UNIT 1: SOLID STATE (Crystal Lattice & Unit Cell) CBSE XIITH CHEMISTRY KEY NOTES PART II

 

• Crystal Lattice: A 3D arrangement of points representing the periodic arrangement of atoms, ions, or molecules in a crystalline solid.

• Unit Cell: The smallest repeating structural unit of the crystal lattice which, when repeated in all 3 directions, generates the entire crystal.

• Lattice Parameters:
• a, b, c → edge lengths
• α, β, γ → interaxial angles

• Contribution of Atoms

• Corner Atom: shared by 8 unit cells → contribution = 1/8

• Face Atom: shared by 2 unit cells → contribution = 1/2

• Body Atom: not shared → contribution = 1

    Types of Unit Cells

      There are mainly three types of cubic unit cells:

Type	Structure	Atoms at Corners	Atoms at Faces	Atoms Inside	Total Atoms / Unit Cell
Simple Cubic (SC)	1 atom at each corner	8	0	0	1
Body-Centered Cubic (BCC)	1 atom at each corner + 1 in center	8	0	1	2
Face-Centered Cubic (FCC)	1 atom at each corner + 1 at each face	8	6	0	4