Formation of Crystal and Crystal Systems
The crystals of the substance are obtained by cooling the liquid (or the melt) of the solution of that substance. The size of the crystal depends upon the rate of cooling. If cooling is carried out slowly, crystals of large size are obtained because the particles (ions, atoms or molecules) get sufficient time to arrange themselves in proper positions.
Atoms of molecules cluster
dissolved embryo
crystal
(If loosing units dissolves as embryo and if gaining unit grow as a crystals).
Bravais (1848) showed from geometrical considerations that there can be only 14 different ways in which similar points can be arranged. Thus, there can be only 14 different space lattices. These 14 types of lattices are known as Bravais Lattices. But on the other hand Bravais showed that there are only seven types of crystal systems.
Table: Bravais lattices corresponding to different crystal systems
Crystal system |
Space lattice |
Examples | ||||||
Cubic
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Simple: Lattice points at the eight corners of the unit cells. | Body centered: Points at the eight corners and at the body centred. |
Face centered:Points at the eight corners and at the six face centres.
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Tetragonal
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Simple: Points at the eight corners of the unit cell. | Body centered: Points at the eight corners and at the body centre | ![]() ![]() ![]() ![]() ![]() |
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Simple: Points at the eight corners of the unit cell. |
End centered: Also called side centered or base centered. Points at the eight corners and at two face centres opposite to each other.
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Body centered : Points at the eight corners and at the body centre |
Face centered:Points at the eight corners and at the six face centres.
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or Trigonal
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Simple: Points at the eight corners of the unit cell | ![]() ![]() |
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Simple: Points at the twelve corners of the unit cell out lined by thick line.
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or Points at the twelve corners of the hexagonal prism and at the centres of the two hexagonal faces. | ![]() ![]() ![]() |
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Simple: Points at the eight corners of the unit cell | End centered: Point at the eight corners and at two face centres opposite to the each other. |
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Simple: Points at the eight corners of the unit cell. |
etc. |