Final answer:
The sum of oxidation numbers in a polyatomic ion equals the ion's charge. This helps in balancing chemical equations and in maintaining charge conservation during reactions. Oxidation numbers adhere to trends based on elements' positions in the periodic table.
Step-by-step explanation:
The sum of the oxidation numbers in a polyatomic ion should equal the charge on the ion. This principle helps balance chemical equations and ensures that electron transfer processes are correctly represented.
For example, in the sulfate ion (SO42-), the oxygen atoms each have an oxidation number of -2, totalling -8 for all four oxygen atoms combined. Since the overall charge of the sulfate ion is 2-, the sulfur atom must have an oxidation number of +6 to balance the -8 from the oxygens, resulting in the overall 2- charge of the sulfate ion.
Remember, for neutral molecules, the sum of all oxidation numbers must equal 0. For polyatomic ions, this sum must equal the net charge of the ion. Oxidation numbers also follow certain trends, such as alkali metals having a +1 oxidation number and alkaline earth metals having a +2 value.