- •Chemistry
- •Introduction
- •Some facts about chemistry
- •Some facts about atoms (I)
- •Some facts about atoms (II)
- •The atomic model
- •The nature of ceramics
- •Construction materials
- •The measurements in chemistry
- •The metric system
- •Isotopes
- •Words to be remembered:
- •Notes on the text:
- •Liquids(I)
- •Words to be remembered:
- •Liquids (II)
- •Words to be remembered:
- •Solid state (I)
- •Words to be remembered:
- •Solid state (II)
- •Words to be remembered:
- •Properties of solids
- •Notes on the texts:
- •Words to be remembered:
- •Organic chemistry
- •Word to be remembered:
- •Elementary carbon
- •Words to be remembered:
- •Notes on the texts:
- •Carbon dioxide
- •Words to be remembered:
- •Words to be remembered:
- •Hydrogen
- •Words to be remembered):
Liquids (II)
The molecules within the interior of a liquid have a definite average energy of motion, and thus a definite average velocity at each temperature. Some of them, however, at any given instant, have a velocity sufficiently greater than the average velocity to enable them to break through the surface layer of molecules and escape. Thereafter they are free to wander about in the space above and constitute a vapour - namely a gas that
can be condensed to a liquid merely by increasing the pressure upon it. (Air is not a vapour, for to condense it to a liquid it must be both compressed and cooled).
The escape of the molecules from a liquid into its vapour is called evaporation. After a sufficient number of molecules have collected in the space above the liquid, their haphazard wanderings bring them back to the surface as fast as other molecules escape. Thereafter, there is a balance between evaporation and recondensation and thus a constant number of molecules within the closed space at any given moments; and these, by bombardment of the walls of the vessel set up a constant pressure, called the vapour pressure.
Words to be remembered:
interior volatile
average to escape
motion constant
sufficient within
surface velocity
vapour thereafter
evaporation wander
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Solid state (I)
If you take a paper clip and bend it would stay bent, it wouldn't, spring back and it wouldn’t break. The metal of which the clip is made is ductile. Some other materials are not ductile at all. If you tried to bend a glass rod (unless you are holding it in a flame), it would simply break. It is brittle. In this respect as in many others, glass behaves quite differently from a metal. The difference must lie either in the particular atoms of which metals and glass are made up or in the way the are put together, probably both. There are of course many other differences between metals and glass.
Metals, for example, conduct electricity and therefore are used for electrical transmission lines, glass hardly conducts electricity at all and can serve as an insulator. Glass being transparent, it can be used in windows whereas a sheet of metal even more than a millionth of an inch thick is quite opaque.
It is of course interesting to understand the reasons of these differences in behaviour.
During the past 20 years studies of this kind have been called solid-state physics, or sometimes since the subject includes a great deal of chemistry, just “solid state”. It is a major branch of science that has revealed new and previously unsuspected properties in metals. Solid-state physics has become one of the most important branches of technology. It has given rise to technological progresse. Having studied this branch of technology, engineers could understand much better the phenomenon of quantum mechanics as it is applied to solids. Though solids, of course, were the subject of experimental investigation long before quantum mechanics was invented.