Models of the atom. The dot at the center of the Rutherford atom is the nucleus. The size of the dot is enlarged so that it can be seen in the figure.

      What results would be expected for such an experiment? It depends on how the atom is organized. A prevailing model of the atom at the time (the Thomson, or “plum-pudding,” atom) proposed that the negatively charged electrons (the plums) were mixed with smeared-out positive charges (the pudding). This model explained the neutrality of bulk material, yet still allowed the description of the flow of electric charges. In this model, it would be very unlikely for an alpha particle to scatter through an angle greater than a small fraction of a degree, and the vast majority should undergo almost no scattering at all.

      The results from Rutherford’s experiment were astounding. The vast majority of alpha particles behaved as expected, and hardly scattered at all. But there were alpha particles that scattered through angles greater than 90 degrees, incredible in light of expectations for a “plum-pudding” atom. It was largely the evidence from this type of experiment that led to the model of the atom as having a nucleus. The only model of the atom consistent with this Rutherford experiment is that a small central core (the nucleus) houses the positive charge and most of the mass of the atom, while the majority of the atom’s volume contains discrete electrons orbiting about the central nucleus.

      Under classical electromagnetic theory, a charge that is moving in a circular path, loses energy. In Rutherford’s model, the electrons orbit the nucleus similar to the orbit of planets about the sun. However, under this model, there is nothing to prevent the electrons from losing energy and falling into the nucleus under the influence of its Coulomb attraction. This stability problem was solved by Niels Bohr in 1913 with a new model in which there are particular orbits in which the electrons do not lose energy and therefore do not spiral into the nucleus. This model was the beginning of quantum mechanics, which successfully explains many properties of atoms. Bohr’s model of the atom is still a convenient description of the energy levels of the hydrogen atom.

      Ex. 1 Make the following sentenses negative.

      1. Becquerel decided to develop his photographic plates. 2. In this model, it would be very unlikely for an alpha particle to scatter through an angle greater than a small fraction of a degree. 3. The size of the dot is enlarged so that it can be seen in the figure. 4. The results from Rutherford’s experiment were astounding. 5. By the early 20th century, there was rather compelling evidence that matter could be described by an atomic theory.

      Ex. 2 Make up questions to which the following sentences are the answers.

      1. At high enough energy, the addition of energy creates new particles rather than frees the quarks. 2. Bohr’s model of the atom is still a convenient description of the energy levels of the hydrogen atom. 3. Energy brought into a nucleus to try to separate quarks increases the force between them. 4. This hypothesis was disproved on the 26-27th of February, when his experiment “failed” because it was overcast in Paris. 5. Because gamma rays carry no electric charge, they can penetrate large distances through materials. 6. A sheet of aluminum one millimeter thick or several meters of air will stop these electrons and positrons.

      Ex. 3 Give Russian equivalents of whether. ..

      1. The question is whether he will send you to the conference or go himself.

      2. Whether the project will be approved at present is a matter of importance.

      3. One of the fundamental questions is whether petroleum migrated over considerable distances to form pools, or whether it was formed essentially in place. 4. There was a disagreement whether they should continue along the same line or whether they should take another approach. 5. Whether this difference of approach played a decisive role in the final solution to the problem remains a subject for speculation. 6. One of the fundamental problems of today is whether we will be able to meet the challenge of the environmental crisis.

      Ex. 4. Fill in the blanks with the proper words from the list below

      1. World science is faced with the all-important task of finding effective … of protecting the atmosphere from pollutants. 2. The data available to man concerning the physical phenomena of space might not be very exciting to those who cannot interpret their … 3. Natural scientists are so interested in their selfmade problems that they tend to neglect the problems that are most.. for human life. 4. The name atom comes from the Greek word and.. indivisible. 5. The information on the physical phenomena of space is a part of the answer to space exploration, but is.. the total explanation 6. Radar techniques have recently been employed to obtain more accurate measurements of the.. distance between the Earth and the Sun. 7. The main task of ecology is to support survival of plant, animal and human life …

      means, meaning, meaningful, means, by no means, by all means, mean.

      Ex. 5 Translate the sentences into English using who, which, which of, what

      1. Трудно найти человека, который бы не задумывался над этим. 2. Это вопрос, который касается всех. 3. Трудно сказать, какая из этих проблем сложнее. 4. Необходимо решить, кто из них возглавит эту работу. 5. Трудно сказать, какие вопросы будут нас волновать через два десятка лет. 6. Никто не знает, кто первым применил это устройство. 7. Лектор сказал, какую литературу надо прочитать по этому предмету. 8. Трудно было решить, кто из них был прав.

      Ex.