States of matter solids, liquids and gases

To understand the various states of matter and their connection to each other, we must understand the meaning of the word mo­lecule.

We can divide a piece of material into small parts and then sub­divide each of these small parts into still smaller parts. We shall continue this process of division until the parts become very, very small. In the end they will become so small that it will be impos­sible to divide them further. We call these smallest particles atoms. They are the fundamental building blocks of all materials and they have a definite attraction for each other.

Atoms combine into molecules and molecules may contain one, two, three and more atoms. In metals there is only one atom in a molecule, for example.

The molecules of a solid are very close together and have a great attraction for each other. The -closer they are together, the heavier is the solid; however, the molecules are in a state of continual vibra­tion. In this state their attraction for each other is very great, and that is why it is very difficult to change the shape of a solid.

Now, if we heat the solid, the molecules begin to vibrate more and more and therefore there is less attraction for each other. Thus, a solid expands when we heat it. When the molecules are quite far apart from each other, the solid changes into a liquid.

If we continue to heat the liquid, the molecules begin to vibrate so strongly and they move so far apart from each other that they will have very little attraction for each other. Now the liquid be­comes a gas which has no definite size.

The three states of matter — solid, liquid and gaseous — are very close to each other and more heat or less heat will change the substance from one state to the other. Ice, water and steam are examples of this change of state.

ПОЯСНЕНИЯ К ТЕКСТУ

...have a great attraction for each other сильно притягивают друг друга

They move so far apart from each other они так далеко отодвигаются друг от друга

What is an electron?

What is an electron? We can think of the electron as a very small, indivisible, fundamental particle—a major constituent of all 'matter. All electrons appear to be iden­tical and to have properties that do not change with time. Two essential characteristics of the electron are its mass and its charge. Qualitatively, we can think of an electron as a "piece of matter" that has weight and is affected by gravity. Just as the mass of any object is defined, we can define the mass of the electron by applying a force and measuring the resulting rate of change in the velocity of the electron, that is, the rapidity with which its velocity changes. This rate of change is called acceleration, and the electron mass is then defined as the ratio of the applied force to the resulting acceleration. The mass of the electron is found to be about 9.11 X 10-²⁸grams.¹Not only the elec­tron but all matter appears to have positive mass, which is equivalent to saying that a force applied to any object re­sults in an acceleration²in the same direction as the force.

How does the other aspect, the charge of the electron, arise? If we investigate further, we find that all electrons have an electric charge, and the amount of charge, like the mass, is identical for all electrons. No one has ever succeed­ed in isolating an amount of charge smaller than that of the electron. The sign of the charge of the electron fs con­ventionally defined as negative; the electron thus represents the fundamental unit of a negative charge.

No experiment has yet succeeded in removing the charge from the electron, leaving only its mass. Therefore, instead of considering the electron a "massive" body that has some-how acquired a charge, it seems more realistic to think that the charge and the mass are two inseparable aspects of a single unity.

The motion of an electron, like that of any other body, results from a force acting on it. How can force be applied to an electron? One way is by gravity. Another is by bring­ing a second charge near the electron, thus exerting an at­tractive or a repulsive force on it. In this case we may say that the second charge sets up an electric field which ap­plies a force to the first charge. Finally, we find that an electric current flow will affect the motion of a nearby charge, but only if that charge is already in motion. In this case, we say that the current sets up a magnetic field which applies a force to the moving charge. These three are the only known ways of applying force to an electron. The relationship between these fields, the charges pro­ducing them and the resulting effects on other charges are the Jaws orelectron motion.

Notes

1. 9.1 IX 10-²⁸grams—nine point eleven multiplied by ten to the minus twenty-eighth power

2. to result in an acceleration — вызыватьускорение