Determine the oxidation number for the indicated element in...

Determine the oxidation number for the indicated element in each of the following substances: (a) $\mathrm{S}$ in $\mathrm{SO}_{2}$ (b) $\mathrm{C}$ in $\mathrm{COCl}_{2},(\mathrm{c}) \mathrm{Mn}$ in $\mathrm{MnO}_{4}^{-},(\mathrm{d}) \mathrm{Br}$ in $\mathrm{HBrO},(\mathrm{e}) \mathrm{As}$ in $\mathrm{As}_{4}$, (f) $\mathrm{O}$ in $\mathrm{K}_{2} \mathrm{O}_{2}$.

Determine the oxidation number for the indicated element in each of the following substances: (a) $\mathrm{S}$ in $\mathrm{SO}_{2}$ (b) $\mathrm{C}$ in $\mathrm{COCl}_{2},(\mathrm{c}) \mathrm{Mn}$ in $\mathrm{MnO}_{4}^{-},(\mathrm{d}) \mathrm{Br}$ in $\mathrm{HBrO},(\mathrm{e}) \mathrm{As}$
in $\mathrm{As}_{4}$, (f) $\mathrm{O}$ in $\mathrm{K}_{2} \mathrm{O}_{2}$.

Key Concepts

Oxidation Number

The oxidation number is a theoretical charge assigned to an atom in a compound, assuming that all bonds between different elements are completely ionic. It is a useful bookkeeping tool to track electrons during chemical reactions, particularly redox processes.

Rules for Assigning Oxidation Numbers

A set of standard rules is used to determine oxidation numbers. These rules include assigning 0 to atoms in their elemental state, assigning known values such as -2 for oxygen (with notable exceptions) and +1 for hydrogen when bonded to non-metals, and ensuring that the sum of oxidation numbers in a neutral molecule is zero or equals the net charge in an ionic species.

Summing Oxidation Numbers in Compounds and Ions

When determining oxidation numbers, it is essential that the total oxidation number in a neutral molecule adds up to zero, and in the case of polyatomic ions, the sum must equal the ion’s charge. This principle helps to balance and distribute oxidation numbers among the atoms in complex structures.

Exceptions and Special Cases in Oxidation States

There are exceptions to the general rules, such as in peroxides where oxygen typically has an oxidation number of -1 rather than -2, or in compounds containing fluorine where it always has an oxidation number of -1. Recognizing these exceptions is crucial for correctly assigning oxidation numbers in various chemical contexts.

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