States of Matter

Topics: Atom, Force, Energy Pages: 10 (1866 words) Published: August 21, 2013
General Introduction to Matter

Matter is defined as any mass that occupies space. Matter is made up of particles called atoms. Matter has inertia because it has mass, and because of that it has weight. The existence of atoms – proven by the Brownian motion. (read more….) Matters can exists in the following states: (i) Solid (ii) Liquid (iii) Gas A material can change from one state to another e.g. liquid to gas, solid to liquid.

A solid is an object that is rigid and by itself can retain a fixed shape and volume     

Atoms are arranged in an orderly fashion and very close to each other. Forces between atoms are strong (repulsive and attractive). Atoms are ‘locked’ in a certain position and are not able to move freely so solids are able to retain their shape. Atoms just vibrate in their respective equilibrium positions. At constant temperature, solids have definite shape and are not able to deform easily.

A liquid is a fluid which has a fixed volume but no definite shape  

Molecules in a liquid are not arranged in an orderly fashion. That’s why liquid has no fixed shape and it takes the shape of its container that holds it and is able to flow. The volume of a liquid is constant at constant temperature. The molecules in a liquid have a higher internal energy than molecules in a solid and the molecules in a liquid are able to drift slightly away from its equilibrium position in a random manner. It’s atoms are no longer perpetually ‘locked’ firmly in a particular position and that is why liquid can retain its shape.


A gas does not have a fixed volume and has no definite shape 

Molecules in a gas move freely and randomly. A gas has no definite shape and it takes the shape of its container. Its volume is equal to the volume of the container Gas is formed when a liquid is heated until the temperature reaches the boiling point. Further heating will cause the liquid to vaporize resulting in a phase change of the material/substance.

Molecular Bonding

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A solid has definite shape, whereas liquids and gas takes the shape of the container that holds it. This shows that molecules are bound to each other. By a molecule it means that a group of two or more atoms that are strongly held together so as to function as a single unit. When atoms make such an attachment, we say that a chemical bond has been formed. In general, there are basically four kinds of molecular/chemical bonding: (I) Ionic bond (II) Covalent bond (III) Van der Waals bond (IV) Hydrogen bond

Intermolecular Forces

The forces that bind the atoms or molecules are electrostatic in nature so there are repulsive and attractive forces that acts between two molecules/atoms.

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Originally, the two atoms are separated by a distance of r0. At one instant , one atom might have moved slightly further away from the neighbouring atom through a distance r1. [r1 > r0 ] When this happens, an attractive force acts on it. This force increases with distance so the further the atom is from its neighbour, the greater will be the attraction. It will be pulled back by the strong attractive force, thus preventing it from escaping.

Intermolecular Forces

Intermolecular Forces
Figure below shows the variation of attractive force Fattractive with the separation r between two atoms.

Intermolecular Forces
At one instant, one atom might moved slightly closer to the neighbouring atom through distance r2 where r2 < r0  When this happens, a repulsive force will act on it. This force increases when the separation decreases. The closer the atom is to its neighbour, the greater will be the repulsion.  Hence, it will be pushed back by the strong repulsive force to prevent it from crashing into its neighbouring atoms. 

Intermolecular Forces

Intermolecular Forces
Figure below shows the variation of repulsive force Frepulsive with the...
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