Class 12th "SOLID STATE"
A. Primitive Unit Cells/Simple Unit Cells(PC/SC) : When constituent particles are present only on the corner positions of a Unit cell, it is called a simple.
Example : Cubic, Tetragonal, Orthorhombic, Monoclinic, Triclinic, Hexagonal, Rhombohedral or Trigonal.
Calculation :
• Effective number of atoms per unit cell
• Contribution of an atom in the unit cell = (1/8)th of atom.
So,
Formula : {Effective no. of atoms = Corners of cubic×contribution of an atoms in one unit cell}
8×1/8 = 1 answer.
B. Body-Centred Cubic(BCC) : Such a unit Cells contains one constituent particles (atom, molecule, ion) at its body centre besides the ones that are it's corners.
Example : Cubic, Tetragonal, Orthorhombic.
Calculation :
• Effective no. of atoms per unit cell :
In BCC 8 atoms at 8 corners contributes = 8×1/8
= 1
One atom at the body centre = 1×1 = 1
EAN = 1+1
= 2 answer
C. Face-Centred Cubic(FCC) : Such a unit cell contains one constituent particles present at the centre of each face besides the ones that are at its corners.
Example : Cubic, Orthorhombic.
Calculation :
• Effective no. of atoms per unit cell (EAN)
• In an atom lies at the FCC it contribute 1/2 ( half) to the unit cell.
So, we have 8 atoms at the corners = 8×1/8 = 1
• six atoms at the faces = 6×1/2 = 3
• Total no.of atoms (EAN) = 1+3 = 4 answer.
D. End-Centred Cubic(ECC) : Such a unit cell contains one constituent particles present at the centre of any two opposite faces besides the ones present at its corners.
Example : Orthorhombic, Monoclinic.
• EAN = 6 answer.
THANK YOU !
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