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64. What Humphry Davy Did Not Know

The list of scientific works of the famous English chemist Humphry Davy is very long indeed.

He was not only a talented scientist, but an ingenious investigator as well. Whatever problem Davy undertook he almost always solved it successfully. He prepared not a few new chemical compounds and developed several new methods of investigation. Finally, Davy discovered four elements, namely: potassium and sodium, magnesium and barium.

One of his works is a short paper reporting the preparation of a simple chemical compound, chlorine hydrate, in which six molecules of water are combined with the chlorine molecule: Cl2 • 6H2O.

Though Davy studied the properties of this substance very thoroughly, he never knew that he had obtained a compound of an entirely new type, a compound without chemical bonds.

This became clear only to chemists of the twentieth century. They attempted to account for the existence of chlorine hydrate according to the modern conception of valence. But they failed: the substance was too hard a nut to crack, nor was it the only one.

For decades chemists sought the answer to the question whether the inert gases were really so hopelessly inert, or whether they could somehow be made to enter into chemical reactions. We already know the answer to this question. But while it was still a question scientists succeeded in preparing several hydrates of argon, krypton, xenon, and radon.

These hydrates contained no ordinary chemical bonds. Yet many of them are comparatively stable substances.

The simple organic compound urea was another riddle to chemists. It combined readily with many hydrocarbons and alcohols. This strange “friendship” evoked surprise: what forces could cause urea and alcohol to attract each other? Anything but chemical forces....

Be that as it may, but the new class of compounds, substances not containing chemical bonds, grew at a terrific rate.

However, there turned out to be nothing supernatural about it.

The two combining molecules are not equal. One of them acts as the “host”, and the other as the “guest.”

Host-molecules form a crystal lattice. There are always interstices in this lattice not filled with atoms. The “visiting” molecules enter these interstices. But the hospitality is of a rather strange kind. The strangers stay with their host for a very long time, because it is not easy for them to leave the interstices of the crystal lattice.

In this way, molecules of the gases chlorine, argon, krypton and others get trapped, as it were, in the interstices of the crystal lattice of water

Now chemists call these and a number of other substances not having chemical bonds between different molecules clathrate (or cellular) compounds.

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by Ian Ellis
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