Friday, August 21, 2009



solid,liquid and gaseous states
water is one of the most common substances on our planet, the earth.All over the world, we find it in the solid, liquid and gaseous states or phases. In polar regions it is found as ice,the solid state.Rainwater is an example of the liquid state.Water vapour or gas exists in the air.Pools of water on the ground after rain gradually disappear; they evaporate slowly. Water vapour or steam is produced when a kettle boils
We can see a solid or a liquid. We can not see gas such as air. But the air makes leaves on trees moves some gases are coloured-chlorine gas, for example, is greenish-yellow.
All matter,that is anything which has mass or weight,is found in the solid, liquid or gaseous state. Some differences between the three states are as follows.
1.
Solids always have a constant volume and a constant shape. They can not be poured.
2. Liquids have constant volumes but they take the shape of the containing vessels. They can be poured.
3 Gases have no fixed shape but always occupy the whole volume of their container. They can be poured.
Molecules
If you scrape the surface of a piece of chalk, thousands of very tiny particles flake off and can be seen floating through the air. There is a limit to the size of particles the eye can see.
Dalton suggested the existence of molecules in matter. These are very tiny particles which together make up the whole of a solid or a liquid or a gas. The tip of a needle has many has many millions of molecules of the metal.
Molecules themselves are made up of atoms. Gifted scientists with imagination, such as sir J.J. Thompson and lord Rutherford, were able to make inspired guesses or theories about the particles inside atoms from experiment, although these particles can never be seen.
size of molecules
A rough estimate of the small size of a molecule was first made by Benjamin franklin about two hundred years ago. During a sea journey, he became interested in the way oil calmed the waves. Abouit 1770 he poured a teaspoon of oil on to the middle of the lake at clapham common, london. He saw the oil spread over a large area of water and estimated that it covered about 200 m2 . The oil film is estremely tin it can not be less than one molecule thick because molecules are the smallest part of a substance that can exist on their own in any circumstances.
Suppose the volume of oil was about 5 cm3.The area of 2000 m2 is 20 million cm2 or2*107.Hence the thickness of the oil film
= volume =5 cm3
area 2*107 cm2=2.5*10-7
So the size of a moleculewould not be bigger than 2.5*10-7 cm.
About a hundred years after Franklin's experiment, lord Rayleigh suggested that the certain oils spread over water in a film is one molecule thick.

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