Isotopes are different types of a chemical element in the composition of the nucleus

Human memory is built on associative-logical connections. Therefore, it is so important for us to streamline the reality, distribute its elements by cells and find a system. Otherwise, memory refuses to obey, and reason - to analyze. It is no coincidence in the history of chemistry such an important breakthrough is the creation of the periodic table - order, system and logic triumphed. The influence of this discovery was so great that it inspired many. For example, Lyubishchev, the genius of Russian time management, developed his system in order to create a periodic table of living organisms. This goal was not achieved, but the fact itself proves the importance of logic for human understanding. But reality is richer than beautiful schemes. For example, in the main table of chemistry, some elements stand in violation of the order of mass. Why? You can answer one word - "isotopes". This word literally means "occupying one place".

Many worked, do not remember all

Mendeleyev's table is the fruit of the painstaking work of many scientists, and not only of its creator. He brilliantly created the principle itself and found the basic patterns. But the figure of the mass, which you see under each element - the fruit of the work of many chemists, and in addition, it is inaccurate. How can this be? Perhaps you have ever noticed that the atomic number is a beautiful whole number. But the mass is fractional with a huge number of decimal places. Why? And the same isotopes are to blame. This is explained quite simply. If you look at the numbers for the "nitrogen" element, you will see the figure of the atomic mass at 14,0067. However, if you "catch" a free nitrogen atom, it can weigh 10 and 25 atomic units. They are different. And what is the difference? The mass of an isotope consists of a mass of protons and a mass of neutrons. The mass of protons is a constant value, it makes the element an element (nitrogen-nitrogen). But with neutrons, an atom can be both rich and poor. In the example with nitrogen, they can be 18, and only 3 pieces. Isotopes are types of element atoms depending on the number of neutrons in the nucleus. Nitrogen has 16 isotopes. Some other elements have more.

And what should a scientist do?

If you were scientists, how would you do? How would you record the mass in the table for calculations? It was, of course, possible to take the arithmetic mean. But many isotopes are very unstable objects, some of them are artificially created. Therefore, it would be wrong to make calculations with an orientation to inaccurate data. Scientists acted differently - they calculated the atomic mass of an element in proportion to the natural abundance of one or another isotope. As a result, the probability that, for an arbitrary search, you got an isotope of 14 mass units, it is very large. The nucleus of an isotope found by chance will most likely contain 7 protons and 7 neutrons.

Reasons for inaccuracy

Why is the atomic mass not quite accurate? Because the conclusion about it is made inductively - from the private to the general. We do not know the exact composition of the Earth under the crust, we did not explore geologically even the entire surface of the Earth geologically. Therefore the figure of the atomic mass is probabilistic. It is based on the knowledge that people have for today. Why does this satisfy the scientists? Because greater accuracy is needed only for molecular physics, for banal calculations of quantities, the error can be neglected. But the violation of the order of mass is announced by the fact that for the chemical properties of an important amount of charged particles - protons. And it is by the number of protons that the elements are arranged sequentially.