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 followed in succession. 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 up 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 that are commonly called nucleons. What are nucleons, how many of them, what they are, now every high school student who has a solid four in physics knows.
How do we imagine the structure of the atom
Alas, it will not be soon that a technique will appear that allows you to see the particles that make up an atom, an atomic nucleus. There are thousands of questions about how matter is arranged, and there are also a lot of theories of the structure of elementary particles. To date, the theory thatanswers most of the questions, is the planetary model of the structure of the atom.
According to it, negatively charged electrons revolve around a positively charged nucleus, held by electrical attraction. What are nucleons? The fact is that the nucleus is not monolithic, it consists of positively charged protons and neutrons - particles with zero charge. These are the particles from which the atomic nucleus is built, and it is customary to call them 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 by directing beams of various microparticles onto the thinnest metal plates.
What are its dimensions
Knowledge about the structure of the 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 imagine an atom, for example, gold, in the form of a huge balloon with a diameter of 200 meters, then its core will be just … a 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, gold atoms are located quite densely, so the distance between neighboring "nuts" on the scale adopted by us 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 magnitudes of mass and charge, growing in “steps” from one chemical element to another, were painfully striking. It was logical to assumethat there are certain particles with a fixed positive charge, from which the nuclei of all atoms are “collected”. How many positively charged nucleons are in the nucleus, this will be its charge.
Assumptions about the complex structure of the atomic nucleus were made back in the period of Mendeleev's construction of his periodic table of elements. However, the technical possibilities to experimentally confirm conjectures did not exist at that time. Only at the beginning of the 20th century, Ernest Rutherford made an experiment that confirmed the existence of the proton.
As a result of exposure to the substance by the radiation of radioactive metals, from time to time a particle appeared - a copy of the nucleus of a hydrogen atom. It had the same weight (1.67 ∙ 10-27 kg) and atomic charge +1.
Neutron
The conclusion about the need to search for another particle, in absentia called the neutron, came quickly. Since the question of 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 ordinal number of the element. Rutherford made an assumption about the existence of a proton twin with zero charge, but he failed to confirm his conjecture.
In general, nuclear scientists already had a good idea of what nucleons are and the quantitative composition of atomic nuclei. And the elusive particle, yet experimentally discovered by no one, was waiting in the wings. James Chadwick is considered to be its discoverer, who managed to isolate the "invisible" from the substance,subjecting it to bombardment with helium nuclei accelerated to ultra-high speeds (α-particles). The mass of the particle, as expected, turned out to be equal to the mass of the previously discovered proton. According to modern research, the neutron is slightly heavier.
A little more about the "bricks" of the atomic nucleus
Calculate how many nucleons in the nucleus of a chemical element or its isotope is easy. This requires two things: a periodic table and a calculator, although you can calculate in your mind. An example is the two common isotopes of uranium: 235 and 238. These numbers represent the atomic mass. The serial number of uranium is 92, it always denotes the charge of the nucleus.
As you know, nucleons in the nucleus of an atom can be either positively charged protons or neutrons of the same mass, but without a charge. Serial number 92 denotes the number in the nucleus of protons. The number of neutrons is calculated by simple subtraction:
- - uranium 235, number of neutrons=235 – 92=143;
- - uranium 238, number of neutrons=238 – 92=146.
And how many nucleons can be brought 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 bowels 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 matter, consisting of "pressed" neutrons, is extremely dense.
A star weighing in our Sun turns into a ballseveral tens of kilometers in diameter. A teaspoon of such "neutron porridge" could weigh several hundred tons on Earth.
