 |
| States of Matter
|
|
| All matter consists of atoms and molecules. Each of these atoms and molecules has certain amount of energy. The level of this energy decides the state in which the matter exists. When heat energy is supplied to matter, this energy level rises. As a result of this, state or the form in which a matter exists can change.
|
|
|
| Matter is classified into different categories depending upon its physical or chemical nature.
|
|
|
|
| Physically, matter can exist in three states or forms. These states are: Solid, Liquid and Gas. Atoms or molecules in the solid state have the least energy whereas those in the gaseous state have the maximum energy. In the case of liquids, the atoms or molecules have a midway energy. The basic differences between the three states of matter explained on the basis of dynamic particle model are as follows:
|
|
|
| Solid State
|
| In solids, atoms or molecules are closely packed and the intermolecular space or void is minimum. The average distance between particles is of the order 10-8cm; consequently, solids are almost incompressible. In addition, the intermolecular attraction in solids is quite high and for that reason the movement of atoms or molecules in solids is restricted. As a result, atoms or molecules in solids have no freedom of mobility; they only vibrate in their fixed positions.
|
|
|
| Consequently, a solid will have a definite volume and shape. A solid can form a firm and rigid structure, which allows it to be cut into many shape and sizes. This can result in a solid having any number of free surfaces. A Solid will also have high density, incompressibility and a high melting and boiling point. A solid may be converted to a liquid when it is given heat energy.
|
|
|
| A solid
|
has a definite characteristic shape
|
|
tends to resist deformation of its shape
|
|
is relatively non-compressible
|
| Example: Diamond
|
|
|
| Solids can be classified as:
|
|
Crystalline
|
|
Amorphous
|
|
|
| In a crystalline substance, a definite well-defined external geometric shape such as cube, octahedron or tetrahedron characterizes the solid.
|
|
|
|
|
|
| Internally, particles are orderly arranged in a three-dimensional pattern.
|
| Example: Common salt and copper sulphate
|
|
|
| Amorphous solids (solids without definite structure) do not exhibit clear-cut external geometrical shapes. Their internal particle arrangements are less regular; they do not have a defined melting point and display a tendency to deform more easily.
|
| Example: Glass and plastic.
|
|
|
| Glass does not resist deformation very well. It softens rather than melts when heated and sags and flows on heating over a long period of time.
|
|
|
| Liquid State
|
| In liquids, the intermolecular space or the void is slightly more than that of solids while the intermolecular attraction is less. The average distance between particles is of the order 10-7 to 10-5 cm. When compared to solids, the particles of liquids are relatively loosely packed. This type of packing leads to a greater mobility of the molecules and liquid particles can move about but cannot separate and so can flow.
|
|
|
| As a result, a liquid has a definite volume but no definite shape. It takes the shape of the container in which it is placed. As the intermolecular space is not much, like solids, a liquid cannot be compressed much, even if high pressures are applied. A liquid has only a single free surface the layer that is exposed to the surroundings. The boiling point of a liquid is above room temperature. The liquid state is an intermediate state between solids and gases.
|
|
|
|
|
|
| A liquid
|
|
has a definite volume
|
|
no characteristic shape
|
|
takes the shape of the container
|
|
is fluid - is able to flow and change shape without separation
|
|
is essentially non-compressible
|
| Example: Water and milk
|
|
|
| Gaseous State
|
| In gases, the intermolecular attractions are very poor. The particles are loosely packed at random and the voids between particles are very large. As a result, a gas does not have a definite shape or a definite volume. It will assume the shape and the volume of the container in which it is placed. Even if a very small quantity of a gas is introduced into a large vessel, the gas fills the whole of the vessel. As it fills the whole container it takes the shape of the container and has no surface of its own. We say that the gas has no free surface. Unlike solids and liquids, a gas is highly compressible. For a definite mass of a gas, its volume depends on the pressure and the temperature.
|
|
|
| Effect of Temperature and Pressure on States of Matter
|
| A gas
|
|
has no definite volume or shape
|
|
is a fluid
|
|
is highly compressible. It takes the volume and shape of the vessel in which it is kept.
|
| Example: Oxygen, Hydrogen and Carbon dioxide
|
| |
| |
|
|
|
|
| Characteristics of the Three States of Matter
|
|
|
|
|
|
|
| A fourth state called plasma refers to the super heated gaseous state. This state is a mixture of electrons and positively charged ions with unusual properties. It is found at extremely high temperatures such as interiors of the sun or stars. Astronomers reveal that 99% of all matter in the universe is present in the plasma state.
|
|
|
| Super Cooled Solid State
|
| A fifth state has recently been revealed that refers to the super cooled solid. In the super cooled state atoms lose their separate identity and get condensed. They behave like a single 'super atom'. The existence of this state was first envisaged in 1925 by Albert Einstein, who based the idea on the work by Satyendra Nath Bose, the Indian physicist, who had predicted a class of fundamental particles called 'BOSONS' that were named after him. A 'Super atom' was actually created on the 5th of June 1995 by the scientists Wieman and Cornell. They chilled atoms of a gas, to the lowest temperature ever achieved, and created a new state of matter called BOSE-EINSTEIN CONDENSATE. Using lasers and an exotic evaporation method, they plunged the temperature of RUBIDIUM gas almost to 'absolute zero' or -273oC. All atomic motions come to a stand still at this temperature.
|
|
|
| We shall concern ourselves with the study of matter in the three main states i.e., solid, liquid or gas. The fourth and fifth states of matter are beyond the scope of our study.
|
| |
