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Introduction |
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Today the fact that all matter is made up of atoms is universally accepted. Realisation of the atomic constituents of matter began in 1828 when Scottish botanist Robert Brown observed a random ceaseless motion of pollen grains suspended in a liquid. Many macroscopic properties and phenomena observed can be explained using this microscopic picture of matter being composed of atoms or molecules possessing some form of motion. |
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Matter and Materials |
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Matter exists in several phases. If we look at all objects around us, we perceive that some materials have a definite shape and occupy a definite amount of space or volume. We call these materials solids and we can name many objects that are solids. We say that solids have a definite shape and a definite volume. |
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Evidence for Particulate Nature of Matter From Brownian Motion |
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Brownian motion can be demonstrated simply by releasing some smoke particles from burning cord into a small glass container and putting a cover plate to seal the smoke and air into the cell. |
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Diffusion |
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If a bottle of perfume is opened in one corner of a room, it spreads in the whole room by diffusion. If you drop a little ink in a beaker of water it will spread by itself in the beaker of water and the color spreads uniformly. |
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The States of Matter |
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The molecules in a solid are very closely packed. The inter-molecular force of attraction is very strong in solids. Hence solids have a definite size and shape. Molecules of a solid vibrate about their mean position. |
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Kinetic Theory of Gases |
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Molecules are in a state of perfect chaos, moving with all possible velocities in all directions, colliding with each other and with the walls of the container. |
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Properties of Matter |
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According to modern theory, the molecules of a solid are fixed in relation to each other. They vibrate in place, but do not wander around. This accounts for the fact that a solid keeps its own shape. Solids are usually crystalline. A solid is a crystalline substance in which the molecules, atoms and ions are believed to be arranged in definite geometrical patters. This geometrical pattern determines the shape of the crystal. |
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Summary |
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Materials can be solid, liquid or gaseous, depending upon the arrangement and freedom of movement of these particles. |
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