The following article talks about the atom and its structure: how it was discovered, how the theory was developed in their minds and during experiments, thinkers and scientists. The quantum-mechanical model of the atom as the most modern today most fully describes its behavior and the particles that make up the composition. Read about her and her features below.
Atom concept
The chemically indivisible minimum part of a chemical element with a set of characteristic properties is an atom. It includes electrons and a nucleus, which, in turn, contains positively charged protons and uncharged neutrons. If it contains the same number of protons and electrons, then the atom itself will be electrically neutral. Otherwise, he has a charge: positive or negative. Then the atom is called an ion. Thus, their classification is carried out: a chemical element is determined by the number of protons, and its isotope by neutrons. Binding to each other on the basis of interatomic bonds, atoms form molecules.
A bit of history
For the first time, ancient Indian and ancient Greek philosophers spoke of atoms. And in the period of the seventeenth and eighteenth centuries, chemists confirmed the idea, experimentally proving that some substances can not be split into their constituent elements through chemical experiments. However, from the late nineteenth to the early twentieth centuries, physicists discovered subatomic particles, making it clear that the atom is not indivisible. In 1860, chemists formulated the concepts of atom and molecule, where the atom became the smallest particle of the element, which was part of both simple and complex substances.
Atom structure models
- Pieces of matter. Democritus believed that the properties of substances can be determined by mass, shape and other parameters that characterize atoms. For example, fire has sharp atoms, because of which it has the ability to burn; solids contain rough particles, due to which they adhere to each other very tightly; they are smooth in water, so it can flow. According to Democritus, even the human soul consists of atoms.
- Thomson models. The scientist considered the atom as a positively charged body, inside of which there are electrons. Rutherford refuted these models by conducting his famous experience.
- The early planetary models of Nagaoka. At the beginning of the twentieth century, Hantaro Nagaoka proposed atomic nucleus models similar to the planet Saturn. In them around the small nucleus, charged positively, electrons united in rings rotated. These versions, like the previous ones, turned out to be erroneous.
- Planetary models of Bohr-Rutherford. After conducting several experiments, Ernest Rutherford suggested that the atom is similar to the planetary system. In it, the electrons move in orbits around the nucleus, which is positively charged and located in the center. But classical electrodynamics contradicted this, because, through it, the electron, moving, emits electromagnetic waves, and therefore loses energy. Bohr introduced special postulates, according to which the electrons did not radiate energy, while being in some specific states. It turned out that classical mechanics was unable to describe these models of the structure of the atom. This subsequently led to the appearance of quantum mechanics, which allows explaining both this phenomenon and many others.
Quantum-mechanical model of the atom
This model is a development of the previous one. The quantum-mechanical model of an atom assumes that there are no charge neutrons and positively charged protons in the nucleus of an atom. Around it are negatively charged electrons. But in quantum mechanics, electrons do not move along predetermined defined paths. So, in 1927, W. Heisenberg voiced the principle of uncertainty, which makes it impossible to accurately determine the coordinate of a particle and its velocity or momentum.
The chemical properties of electrons are determined by their shell. In the periodic table, atoms are arranged according to the electric charges of the nuclei (we are talking about the number of protons), while neutrons do not affect the chemical properties. The quantum-mechanical model of the atom proved that its bulk is in the nucleus, while the fraction of electrons remains insignificant. It is measured in atomic units of mass, which is equal to 1/12 of the mass of the carbon isotope atom of C12.
Wave function and orbital
According to the principle of W. Heisentberg, one cannot speak with absolute certainty that an electron that has a certain speed is located at any particular point in space. In order to describe the properties of electrons, use the psi wave function.
The probability of detecting a particle at a specific time is directly proportional to the square of its module, which is calculated for a specific time. Psi squared is called the probability density, which characterizes the electrons around the nucleus in the form of an electron cloud. The larger it is, the more likely the electron in a certain space of the atom will be higher.
For a better understanding, you can imagine overlapping photographs one on top of another, where the electron’s position is fixed at different points in time. In the place where there will be more points and the cloud will become the most dense, and the highest probability of finding an electron.
It is calculated, for example, that the quantum-mechanical model of the hydrogen atom includes the highest density of the electron cloud located at a distance of 0.053 nanometers from the nucleus.
The orbit from classical mechanics is replaced in a quantum electron cloud. The wave function of the psi electron is called the orbital, which is characterized by the shape and energy of the electron cloud in space. As applied to an atom, we mean the space around the nucleus in which the presence of an electron is most probable.
Impossible is possible?
Like the whole theory, the quantum-mechanical model of the structure of the atom has truly revolutionized the scientific world and among ordinary people. Indeed, to this day it is difficult to imagine that one and the same particle at one and the same moment in time can be simultaneously not in one, but in different places! To protect the established structures, they say that events occur in the microworld that are unthinkable and are not such in the macrocosm. But is it really so? Or are people simply afraid to even admit the possibility that “a drop is like an ocean and an ocean is a drop”?