chemical elements and their compounds - Sciencemadness Dot Org

GROUP I
HYDROGEN, DEUTERIUM, AND TRITIUM
HYDROGEN, the lightest of the elements, was one of the chief
problems of the original Periodic Table, since it has close affinities
both with the alkali metals of Group I and with the halogens of
Oioup VII. We now realize that it stands at the head of both groups,
resembling the alkali metals in having a single easily detached electron,
and the halogens in having one electron less than the next following
inert gas. It thus occupies a unique position in the Table.
The amount of hydrogen in the earth's crust, including the water and
the air, is estimated at 0*87 per cent, by weight and 15*4 per cent, by
atoms. Free hydrogen occurs to a minute extent in the atmosphere
{according to Paneth 1 less than 1 part in a million by volume); it is continually
being produced on the earth's surface from various sources, including
oil gas outflows, but at the same time the molecules move quick
enough to escape from the earth's gravitational field (see above, p. 2).
Natural gas may contain up to 10 or even 30 per cent, of hydrogen, the
remainder being mainly methane and ethane. Commercially hydrogen can
be obtained from this source or from coal gas (of which it forms some
50 per cent.) by liquefying the other components, but it is more often got
(for example in making synthetic ammonia) from water gas, which is a
mixture of hydrogen and carbon monoxide, made by passing steam over
heated coal or coke; if this is mixed with more steam and passed over
it suitable catalyst (oxides of iron and cobalt are commonly used) at a
temperature not above 400° C, the carbon monoxide reacts with the steam
to give carbon dioxide and hydrogen. The carbon dioxide is removed by
washing with water under pressure, and the residual carbon monoxide by
treatment with ammoniacal cuprous solution, or by passing over heated
noda lime, which reacts with it to give sodium formate.
Hydrogen occurs in a surprisingly large number of forms.
I. There are three known isotopes of hydrogen, of mass-numbers 1, 2,
And 3. The first two of these occur in nature in the proportions roughly
Of 0,000 to 1; the third is now known not to occur in natural hydrogen
In detectable amounts, but it can be made by atomic bombardments, for
iiutmple, of deuterium by deuterons. These isotopes are distinguished as
tProtium, Deuterium, and Tritium; but the properties of pure protium and
lt« compounds are practically identical with those of the natural isotopic
mixture. The peculiar properties of deuterium, and so far as they are
known of tritium, are described in the next sections (deuterium, p. 36;
tritium, p. 57).
1 F, A, Paneih, Nature, 1937, 139, 181.