b, c is Vc = | a x b.c| by elementary vector analysis no basis contains fewer atoms than a primitive basis. This is also called Wigxes - Seitz primitive cell.
A unit cell may be a square, a rectangular, a parallelogram or a hexagon. A unit cell may be such that while building up the lattice there should not be any uncovered areas or over lapping. Thus a pentagon or a heptogon cannot be a unit cell because it cannot cover wide area with out over lappings.
A two dimensional lattice can be considered to be made of two sets of parallel lines say x-y direction. The points of intersection are called lattice points. Taking one of the lattice points as origin any other lattice point p can be represented by the vector r, ma+nb. Here a is a unit vector along x direction and is equal to distance between tow consecutive points along x direction, b is a unit vector along y direction, m and n are two integers.
A three dimensional lattice can be constructed to be made of three sets of parallel lines along x,y,z directions intersecting each other at a point o. ox, oy, oz and the three axis along which a, b, c are the unit vectors represented. There are no restrictions on the lengths a, b, of the lattice translation vectors or on the angle between them. There fore there are unlimited possible number of lattice. A general lattice of obliquely is invaliant only under rotation..................................READ
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Crystalline solids :
A crystalline solid may be a mono crystal or poly crystal. A solid in which atoms, ions, or molecules are arranged in regular repeated three dimentional pattern in solid to be crystallin.
Amorphour solids :
Amorphous solids may be regarded as super cooled liquids. Many plastics, pith and glass are amorphous. Amorphous solids exhibit short range orders. In boron tri oxide for example :- each boron is surrounded by three oxygen atoms. This short range order is repeasted in a regular fashion and there is a long range order also. Thus boron tri oxide is crystalline. If it lacks this range of order it is called amorphous.
Crystalline lattice :
The x-ray diffraction on crystals show that the atoms or molecules in a crystal are arranged in a regular array of points. A regular periodic arrangements of arrangements of points in space is called lattice. In a cystal each lattice point has a group of atoms or ions attached to it such a group of atoms attached to a lattice point is called lattice. A lattice in a regular periodic arrangement looks like a net like structure. The environment about any particular point is in every way the same as that about any other part. The crystal structure is thus specified characterised by the type of the lattice associated with it. An ideal crystal is constructed by infinite repetitions in space and identical.
Structural units :
The structural of all the crystals is discribed in terms of a lattice with a group of atoms attached to each lattice point. The group is called the basis, it is repeated in space to form the crystal lattice.
Lattice + basis = Crystal structure.
One important condition is that an array of points has to satisfy certain conditions in order that it may be called a lattice. The environment of each point in the array must be the same. The position vectors of the immediate neighbours of every other point in the array is clearly the same. A crystal structure is formed by an addition of basis to every lattice point. The number of atoms in the basis may be as low as one or it may exceed 1000 atoms.
The lattice can be constructed by imagining simple translations of primitive cell. A primitive lattice cell is a type of cell or of unit cell. A cell will fill all the space by suitable crystal translational operations. A primitive cell is a minimum volume cell. The number of atoms in the primitive basis will be same. There is a density of one lattice per primitive cell. The volume of the cell is defined by axis a, b, c is Vc = | a x b.c| by elementary vector analysis no basis contains fewer atoms than a primitive basis. This is also called Wigxes - Seitz primitive cell.
A unit cell may be a square, a rectangular, a parallelogram or a hexagon. A unit cell may be such that while building up the lattice there should not be any uncovered areas or over lapping. Thus a pentagon or a heptogon cannot be a unit cell because it cannot cover wide area with out over lappings.
A two dimensional lattice can be considered to be made of two sets of parallel lines say x-y direction. The points of intersection are called lattice points. Taking one of the lattice points as origin any other lattice point p can be represented by the vector r, ma+nb. Here a is a unit vector along x direction and is equal to distance between tow consecutive points along x direction, b is a unit vector along y direction, m and n are two integers.
A three dimensional lattice can be constructed to be made of three sets of parallel lines along x,y,z directions intersecting each other at a point o. ox, oy, oz and the three axis along which a, b, c are the unit vectors represented. There are no restrictions on the lengths a, b, of the lattice translation vectors or on the angle between them. There fore there are unlimited possible number of lattice. A general lattice of obliquely is invaliant only under rotation..................................READ
Crystalline solids and Amorphous solids CLICK HERE
CLICK HERE to join this website for free
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