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.docTHE STRUCTURE OF THE ATOM
It is difficult to say definitely who was the first to say the word "atom"; perhaps, that was the ancient Greek philosopher Democritus (V-IV B.C.). The word "atom" comes from Greek and means "that which has no parts". The atom we know is far from being solid and indivisible, but we continue to use the word to designate the smallest particle which takes part in chemical interactions. 360
The origin of atomic physics as a branch of science can be attributed to Rontgen's discovery of X-rays. It was this discovery that enabled JJ. Thomson to complete his understanding of the generators of X-rays - the cathode rays or electrons. He found that not only did electrons striking matter generate X-rays, but that X-rays striking any kind of matter generated electrons. The discovery that electrons could be extracted from most dif-Iferent kinds of matter pointed to them as the substance of electricity. But this substance was made of individual particles - it was "atomic" - and it is this idea that led JJ. Thomson to take the first decisive step towards the discovery of the inner structure of the atom.
In 1903 JJ. Thomson advanced the first hypothesis concerning the structure of the atom. He suggested that atom is electrically neutral because it contains equal numbers of positive and negative charge carriers. These carriers are uniformly distributed throughout the atom as a whole and they occupy all the space in the atom, a sphere with the radius of 10'10 metre. The Thomson's model is often called the plum-pudding ['pudirj] model of the atom because the neutrons which neutralize the positive charge are supposed to be scattered around in the positive charge mass like raisins (изюминка) in a plum-pudding.
Thomson's model of the atoni structure was soon rejected, as it didn't account for the results of the experiments made by the Rutherford team. In 1910 two of Rutherford's workers, Geiger ['gaiga] and Marsden showed that the alpha particles, instead of going straight through thin sheets of matter were occasionally snot straight back. From this surprising result Rutherford drew a simple conclusion that the alpha particle must have hit something very small and very hard. He understood that atoms had nuclei. The nucleus was the other partner of the electron, and because the electrons were negatively charged, the nucleus must have a positive charge exactly equal to the total charge of the electrons around it. How were these electrons arranged? The problem had many strange analogies with that of the arrangement of the planets in the solar system and it pointed out to a similar solution. Rutherford's model of the atom was called nuclear atom or solar system atom. According to •Rutherford's theory the positive charge carriers in the atom are not uniformly distributed throughout the atom but are concentrated in a small region at its centre with
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