VII. Reading and comprehension.

Exercise 18. Read the text C without a dictionary for 4 min.

Text c “States of matter and its molecular and atomic constitution”

According to the law of conservation of matter, matter can neither be created nor destroyed. Matter can exist in three physical states, namely solid, liquid or gaseous. As a solid it has definite form and volume not easily changed by mechanical force. As a liquid it has no definite volume, but being fluid it takes the shape of its container. A gas has neither definite volume nor shape.

All matter — whether solid, liquid or gas — is made up of very small particles called molecules. Molecules in turn are made up of atoms, which are still smaller particles. The history of the atom goes back to the time of, the Greek thinker Democritus. He thought that all substances were made up of tiny particles or atoms which could not be further divided. It was at the beginning of the nineteenth century that the scientists first established experimentally the atomic theory of the structure of matter. They found that the simple forms of matter were chemical elements which consisted of atoms — inivisible particles of very small size. Then scientists discovered that the atom was further divisible and it was not the smallest thing in the world.

Because atoms are so very small their number must be extremely large. An atom holds a tremendous force hidden in its tiny body.

The atom helps us to fly through the vast outer space. Atomic energy is enabling scientists to study cosmic rays and other phenomena in outer space.

Commentary

neither ...nor ... – ні … ні in turn – в свою чергу

Exercise 19. Fill in the tables.

States of matter

Shape and volume

Structure of matter

Exercise 20. Speak on the states of matter and its structure.

Exercise 21. Characterize the atom using the table.

Structure

properties

application

Exercise 22. Discussion points.

1. The development of science of chemistry.

2. Chemistry of today.

3. Constitution of matter.

SUPPLEMENTARY READING

Text D.

THE DISCOVERY OF THE NUCLEI ATOMS

In 1911 E. Rutherford carried out the experiment that showed that most of the mass of atoms is concentrated in particles that are very small in size compared with the atoms themselves. His experiment consisted in bombarding a film of some substance, a piece of metal foil, with a stream of fast-moving alpha-particles, and observing the direction in which the alpha-particles rebound from the atoms.

If the atoms bombarded with alpha-particles were solid throughout their volume, we should expect all of the alpha-particles in the beam to be deflected to some extent. Actu­ally, however, E. Rutherford observed that most of the alpha-particles passed through the metal foil without ap­preciable deflection.

Later Rutherford found that the heavy nucleus has a cross-sectional area only 0.00000001 as great as the cross-sectional area of the atom, and hence that the diameter of the nucleus is only 1/10,000 as great as the diameter of the atom. The picture of the atom that has been developed from experiments is an extraordinary one. If we could magnify a piece of gold leaf by the linear factor 1,000,000,000—a bil­lion fold—we should see it as an immense pile of atoms about two feet in diameter, each atom being about as big as a bushel basket. Practically the entire mass of each atom would, however, be concentrated in a single particle, the nucleus, about 0.001 inch in diameter, like an extremely small grain of sand. This nucleus would be surrounded by electrons, equally small, and moving rapidly about.