Words to be remembered:

interior volatile

average to escape

motion constant

sufficient within

surface velocity

vapour thereafter

evaporation wander

№12

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 progress. 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.

Words to be remembered:

interior therefore

opaque transparent

ductile branch

break conduct

insulator previously

№13

Solid state (II)

If we consider the fact known since the earliest studies of electric currents, we should remember that metals conduct electricity well and most materials do not.

It is only the discovery of electron that could help the scientists to understand some of these facts well. With the dis­covery of electron it was assumed that in metals some or all of the atoms had lost an electron and that in insulators such as glass they had not. The electrons in a metal proved thus to move freely, whereas the electrons in insulators do not. Why did this happen in metals? This very question had to await the discovery of quantum mechanics. The next question was: “How are the electrons arranged?”

As far as this question is concerned we can say that solids can be divided into two classes: crystalline and amorphous. In the crystalline group, which is the largest and includes the metals and most minerals, the atoms are arranged in a regular way. In some metals (for instance copper and nickel) they are backed together. In other metals (such as iron, for example), they are arranged in the form of a cube. The commonest of the amorphous group of solids appear in glass, its atoms are put together in a more disordered way than those of a metal.

The structure of an amorphous material is much more difficult to discover than that of a crystalline solid and considerable effort is being made to learn more about the arrangement of atoms in such materials.

Much has been learned about solids but much is still to be learned. There is a number of problems which are to be solved. No wonder that many scientists have been working at this inte­resting, so-called “solid state” science.