An ionic lattice is a repeating arrangement in three dimensions for ionic compounds like NaCl. We can't draw diagrams on this forum but here is a link.
https://www.google.com/search?q=ionic+lattice&tbm=isch&tbo=u&source=univ&sa=X&ei=t2iYVc-rOsyMNu2dgig&ved=0CB4QsAQ&biw=1014&bih=600
Here is another link that talks more about how the arrangements but the pictures, in my opinion, are not as good.
https://www.wou.edu/las/physci/ch412/lattice.html
On the Roman numerals thing you have the right idea but a little off base. The Roman numerals are used in the NAME of the substance, not in the formula. Your explanation is ok because you don't differentiate between formula or name but the idea is this.
If you want to talk about copper sulfate, you write it copper(II) sulfate so you will know the valence of Cu is +2 and not +1. You don't need that for the formula of CuSO4 because you know SO4 is -2 so Cu MUST be +2. ZnSO4 is named. The same is true for iron(II) and iron(III) compounds such as FeCl2 and FeCl3. It isn't necessary, as you point out for ZnSO4 since Zn doesn't have variable valences (oxidation states). In summary, CuSO4 is named copper(II) sulfate and ZnSO4 is names zinc sulfate. Personally, I don't object if someone names ZnSO4 as zinc(II) sulfate but I think purists object.
These are all review questions for my summer assignment.
Do not know:
!) Explain what an ionic lattice is and include a diagram.
2)Draw a diagram to show how Na and CL2 combine to form NaCl
Unsure:
!)Select two compounds and explain when Roman numerals are used in the name of an ionic compound and when they are not used.
Roman Numerals are used only when the metal has more than one charge. For example, Cu can have either a +2 or +1 charge, while Zn has one charge, +2. In Cu(II)SO4, the roman numerals are used so scientists can see that when Cu and SO4 combine, Cu becomes a +2 not a +1. But for ZnS04, the roman numerals are not necessary since Zn only has one charge.
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For the diagram of NaCl (I didn't look at the second link if that would help me with this question, yet) would me drawing what Na and Cl look like in the arrangement of their atoms before and after they combine be good enough?
No, I don't think that would show the 3-D arrangement. I think I want to draw Na ion and Cl and them repeating in 3D as in the first link I gave you.
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