Stories About Chemistry
24. Has Nature Been Just?
Today scientists say that all the chemical elements known to nature can be detected in any mineral sample. All without exception. Of course their proportion varies immensely.
But why is there so much of some and so little of others?
In the Periodic System all the elements have equal rights. Each occupies its own definite place. But when it comes to the terrestrial reserves of the element, these equal rights vanish into thin air.
The light elements of the Mendeleyev Table, its first thirty or so representatives, at any rate, constitute the bulk of the Earth’s crust. But there is no equality among them either. Some are more abundant, others less. For instance, boron, beryllium and scandium are among the very rare elements.
Since the Earth has been in existence there has been something of a “revision” of the supplies of its elements. A considerable amount of uranium and thorium has disappeared owing to their radioactivity. A large amount of the noble gases and hydrogen has been lost to outer space. But the general picture has not changed.
The scientists of our days write that the abundance of the chemical elements in the Earth’s crust decreases regularly from the light elements to the medium-weight ones and then to the heavy ones.
This isn’t always the case. For example, there is much more heavy lead on Earth than many of the light representatives of the Mendeleyev Table. Why so? Why not equal amounts of all? Has not nature been unjust in “accumulating” some of the elements and not attending to the supplies of others?
No, there are laws according to which there is bound to be a great deal of some of the elements and little of the others. To be quite honest about it, we do not know these laws as yet, and content ourselves with assumptions.
You see, the chemical elements have not always existed. The universe is so constituted that there is always a gigantic process of formation or synthesis of elements going on in various parts of it, a process so great that there is nothing it can be compared to. The cosmic nuclear reactors, the cosmic accelerators, are the stars. Chemical elements are always being “cooked” in the depths of some of them.
Unheard of temperatures, unimaginable pressures reign there. The basic laws are those of nuclear chemistry, the rules - nuclear chemical reactions transforming one element into another , the light elements into heavy ones.
And such are these laws that some elements form more easily and in greater quantities while others form with greater difficulty and therefore in smaller proportions.
It all depends on the stability of the different atomic nuclei. In respect to this nuclear chemistry has a quite definite opinion. The nuclei of lightelement isotopes contain almost equal numbers of protons and neutrons. Here these elementary particles form very stable structures. That is why the light nuclei are easier to synthesize.
In general, nature tends to create systems of the highest possible stability. They are easier to synthesize but participate less readily in nuclear reactions resulting in nuclei with larger charges. Nuclei of the latter kind contain considerably more neutrons than protons, and therefore nuclei of medium and heavy mass have no very great stability to boast of. They are more subject to the rule of chance, more inclined to change, and are therefore incapable of accumulating in very large quantities.
According to the laws of nuclear chemistry the higher the charge on the nuclei, the more difficult such nuclei are to synthesize, and therefore the less of them is formed.
The chemical composition of our Earth is like a silent replica, a voiceless reflection of the dynamics of the laws governing the process of origination of the elements.
When scientists have learned these laws in full, we shall understand why the different chemical elements differ so widely in abundance.