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Question
Distinguish between:
A)Hexagonal and monoclinic unit cells
B)Face−centred & end−centred unit cells.
A)Hexagonal and monoclinic unit cells
B)Face−centred & end−centred unit cells.
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Solution
A) Unit cell
Unit cell is a portion of crystal lattice which on repetition leads to crystal structure. It has all the characteristics of crystal lattice. The unit cell is characterized by three distances along the three edges of the lattice and the angles between them.
Difference between Hexagonal and monoclinic unit cells
propertiesHexagonal unit cellMonoclinic unit cellNo.of 3-D lattices12Possible variationsPrimitive Primitive and end centered Edge lengthsa=b≠ca≠b≠c
propertiesHexagonal unit cellMonoclinic unit cellAxial anglesα=β=90∘,γ=120∘α=γ=90∘,β≠90∘ExamplesGraphite,ZnO,CdS Na2SO4.10H2O,Monoclinic sulphur
B)Unit cell
Unit cell is a portion of crystal lattice which on repetition leads to crystal structure. It has all the characteristics of crystal lattice. The unit cell is characterized by three distances along the three edges of the lattice and the angles between them.
Difference between Face-centred and End-centred unit cells
propertiesFace centred unit cellEnd centred unit cellLocation of constituent particlesIt contains one constituent particle present at the centre of each face, besides the ones present at its corners It contains one constituent particle present at the centre of any two opposite faces, besides the ones present at its corners.
propertiesFace centred unit cellEnd centred unit cellNumber of constituent particlesA face centred unit cell has 4 atoms per unit cell.An end centred unit cell has 2 atoms per unit cell. Possible variationsFace centred unit cell is present in cubic and orthorhombic crystal systems.End centred unit cell is present in orthorhombic and monoclinic crystal
propertiesFace centred unit cellEnd centred unit cellExamplesCu,Al,Pt,Au~and BaSO4MgSO4.7H2O~and Na2SO4.10H2O
Unit cell is a portion of crystal lattice which on repetition leads to crystal structure. It has all the characteristics of crystal lattice. The unit cell is characterized by three distances along the three edges of the lattice and the angles between them.
Difference between Hexagonal and monoclinic unit cells
propertiesHexagonal unit cellMonoclinic unit cellNo.of 3-D lattices12Possible variationsPrimitive Primitive and end centered Edge lengthsa=b≠ca≠b≠c
propertiesHexagonal unit cellMonoclinic unit cellAxial anglesα=β=90∘,γ=120∘α=γ=90∘,β≠90∘ExamplesGraphite,ZnO,CdS Na2SO4.10H2O,Monoclinic sulphur
B)Unit cell
Unit cell is a portion of crystal lattice which on repetition leads to crystal structure. It has all the characteristics of crystal lattice. The unit cell is characterized by three distances along the three edges of the lattice and the angles between them.
Difference between Face-centred and End-centred unit cells
propertiesFace centred unit cellEnd centred unit cellLocation of constituent particlesIt contains one constituent particle present at the centre of each face, besides the ones present at its corners It contains one constituent particle present at the centre of any two opposite faces, besides the ones present at its corners.
propertiesFace centred unit cellEnd centred unit cellNumber of constituent particlesA face centred unit cell has 4 atoms per unit cell.An end centred unit cell has 2 atoms per unit cell. Possible variationsFace centred unit cell is present in cubic and orthorhombic crystal systems.End centred unit cell is present in orthorhombic and monoclinic crystal
propertiesFace centred unit cellEnd centred unit cellExamplesCu,Al,Pt,Au~and BaSO4MgSO4.7H2O~and Na2SO4.10H2O
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