How to determine the degree of oxidation?
The degree of oxidation is the conditional charge of an atom in a molecule, it receives an atom as a result of the complete adoption of electrons, it is calculated from the assumption that all bonds are ionic in nature. How to determine the degree of oxidation?
Determination of the degree of oxidation
There are charged particles of ions, the positive charge of which is equal to the number of electrons obtained from a single atom. The negative charge of an ion equals the number of electrons accepted by one atom of a chemical element. For example, the record of such an element as Ca2 + means that the atoms of the elements have lost one, two or three elements. To find the composition of ionic compounds and molecular compounds, we need to know how to determine the degree of oxidation of elements. Oxidation rates are negative, positive and zero. If we take into account the number of atoms, then the algebraic degree of oxidation in the molecule is zero.
To determine the degree of oxidation of the element must be guided by certain knowledge. For example, in metal compounds, the oxidation degree is positive.And the highest oxidation state corresponds to the group number of the periodic system, where the element is located. In metals, oxidation states can be positive and negative. This will depend on the factor of exactly how the atom is connected to the metal. For example, if connected to a metal atom, then the degree will be negative; if connected to a non-metal, then the degree will be positive.
The negative highest degree of metal oxidation can be determined by subtracting from the figure eight the number of the group where the necessary element is located. As a rule, it is equal to the number of electrons on the outer layer. The number of these electrons also corresponds to the group number.
How to calculate the degree of oxidation
In most cases, the degree of oxidation of an atom of a particular element does not coincide with the number of bonds that it forms, that is, it is not equal to the valence of this element. Clearly this can be seen on the example of organic compounds.
Let me remind you that the valence of carbon in organic compounds is 4 (that is, it forms 4 bonds), but the degree of carbon oxidation, for example, in methanol CH 3 OH is -2, in CO 2 +4, in CH4 -4, in formic acid HCOOH + 2Valence is measured by the number of covalent chemical bonds, including those that have arisen by the donor-acceptor mechanism.
When determining the degree of oxidation of atoms in molecules, an electronegative atom, when one electron pair is displaced in its direction, acquires a charge of -1, but if two electron pairs, then -2 will be a charge. The degree of oxidation is not affected by the bond between the same atoms. For example:
- The bond of C-C atoms is equal to their zero oxidation state.
- C-H bond - here, carbon as the most electronegative atom will correspond to charge -1.
- The C-O bond of carbon, as less electronegative, will be +1.
Examples of determining the degree of oxidation
- In a molecule like CH 3Cl there are three C-HC bonds). Thus, the degree of oxidation of the carbon atom in this compound will be equal to: -3 + 1 = -2.
- Find the degree of oxidation of carbon atoms in the acetaldehyde molecule Cˉ³H3-C¹O-H. In this compound, three C – H bonds will give a total charge on the C atom, which is (Cº + 3e → Cˉ³) -3. The double bond C = O (here oxygen will take electrons from the carbon atom, because oxygen is more electronegative) gives a charge on the C atom, it is +2 (Cº-2e → C²), the same bond CH charge -1, which means the total the charge on the C atom is: (2-1 = 1) +1.
- Now we find the degree of oxidation in the ethanol molecule: Cˉ³H-Cˉ¹H2-OH. Here three C – H bonds will give the total charge on the C atom, it is equal to (Cº + 3e → Cˉ³) -3. Two C-H bonds will give a charge on the C atom, which will be equal to -2, while the C → O bond will give a charge of +1, which means the total charge on the C atom: (-2 + 1 = -1) -1.
Now you know how to determine the degree of oxidation of the element. If you have at least a basic knowledge of chemistry, then this task will not be a problem for you.