The first storey, or first period of the Mendeleyev Table, has only two rooms or boxes. The second and third have eight each. The next two stories (the fourth and fifth) have eighteen rooms each, like in a hotel. The two below that (the sixth and seventh) have even more rooms, thirty-two each. Have you ever seen such a building

   Still that is the form of the Big House of chemical elements known as the Periodic System. Architect's whim? Not at all! Any building has to be designed in accordance with the laws of physics; otherwise the least breath of wind will topple it over. The physical laws that underlie the architecture of the Periodic System are just as strict and decree that each period of the Mendeleyev Table shall contain a definite number of elements. For instance, the first period has two elements, no more and no less. That is what the physicists affirm and the chemists fully agree with them.

   But they didn't always agree. There was a time when the physicists said nothing, because the Periodic Law had not yet begun to bother them. But the chemists who were discovering new elements almost every year were finding it harder and harder to know where to put the newcomers. And there were annoying situations when there was a whole queue of claimants for the same box in the table.

   Not a few scientists were sceptical. They declared quite soberly that the edifice of Mendeleyev's Table was built on sand. One of these was the German chemist Bunsen, who developed the method of spectroscopic analysis together with his friend Kirchhoff. But when it came to the Periodic Law Bunsen exhibited surprising scientific shortsightedness. "One might just as well seek regularities in the figures of stock exchange bulletins!"  he snapped out once in a fit of anger.

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