A modern person constantly hears phrases that contain derivatives of the word "atom". It's energy, power station, bomb. Someone takes it for granted, and some ask: "What is an atom?".
What does this word mean?
It has ancient Greek roots. It comes from "atomos", which in literal translation means "uncut".
Someone who is already a little familiar with the physics of the atom will be indignant: "How" uncut "? It also consists of some particles! "The thing is that the name appeared when scientists did not yet know that atoms are not the smallest particles.
After an experimental proof of this fact, it was decided not to change the usual name. And in 1860 the "atom" was called the tiniest particle, which has all the properties of the chemical element to which it refers.
What is more than an atom and less than it?
A molecule is always greater. It is formed from several atoms and is the smallest particle of matter.
But smaller - elementary particles. For example, electrons and protons, neutrons and quarks. There are a lot of them.
Already a lot of things about him said. But until now it is still not very clear what an atom is.
What he really is?
The question of how to represent the model of an atom has long occupied scientists. Today, the one that was proposed by E. Rutherford and finalized by N. Bor. On it, the atom is divided into two parts: the core and the electronic cloud.
Most of the mass of the atom is concentrated in its center. The core consists of neutrons and protons. And the electrons in the atom are located at a sufficiently large distance from the center. It turns out something similar to the solar system. In the center, like the Sun, the core, and around it, the electrons rotate along their orbitals, like planets. That's why the model is often called planetary.
It is interesting that the nucleus and electrons occupy a very small space in comparison with the overall dimensions of the atom. It turns out that the center is a small nucleus. Then emptiness. Very large emptiness. And then a narrow strip of small electrons.
To such a model of atoms, scientists did not come immediately. Before that, a lot of assumptions were put forward, which were refuted by experiments.
One such idea was the representation of an atom in the form of a solid body, which has a positive charge. And the electrons in the atom were supposed to be placed throughout this body. This idea was put forward by J. Thomson. His model of the atom was also called "Pudding with raisins". Very much the model reminded this dish.
But it was untenable, because it could not explain some properties of the atom. Therefore, it was rejected.
Japanese scientist H. Nagaoka on the question, what is an atom, proposed such a model. In his opinion, this particle has a remote resemblance to the planet Saturn. At the center of the nucleus, and the electrons revolve around it in orbits connected in a ring. Despite the fact that the model was not adopted, some of its provisions were used in the planetary scheme.
About numbers associated with an atom
First about physical quantities. The total charge of the atom is always zero. This is due to the fact that the number of electrons and protons in it is the same. And their charge is the same in magnitude and has opposite signs.
Often there are situations when an atom loses electrons or, on the contrary, attracts extra ones. In such situations, it is said that it has become an ion. And its charge depends on what happened to the electrons. If their number is less, the ion charge is positive. When the electrons are greater than the prescribed one, the ion becomes negative.
Now about chemistry. This science, like no other, gives the most understanding of what an atom is. After all, even the main table, which is studied in it, is based on the fact that the atoms are located in it in a certain order. It's about the periodic table.
In it, each element is assigned a certain number, which is related to the number of protons in the nucleus. Usually it is denoted by the letter z.
The next value is the mass number. It is equal to the sum of the protons and neutrons in the nucleus of the atom. Its designation is taken by the letter A.
The two indicated numbers are related to each other by the following equality:
Here N is the number of neutrons in the atomic nucleus.
Another important quantity is the mass of the atom. To measure it a special quantity is introduced. It is shortened:amu. And it is read as an atomic unit of mass. Proceeding from this unit, three particles, of which all the atoms of the universe are composed, have masses: