What happens to the atoms of elements during chemical reactions? What are the properties of the elements? One answer can be given to both of these questions: the reason lies in the structure of the external energy level of the atom. In our article, we will consider the electronic structure of atoms of metals and non-metals and find out the relationship between the structure of the outer level and the properties of elements.
Special properties of electrons
When a chemical reaction occurs between the molecules of two or more reagents, changes occur in the structure of the electron shells of atoms, while their nuclei remain unchanged. First, let's get acquainted with the characteristics of electrons located at the most distant levels of the atom from the nucleus. Negatively charged particles are arranged in layers at a certain distance from the nucleus and from each other. The space around the nucleus where electrons are most likely to be foundcalled an electron orbital. About 90% of the negatively charged electron cloud is condensed in it. The electron itself in the atom exhibits the property of duality, it can simultaneously behave both as a particle and as a wave.
Rules for filling the electron shell of an atom
The number of energy levels where the particles are located is equal to the number of the period where the element is located. What does the electronic composition indicate? It turned out that the number of electrons in the outer energy level for s- and p-elements of the main subgroups of small and large periods corresponds to the group number. For example, lithium atoms of the first group, which have two layers, have one electron in the outer shell. Sulfur atoms contain six electrons at the last energy level, since the element is located in the main subgroup of the sixth group, etc. If we are talking about d-elements, then the following rule exists for them: the number of external negative particles is 1 (for chromium and copper) or 2. This is explained by the fact that as the charge of the nucleus of atoms increases, the internal d-sublevel is first filled and the external energy levels remain unchanged.
Why do the properties of elements of small periods change?
In the periodic system, periods 1, 2, 3 and 7 are considered small. A smooth change in the properties of elements as nuclear charges increase, starting from active metals and ending with inert gases, is explained by a gradual increase in the number of electrons at the external level. The first elements in such periods are those whose atoms have only one ortwo electrons that can easily break away from the nucleus. In this case, a positively charged metal ion is formed.
Amphoteric elements, such as aluminum or zinc, fill their external energy levels with a small amount of electrons (1 for zinc, 3 for aluminum). Depending on the conditions of the chemical reaction, they can exhibit both the properties of metals and non-metals. Non-metallic elements of small periods contain from 4 to 7 negative particles on the outer shells of their atoms and complete it to an octet, attracting electrons from other atoms. For example, a non-metal with the highest electronegativity index - fluorine, has 7 electrons on the last layer and always takes one electron not only from metals, but also from active non-metallic elements: oxygen, chlorine, nitrogen. Small periods end, as well as large ones, with inert gases, whose monatomic molecules have outer energy levels completely completed up to 8 electrons.
Features of the structure of atoms of large periods
Even rows of 4, 5, and 6 periods consist of elements whose outer shells can hold only one or two electrons. As we said earlier, they fill the d- or f- sublevels of the penultimate layer with electrons. Usually these are typical metals. Their physical and chemical properties change very slowly. Odd rows contain such elements, in which the external energy levels are filled with electrons according to the following scheme: metals - amphoteric element - non-metals - inert gas. We have already observed its manifestation in all small periods. For example, in an odd series of 4 periods, copper is a metal, zinc is an amphoterene, then from gallium to bromine, non-metallic properties are enhanced. The period ends with krypton, the atoms of which have a completely completed electron shell.
How to explain the division of elements into groups?
Each group - and there are eight of them in the short form of the table, is also divided into subgroups, called main and secondary. This classification reflects the different positions of electrons on the external energy level of the atoms of elements. It turned out that the elements of the main subgroups, for example, lithium, sodium, potassium, rubidium and cesium, the last electron is located on the s-sublevel. Elements of group 7 of the main subgroup (halogens) fill their p-sublevel with negative particles.
For representatives of secondary subgroups, such as chromium, molybdenum, tungsten, filling the d-sublevel with electrons will be typical. And for the elements included in the families of lanthanides and actinides, the accumulation of negative charges occurs at the f-sublevel of the penultimate energy level. Moreover, the group number, as a rule, coincides with the number of electrons capable of forming chemical bonds.
In our article, we found out what structure the external energy levels of atoms of chemical elements have, and determined their role in interatomic interactions.
