CBSE class 12 ncert chemistry download pdf: Free Chemistry chapter-1 'Solid state' fast track revesion notes.

CBSE class 12 Ncert chemistry download pdf: Free Chemistry chapter-1 'Solid state' fast track revesion notes.

Solid State

1. Existence of matter as solid, liquid or gas depends upon the net effect of intermolecular forces and thermal energy. Solid state have definite mass. volume and shape. They are incompressible, rigid and intermolecular forces are strong.

2. Solids can be classified into two categories, viz. crystalline and amorphous depending upon the arrangement of constituent particles.

3. Crystalline solids (or true solids) have long range order of arrangeme of constituent particles and are anisotropic in nature, i.e. Cu, Ag etc. They melt at a sharp and have characteristic temperature. They have a definite and characteristic enthalpy of fusion. On the basis of nature of intermolecular forces operating in them the crystalline solids have been classified into following four types :

    (i) Molecular solids Constituent particles are.       molecules which are bonded through dipole-         dipole interaction/van der Waals' forces. e.g.         solid NH3 CO2 etc.

(ii) Metallic solids Constituent particles are positively charged metal ions (kernels) surrounded by sea of free electrons. The oppositely charge kernels and electrons hold ions together and is called metallic-bond. e.g. Fe, Cu, Ag etc. 

(iii)Covalent or network solids Constituent particles are non-metal atoms bonded with each other through covalent bonds. e.g. diamond, silicon carbide (SiC), graphite etc.

(iv) Ionic solids Constituent particles are positively and negatively charged ions bonded through strong electrostatic or coloumbic forces. e.g. NaCl, MgO, ZnS etc.

4. Amorphous solids or pseudo solids (also called supercooled liquids) have short range order of arrangement of constituent particles and are isotropic in nature, e.g. glass, rubber, plastic.

They have a tendency to flow, though very slowly. Glass panes fixed to windows or doors of buildings are found to become thicker at the bottom because the glass flows down slowly and makes the bottom portion thicker.

5. Crystal lattice The geometrical form consisting only of a regular array of points in space is called a lattice or space lattice.

• The scaffolding is a space lattice on which two dimensional pattern has been developed by placing structural units on its set of points. The structural unit is called basis or motif.

• A crystal lattice (space lattice) is the pattern of points representing the locations of these motifs.

6. Unit cell is the smallest portion of a crystal lattice which repeated in different directions, generates the entire lattice.

7. Types of unit cells Based upon the parameters of the unit cells (e. lengths a b and c and the angles a, B and y). there are seven types of unit cells. These are called crystal systems because any crystalline solid must belong to any one of these unit cells.

8. There are fourteen lattices corresponding to seven crystal systems, known as Bravais lattices.

9.Seven primitive unit cells and their possible variation as centred unit cell:

10. Types of cubic unit cells and number of atoms per unit cell are tabulated below:

11. Constituent particles in a crystal lattice can be packed in following three steps:

(i) One dimension Simple close packing (or linear)(CN 2).

(ii) Two dimension Square close packing (scp)(C.N. 4) and hexagonal close packing (hcp)(C.N.6).

(iii) Three dimension From 3D scp layers or from 3 hcp layers. (C.N. 12).

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