Crystals

Crystals are solids that have their atoms and molecules arranged in a regular repeating pattern.

Read about Amorphous solids

Isomorphous

Two or more substances or solid  can have the same crystal structure . These substances are called isomorphous.

Amorphous

A non-crystal substances are called Amorphous

Crystal lattice

The arrangement of molecules or ions in a crystal is called crystal lattice

Crystallization

This is the process of making a crystal from crystal substances mostly by cooling it down from high temperature to low temperature or during chemical reaction when such crystal solid form.

Example of crystal substance is sodium chloride crystal. Its crystal is made up of sodium ions and chloride ions arranged in the form of a cube . see figure above . other  shapes of crystal can be octahedral and prismatic shapes’ see figure 2 and 3

The ions are held together by electro static force of attraction because they are opposite charges.. Each  of the ions are surrounded by six ions of opposite charges. i.e. six chloride ions surround one sodium ion and six sodium ions surround one chloride ion. Hence strong force is exacted on the one chloride ion and the one sodium ion being surrounded by six opposite charge. This makes the movement of the ions to be difficult and the whole lattice is strong. Also because of this strong force on the ions , the melting point of crystal substances are generally  high. 

General characteristic  of a crystal substances

1. Definite  and high melting point
2. Definite shapes
3. They are homogenous in nature. I.e. crystal of the same substances has the same shape
4. There is no free movement of molecules or ions in crystal substance
5. They are usually soluble
6. Crystallization can easily be achieved i.e. the process of making a crystal
7. They can be hydrated or anhydrous.
8.  They retain their shape when heated until the melting point.

Read other topics in High School Physics