4. The First and the Most Surprising
Hydrogen was discovered by the famous English physicist the Hon.
Henry Cavendish. He was the richest of the learned and the most learned
of the rich, as one of his contemporaries put it. We might add that he was
the most punctilious of scientists. It is said that whenever Cavendish
borrowed a book from his own library he always signed his name on the
book card. The most sedate of scientists, devoted entirely to scientific
research, always engrossed in his science, he got the reputation of an eccentric recluse.
But it was just these qualities that enabled him to discover the new gas hydrogen. And,
believe us, it was no easy task!
He made his discovery in 1766, and by 1783 the French Professor Charles had flown
the first hydrogen-filled balloon.
Hydrogen was a most valuable find to chemists, too. It helped them to get an insight
into the structure of acids and bases, these most important classes of chemical
compounds. It became an indispensable laboratory reagent for precipitating metals from
solutions of salts, and for reducing metallic oxides. And paradoxical though it seems, had
hydrogen not been discovered in 1766, but, say, half a century later (such a thing could
really have happened) the progress of chemistry, both in theory and practice, would have
been retarded for a long time.
When the chemists had come to know hydrogen well enough, and practical workers had
begun to utilize it for the production of important substances, this gas drew the attention
of physicists. And they found out a great deal of information which enriched science
many times over.
Do you need more evidence? For one thing, hydrogen solidifies at a lower temperature
than any other liquid or gas (except helium), at minus 259.1° Celsius. Secondly, the
hydrogen atom enabled the Danish physicist Niels Bohr to work out a theory of the
arrangement of electrons around the atomic nucleus, without which the physical sense of
the Periodic Law could not have been understood. And these facts laid the foundation for
other very important discoveries.
And hydrogen takes up its abode in the seventh group. But not for long. After getting to
know its new relation a little better one of the halogens remarks a little disappointedly:
"See here, brother. You don't seem to have many electrons in your outer shell, do you?
Only one as a matter of fact - like them blokes in group one. Hadn't you better get back to
the alkali metals?"
See what difficult straits hydrogen is in: there are plenty of rooms but none it can
occupy permanently, with full rights. But why? What is the reason for this surprising
two-facedness of hydrogen? What makes hydrogen behave so eccentrically?
The specific properties of any chemical element become evident when it combines with
other elements. It then yields or accepts electrons which either leave its outer shell or
enter it. When an element loses all the electrons of its outer shell, the rest of its shells
usually remain unchanged. Such is the case with all the elements except hydrogen. When
hydrogen parts with its only electron, all that remains is its atomic nucleus. What is left is
a proton, this being, as a matter of fact, all the hydrogen atom nucleus consists of.
(Actually it does not always consists of only a proton, but we shall come to this important
point later.) Hence the chemistry of hydrogen is the only chemistry of its kind, as it were,
the chemistry of an elementary particle, the proton. Thus, reactions involving hydrogen
proceed under the influence of protons. And that is why hydrogen behaves so
inconsistently.
Another remarkable property of hydrogen is that its atom emits radiations having a
wavelength of 21 centimetres. This is called a universal constant because it is the same
throughout the universe.
And scientists have taken up the problem of organizing radio communications with
other inhabited worlds on the hydrogen wave. If these worlds are inhabited by intelligent
creatures, they should have an idea of what 21 centimetres is.