CHEMISTRY CLASS 12, Chapter 1 Solid States Class 12 Chemistry, Chapter 1 Solid States | Page 14

A unit cell is characterized by:
( i) Its dimensions along the three edges, a, b and c which may or may not be mutually perpendicular.
o
Angles between the edges, α( between b and c) β( between and c) and γ( between a and b). Thus, a unit cell is characterized by six parameters a, b, c, α, β and γ.
Primitive Unit Cells
If the constituent particles of a crystal lattice are present only on the corner positions of a unit cell, it is known as primitive unit cell.
Centred Unit Cells
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If the constituent particles of a crystal lattice are present at positions other than corners in addition to those at corners, it is known as centred unit cell.
o Centered unit cells are of three types: o Body-Centred Unit Cells: