UNIT 1 THE SOLID STATE
- Solids have definite mass, volume and shape. This is due to the fixed position of their constituent particles, short distances and strong interactions between them.
- In amorphous solids, the arrangement of constituent particles has only short range order and consequently they behave like super cooled liquids. They do not have sharp melting points and are isotropic in nature.
- In crystalline solids, there is long range order in the arrangement of their constituent particles. They have sharp melting points, are anisotropic in nature and their particles have characteristic shapes.
- Properties of crystalline solids depend upon the nature of interactions between their constituent particles. On this basis, they can be divided into four categories: molecular, ionic, metallic and covalent solids.
- The constituent particles in crystalline solids are arranged in a regular pattern which extends throughout the crystal. This arrangement is often depicted in the form of a three dimensional array of points which is called crystal lattice.
- Each lattice point gives the location of one particle in space. In all, fourteen different types of lattices are possible which are called Bravais lattices.
- Each lattice can be generated by repeating its small characteristics portion called unit cell. A unit cell is characterized by its edge lengths and three angles between these edges.
- Close-packing of particles result in two highly efficient lattices, hexagonal close-packed (hcp) and cubic close-packed (ccp). The latter is also called face-centred cube (fcc) lattice. In both of these packings 74% space is filled. The remaining space is present in the form of two types of voids- octahedral voids and tetrahedral voids.
- Other types of packing are not close packings and have less efficient packing of particles. While in body-centred cubic lattice (bcc) 68% space is filled. in simple cubic lattice only 52.4% space is filled.
- Solids are not perfect in structure. There are different types of imperfections or defects in them. Types of defects:
- Point defects
- Stoichiometric defects
- Impurity defects
- Non-stoichiometric defects
- Line defects
- Point defects
- Solids show many types of magnetic properties like:
- Para magnetism
- Diamagnetism
- Ferromagnetism
- Anti-ferromagnetism
- Ferrimagnetism