You have to balance the atoms first with their charges. Iron or Fe is a transition metal. Transition metals as a whole group do not have a specific charge. Iron has different charges but in this case, it’s charge is +3.
Oxygen has a charge of -2 since it is in column 16, shown in the table.
- Now you must balance the atomic charges. To do that, you want the charges of the iron and the oxygen to cancel. So, for iron, you multiply its charge of +3 by 2 to get +6 You are taking 2 atoms of iron(III) (or iron atoms with a charge of +3) so it is written as ##Fe_2##. For oxygen, you multiply -2 by 3 to get -6. You have 3 oxygen atoms with a charge of -2, so the answer is ##Fe_2O_3##. Check your work by adding up the charges. -6+6=0, which works since you get a net charge of 0.
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NOTE – When I say charge, each element has a certain number of (electrons in their outer shell). So, if you are in Group 1 (the alkali metals), you would have a +1 charge. – Your charge is based on columns or families (horizontal!). This is shown in the picture