States of matter

There are three states (or phases) of matter i.e. solids, liquids and gases. Sometimes plasma is also considered a fourth state of matter which is a highly ionizable gas.

1.Solids: It is a state of matter which has a three-dimensional regularity of structure, resulting from the proximity of the component atoms, ions or molecules and the strength of the forces between them . In this closely packed structure molecules vibrate about fixed positions, solids are incompressible and all its atoms are in a state of perpetual motion. True solids are crystalline. If a crystalline solid is heated, the kinetic energy increases. At the melting point the binding forces between the components break down and the solid becomes a liquid.

2.Crystalline Solids: It has a regular internal arrangement of atoms, ions or molecules. Crystalline materials need not necessarily exist as crystals, for example, all metals are crystalline although they are not usually seen as regular geometric crystals.

3.Amorphous Solids: Some liquids do not solidify on cooling into true solids. Internal structure of this solid is haphazard and thus these solids are shapeless or amorphous. Glass is a common example.

4.Liquids: In a liquid, atomic (or ionic or molecular) regularity of the solid is absent. There is a short range structural regularity extending over several molecular diameters. These bundles of ordered atoms, molecules or ions are free to wonder about, enabling liquids to have almost fixed volumes which adopt the shape of their containers.

5.Gases: It is a fluid of which volume is not fixed. There are very weak bonds between the molecules of a gas, so the molecules are free to move.

Solid, liquid and gas are converted into each other through the melting, boiling, condensation and solidifying processes. At melting point any change involves the loss or gain of a certain amount of heat and this heat is called latent heat. Some impure and non-crystalline substances like glass, butter, etc. do not have definite melting points.

Volume of substances expand upon melting and shrinks upon solidifying but water expands on freezing. An additional amount of heat energy called the heat of vapourization is required to turn a liquid, such as water at 1000 C into steam at that same temperature. Properties like boiling and melting depend on pressure. At less than normal pressure, melting and boiling points are generally lower. On increasing the pressure, the boiling point and melting point generally increase but melting point of water decreases on increasing of pressure.