The oxidation state is the conditional charge of an atom of an element in a molecule. This concept is fundamental in inorganic chemistry, without understanding it it is impossible to imagine the processes of redox reactions, types of bonds in molecules, chemical and physical properties of elements. In order to understand what an oxidation state is, you first need to figure out what the atom itself consists of and how it behaves when interacting with its own kind.
As you know, an atom consists of protons, neutrons and electrons. Protons and electrons, also called nucleons, form a positively charged nucleus, negative electrons revolve around it. The positive charge of the nucleus is balanced by the total negative charge of the electrons. Therefore, the atom is neutral.
Each electron has a certain level of energy, which determines the proximity of its location to the nucleus: the closer to the nucleus, the less energy. They are arranged in layers. The electrons of one layer have almost the same energy reserve and form an energy level or an electronic layer. The electrons in the outer energy level are not strongly bonded to the nucleus, so they can participate in chemical reactions. Elements having at the outer level fromone to four electrons, in chemical reactions, as a rule, donate electrons, and those that have five to seven electrons accept.
There are also chemical elements called inert gases, in which the outer energy level contains eight electrons - the maximum possible number. They practically do not enter into chemical reactions. So, any atom tends to “complete” its outer electron layer up to the required eight electrons. Where can I get the missing ones? Other atoms.
During a chemical reaction, an element with a higher electronegativity "takes" an electron from an element with a lower electronegativity. The electronegativity of a chemical element depends on the number of electrons in the valence level and the strength of their attraction to the nucleus. For an element that has taken electrons, the total negative charge becomes greater than the positive charge of the nucleus, and for an element that has given away an electron, vice versa. For example, in a compound of sulfur oxide SO, oxygen, which has a high electronegativity, takes 2 electrons from sulfur and acquires a negative charge, while sulfur, left without two electrons, receives a positive charge. In this case, the oxidation state of oxygen is equal to the oxidation state of sulfur, taken with the opposite sign. The oxidation state is written in the upper right corner of the chemical element. In our example, it looks like this: S+2O-2.
The above example is rather simplified. In fact, the outer electronsone atom is never completely transferred to another, they only become "common", therefore, the oxidation states of the elements are always less than indicated in textbooks.
But to simplify the understanding of chemical processes, this fact is neglected.
