A detail description of crystal structure as well as different kind of crystal structure such simple cubic , body centric cubic and face centric cubic.

1. CRYSTAL STRUCTURE
By : Anchit Acharya

2. CRYSTALLINE SOLID
• A crystalline solid is formed by regular repetition of it’s building blocks(atoms,
molecule) in three dimension.
• A crystalline solid has a fixed
• geometrical structure.
• For eg : salt(sodium chloride),
Diamond , Sodium nitrate.
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3. CRYSTAL STRUCTURE
• Crystal structure is the description of ordered arrangement of atoms , ions or
molecules in a crystalline solid.
• The structure of crystals can be described in terms of lattice, with a group
of atoms attached to every lattice point.
• Lattice: lattice is the periodic arrangement points in space.
• Basis: basis is the atom or group of atoms.

4. UNIT CELL
• The unit cell is defined as the smallest repeating unit having full symmetry of the
crystal structure.
• It’s geometry and atomic positions define the crystal structure.
• When a unit cell is repeated in three dimension it reproduces the lattice.

5. SIMPLE CUBIC
• In the simple cubic structure there is only one lattice point at each corner of the
cube-shaped unit cell.
• They mark the position of either a single atom, or the same group of atoms, which is
repeated across the lattice.
• Polonium, is the only element with a simple cubic crystal structure.
• The number of atoms in unit cell is 1.

6. BODY CENTERED CUBIC
• Body centered cubic cell has atoms at each corner of the cube and an atom
at the center of the structure.
• The number of atoms in unit cell is 2.
• Examples of metals with the bcc structure are alpha iron, tungsten, chromium,
and beta titanium

7. FACE CENTERED CUBIC
• Face-centered cubic unit cell structure consists of atoms arranged in a cube where
each corner of the cube has an atom with six additional full atoms positioned at the
center of each cube face.
• The atoms at each face of the unit cell are shared with adjacent unit cells; therefore,
each face atom represents half of an atom.
• The numbers of atom in unit cell is
(1/2 atoms x 6 faces) + (1/8 atoms x 8 corners) = 4 atoms.

8. Fig : simple cubic
Fig: Body centered cubic Fig: Face centered cubic

9. PACKING FRACTION
• Atomic packing fraction tells what percentage of object is made of atom vs empty
space.
• It is like volume density or an indication of how tightly packed the atoms are.
• To calculate the packing fraction we divide the volume occupied by atom by total
volume i.e.
APF = volume taken by atoms
total volume

10. This is just the volume of unit cell.
Assuming that all atom have the same size and are arranged in repeating crystal
lattice.
APF= (N atoms) x (V atom) / V unit cell.
Crystal Structure Atomic Packing Factor
Simple Cubic (SC) 52%
Body-Centered Cubic (BCC) 68%
Face-Centered Cubic (FCC) 74%

11. THANK YOU