STATES OF MATTER-III-SOLIDS
KEY POINTS:
1. Amorphous solids:
Those solids in which the structural units i.e. atoms, ions, or molecules are fixed in their position but are not regularly arranged.
2. Anisotropy:
It is the variation of a certain physical property with a change in direction.
3. Covalent crystals:
Those crystals in which the non-metallic atoms are held together in a network of single covalent bonds.
4. Crystal lattice or space lattice:
A particular three-dimensional arrangement of particles i.e. atoms, ions, or molecules in a crystal is called a crystal lattice or space lattice.
5. Crystal:
A three-dimensional shape bounded by plane surfaces that intersect at definite angles with each other.
6. Lattice crystals:
Those crystals in which the oppositely charged ions are held together by an ionic bond.
7. Metallic crystals:
Those crystals in which the metal atoms are held together by metallic bonds.
8. Molecular crystals:
Those crystals in which the molecules are held together by Van der Waal's forces.
9. Unit Cell:
The smallest unit which when repeated in three dimensions can generate the structure of the entire crystal.