The middle of the last century marked the birth of a new era in the history of mankind. The Stone Age was once replaced by the Bronze Age, then the periods of the reign of iron, steam and electricity went on. We are now at the very beginning of the era of the atom. Even the most superficial knowledge in the field of the structure of the atomic nucleus opens unprecedented horizons for humanity.
What do we know about the atomic nucleus? The fact that it makes up 99.99% of the mass of the entire atom and consists of particles, which are commonly called nucleons. What are nucleons, how many of them, what are they, now every high school student with a solid four in physics knows.
How do we imagine the structure of the atom
Alas, a technique will soon appear that will make it possible to discern the particles that make up an atom, the atomic nucleus. There are thousands of questions to how matter is arranged, and there are also many theories of the structure of elementary particles. Today, the theory that answers most of the questions is a planetary model of the structure of the atom.
According to her, negatively charged electrons held by electric attraction revolve around a positively charged nucleus. And what are nucleons? The fact is that the nucleus is not monolithic, it consists of positively charged protons and neutrons - particles with a zero charge. Here they are, the particles from which the atomic nucleus is built, and it is customary to call nucleons.
Where did this theory come from if the particles are so small? Scientists came to the conclusion about the planetary structure of the atom, directing beams of various microparticles onto the thinnest metal plates.
What are its dimensions
Knowledge of the structure of an atom will not be complete if you do not imagine its elements on a scale. The nucleus is extremely small even compared to the atom itself. If you draw in your imagination an atom, for example, gold in the form of a huge balloon with a diameter of 200 meters, then its core will be just ... hazelnut. But what are nucleons and why do they play such an important role? Yes, if only because it is in them that the entire mass of the atom is concentrated.
In the nests of the crystal lattice, the gold atoms are located fairly densely, so the distance between neighboring "nuts" on the scale we have adopted will be about 250-300 meters.
Proton
Scientists have long suspected that the nucleus of an atom is not some kind of monolithic substance. The quantities of mass and charge, growing "steps" from one chemical element to another, were very striking. It was logical to assume that there are some particles with a fixed positive charge, from which the nuclei of all the atoms “accumulate”. How many positively charged nucleons are in the nucleus, so will its charge.
Assumptions about the complex structure of the atomic nucleus were made as early as Mendeleev’s construction of his periodic table of elements. However, technical capabilities in order to experimentally confirm the guesses did not exist at that time. Only at the beginning of the 20th century Ernest Rutherford set up an experiment confirming the existence of a proton.
As a result of exposure to matter by radiation of radioactive metals, a particle appeared from time to time - a copy of the nucleus of a hydrogen atom. She had the same weight (1.67 ∙ 10 -27 kg) and an atomic charge of +1.
Neutron
We came to the conclusion that it was necessary to search for another particle in absentia called a neutron. Since the question is how many nucleons are in the nucleus and what they are, lay in the uneven growth of mass and charge with a change in the serial number of the element. Rutherford made the assumption of the existence of a twin proton with zero charge, but he failed to confirm the guess.
In general, nuclear scientists already had a good idea of what nucleons and the quantitative composition of atomic nuclei are. And the elusive particle, while not yet discovered experimentally by anyone, was waiting in the wings. James Chadwick is considered to be its discoverer , who managed to isolate the "invisibility" from the substance, subjecting it to bombardment by helium nuclei dispersed to ultrahigh speeds (α-particles). The particle mass, as expected, turned out to be equal to the mass of the previously discovered proton. According to modern research, the neutron is a little heavier.
A little more about the "bricks" of the atomic nucleus
It is not difficult to calculate how many nucleons are in the nucleus of a chemical element or its isotope. Two things are necessary for this: the periodic table and the calculator, although it can be calculated in the mind. An example is two common isotopes of uranium: 235 and 238. These numbers indicate the atomic mass. The serial number of uranium is 92, it always indicates the charge of the nucleus.
As is known, nucleons in the nucleus of an atom can be either positively charged protons or neutrons of the same mass, but not having a charge. The serial number 92 denotes the number in the nucleus of protons. The number of neutrons is calculated by simple subtraction:
- - uranium 235, the number of neutrons = 235 - 92 = 143;
- - uranium 238, the number of neutrons = 238 - 92 = 146.
And how many nucleons can be put together at a time? It is believed that at a certain stage in the life of stars with sufficient mass, when the thermonuclear reaction is no longer able to restrain the force of gravity, the pressure in the interior of the star increases so much that it “sticks” electrons to protons. As a result, the charge becomes zero, and the proton-electron pair becomes a neutron. The resulting substance, consisting of "pressed" neutrons, is extremely dense.
A star weighing in our Sun turns into a ball with a diameter of a couple of tens of kilometers. A teaspoon of such a "neutron porridge" could weigh several hundred tons on Earth.