The oxidation state is the conditional charge of an atom of an element in a molecule. This concept is fundamental in inorganic chemistry, without its understanding 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 the degree of oxidation 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 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 supply and form the energy level or electron layer. Electrons at the external energy level are not too strongly connected with the nucleus, so they can participate in chemical reactions. Elements that have from one to four electrons at the external level, in chemical reactions, as a rule, give up electrons, and those that have five to seven electrons take it.
There are also chemical elements called inert gases, in which the external energy level contains eight electrons - the maximum possible amount. They practically do not enter into chemical reactions. So, any atom seeks to "supplement" its outer electronic layer with the necessary eight electrons. Where to get the missing? Other atoms.
In the
process of a chemical reaction, an element with a greater electronegativity "picks up" an electron from an element with a lower electronegativity. The electronegativity of a chemical element depends on the number of electrons at the valence level and the strength of their attraction to the nucleus. For an element that has taken away the electrons, the total negative charge becomes greater than the positive charge of the nucleus, and for the one who has given up the electron - vice versa. For example, in the
sulfur oxide compound SO, oxygen having a large electronegativity takes away 2 electrons from sulfur and acquires a negative charge, while sulfur, left without two electrons, receives a positive charge. In this case, the degree of oxidation of oxygen is equal to the degree of oxidation of sulfur taken with the opposite sign. The oxidation state is recorded in the upper right corner of the chemical element. In our example, it looks like this: S
+2 O
-2 .
The example described above is quite simplified. In fact, the external electrons of one atom never completely transfer to another, they only become "common", therefore, the oxidation state of elements is always less than indicated in textbooks.
But to simplify the understanding of chemical processes, this fact is neglected.