How to determine the degree of oxidation

All chemicals consist of molecules that are the smallest particles. They are electrically neutral and consist of atoms that are bound by covalent bonds. The ability of atoms of chemical elements to form a certain number of bonds in molecules is called valence. In connection with the emergence and development of the theory of chemical bonds, this concept has undergone significant changes and currently does not have a clear scientific interpretation, it is used mainly for methodological purposes and is often identified with the degree of oxidation. If a molecule is the smallest particle of a substance, then the atom is the smallest indivisible particle of a chemical element. The atom is also an electrically neutral particle, in its center there is a nucleus consisting of positively charged protons, and around it is a cloud of electrons (negatively charged). Therefore, the positive charge of the nucleus is balanced by a negative electron charge. To understand how to determine the degree of oxidation and what it is, you need to consider the structure of molecules of specific substances.

In a molecule of hydrogen chloride (HCl) between hydrogen and chlorine, there is one common pair of electrons. The hydrogen atom has 1 proton and 1 electron. The chlorine atom has 17 protons and 17 electrons, one of the 7 electrons in the outer shell of the electron density has united with the electron of the hydrogen atom, thus forming an electron pair: H: Cl. In the H2S molecule, the sulfur atom formed two general pairs of electrons with both hydrogen atoms: H: S: H. How to determine the degree of oxidation of an element, for example, chlorine and hydrogen in a molecule of HCl and hydrogen and sulfur in a H2S molecule? Valence gives an idea of the number of bonds or electron pairs formed in the molecule, but does not indicate their displacement.

It is assumed that the electrons of atoms in the molecule are combined into electron pairs, which are shifted to the most electronegative atom. Hydrogen and chlorine in HCl are able to enter into one bond, which is shifted to the chlorine atom, since it is the most electronegative. Thus, in hydrogen, the degree of oxidation is plus 1, and for chlorine, minus 1. Each hydrogen atom in the H2S molecule comes into one bond with the sulfur atom, which in turn has two bonds. Both electron pairs in this case are shifted to the sulfur atom. Therefore, for hydrogen, the degree of oxidation is plus 1, and for the sulfur atom - minus 2. How to determine the degree of oxidation of a substance, for example, HCl, H2S, O2, N2, Na, Ag, Si? The degree of oxidation of a simple or complex substance is always 0, since the substance consists of molecules or atoms, and they are electrically neutral. Based on this, the degree of oxidation of the element in the molecule is found.

For example, with hypochlorous acid, one can consider how to determine the degree of oxidation for the Cl atom. In the HClO molecule, like in any other substance, hydrogen always (except for hydrides) is characterized by an oxidation state of plus 1, and oxygen is always oxidized minus 2 (except for barium peroxide and oxygen fluoride). Since the molecule itself does not have a charge, we can write the equation: (+1) + x + (-2) = 0. This equation must be solved: x = 0 - (+1) - (-2) = (+1) , Thus, it turns out that the degree of oxidation of Cl in the molecule of hypochlorous acid is equal to plus 1. This example shows how to determine the degree of oxidation of a specific element in any molecule. First of all, the known values of those elements whose valence or degree of oxidation do not change are placed.

Thus, the degree of oxidation is a conventional quantity (the formal charge of an atom in a molecule) used to write the reaction equations associated with the oxidation or reduction of various substances. This value is equal to the number of pairs of electrons that are completely shifted toward the electronegative chemical elements of the molecule. The degree of oxidation is recorded above the conventional designation of the atom. Such a record indicates how to determine the degree of oxidation of a particular element in a molecule of any substance. For example, the record (Na + 1Cl-1) should be understood that in the salt of the salt, the degree of sodium oxidation is plus 1 and that of chlorine minus 1, thus: (+1) + (-1) = 0. In the potassium permanganate molecule (K + 1Mn + 7O-24) for potassium plus 1, for manganese plus 7, for oxygen minus 2, that is: (+1) + (+7) + 2 • (-2) = 0. In the molecule of the acid nitric (H + 1N + 5O-23) for hydrogen plus 1, for nitrogen plus 5, for oxygen minus 2, and the molecule as a whole is electrically neutral: (+1) + (+5) + 3 • (-2) = 0. In a nitrogenous molecule Acid (H + 1N + 3O-22), for hydrogen plus 1, for nitrogen plus 3, for oxygen minus 2, since the charge of the molecule is zero, then: (+1) + (+3) + 2 • (-2) = 0. On the example of nitrogen, it can be seen that this atom can have different oxidation states in different substances from plus 5 to minus 3 (with an interval of one unit).