Atomic mass: whimsical patterns

All the variety of existing substances is explained by combinations of different types of atoms. It so happened that the species of these atoms - a little more than a hundred for today. But they - the guys are pretty capricious, and unite with each other not according to the rules of combinatorics, but in accordance with the laws of chemistry. And still, the amount of substances is huge, it is growing. But the number of known chemical elements almost does not increase. Each of them is unique and has its own "portrait". And the main feature of every element is the atomic mass.

The unit of this mass is a very small number. None of the available types of atoms fit ideally as a candidate for being a unit of mass (but the lightest hydrogen was closest). As a result, scientists decided to take a number convenient for calculations - one-twelfth of the absolute mass of an element such as carbon. It turned out that this amount very well expresses the relationships in which the atoms of the elements are located to each other. So, the atomic unit of mass was recognized for the number in a very small degree, this is a small figure of "ten to the extent minus twenty-seventh."

It is clear that it is inconvenient to use such a number. You understand, in the calculations, this minus the twenty-seventh degree is not always carried from the hand, and as a result, the numbers can be just as uncomfortable, bulky. What to do? Apply a unit such as the relative atomic mass of the element. What is it? Everything is done very simply - the absolute atomic mass is taken (the number is extremely inconvenient, almost with the same minus degree), is divided into our one twelfth mass of carbon. So what? Correctly, the degrees are shortened and a quite decent number is obtained. For example, sixteen for an oxygen atom, fourteen for nitrogen. Carbon, logically, will have a mass of twelve. And the atomic mass of hydrogen is one, although not exactly one, which proves that it was not hydrogen that was taken for calculations, although the number, to its mass is very close.

Then why the relative atomic masses of each element - the numbers are not quite beautiful, not whole? The thing is that the elements, although they are species of atoms, within the species allow themselves some "diversity". Some of them are unstable, in simple terms, they are very easily spontaneously destroyed. But they exist for a while, so you can not ignore them. It happens, and the generally stable kind of elements includes subspecies with different atomic masses. They are called isotopes. This in translation means that they occupy one cell of the table known to every schoolboy - yes, you guessed correctly, Mendeleev's tables.

But does the atomic mass make the element an element? At all, the element is characterized by a much more fundamental number of protons in the nucleus. Here it can not be fractional and means a positive charge of the nucleus. The "quiet" atom of electrons has the same number as the protons in the nucleus, and therefore the self-respecting atom is electrically neutral. According to the charge of the nucleus, the atoms also line up in a sequence in the periodic table, but their masses sometimes do not obey this law. Therefore, there are cases of exceptions, when the heavier atom in the sequence of the table is earlier. Well, it's only the isotopes that are to blame for this. Nature "wanted" to have heavy isotopes for a given element. But the relative atomic mass is exposed proportionally to the amounts of different isotopes. Simply put, if there are more heavy isotopes in nature - the atomic mass will be larger, if more lungs - then less. So the paradoxes of the Mendeleyev system are obtained .

In fact, what has been said about the atomic mass is somewhat simplified. There are also deeper and more serious regularities concerning the periodic table. But they require a separate article, perhaps we will return to their consideration later, dear reader.