Write the chemical formula for the following compounds?

Write the formula for each of the following ionic compounds?

• Answer:

  The Roman Numerals mean the overall charge that element is contributing, because transition metals can have different charges. a) Tin contributes a +4 charge. There must be no overall charge difference, so you ask yourself how many oxygen atoms are needed to achieve this, bearing in mind that Oxygen's charge is -2. Hence Tin(IV) Oxide is SnO2. Apply this process to the rest and: b) Fe is contributing +3. S contributes -2. This does not go into 3 cleanly, so you scale up both atoms until it does. The lowest value you can have no overall charge difference is +6. So the formula is Fe2S3 (Because 2 x 3 = 6 and 3 x -2 = -6) c) Applying the same rules again, PbS2. d) CrI3, because of -1 charge per iodide atom. e) Li3N, as Nitrogen's in group 5, but in this case the charge has to be -3, hence the 3 Lithiums balancing it out. Sometimes you need to figure out the correct charge if not stated. f) Gold must just be multiplied up by 2 to balance the oxygen, so Au2O. Hope this helps!