Crystal creating and To know how crystals are binding in periodic arrangement

Crystal binding

Crystalline material can be classified in many ways. For example, crystals can be classified according to their mechanical properties. etc. The most convenient basis for the classification of crystal is the character of the inter-atomic binding force in various types of crystalline materials.

    The atoms of a solid are bound together. This is called crystal binding we consider all types of matter in the solid form. For example, we consider even gases in the solid form and treat them as crystals. The binding of the atoms is due to the mutual attraction between the atoms. 

However a solid has very low compressibility which means it is very difficult to compress a solid and decrease its volume. We conclude that the atoms after crossing an equilibrium configuration, if brought still closer will try to repel each other. Therefore in the atomic scale, the attraction exists only at a distance greater than the critical distance. When we bring the atoms closer the critical distance is only repulsion. 

        When two atoms are brought closer there is a repulsive interaction coming into play in addition to the attractive interaction. This repulsive interaction is due to the electronic charge overlapping of the atoms and Pauli’s exclusion principle when the two charge distributions are just separated and repulsion.

       Pauli’s principle states that the two electrons in an atom cannot have all the quantum numbers alike. At least one quantum number should be different. When the charge distributions overlap, the outermost orbits of the two atoms also overlap. Thus there is a tendency for the two electrons having like spins to occupy the same orbit. 

This is impossible. Therefore the electrons in the first orbit are excited to the higher state and the overlapping electron occupies its position therefore the total energy of the system increases. We know that the attraction decreases the energy and therefore the tendency for an increase of energy will produce repulsion.

Periodic arrays of atoms

A crystal is identified by two properties namely periodicity and symmetry. These two properties give the crystal a regular shape. Periodicity means the repetition of atoms at regular intervals. Symmetry means that the configuration remains indistinguishable after an operation like translation rotation or reflection is performed.

  In actual crystals, either an atom or a group of atoms is repeated in space. The group of atoms is called the basic in the theoretical study of crystal structure; the basis is replaced by points. Which means the entire crystal is replaced by an imaginary array of points. Such a theoretical arrangement is called a space lattice.

 The actual crystal structure is obtained by replacing the lattice points with the basis. In the lattice, the points are shown separately. But in the actual crystal structure, the atoms are jam-packed. The space lattice is a regular periodic array of points in space. The crystal structure is formed when a basis of atoms is attached identically to every lattice point.