Question

predict the formula for this ionic compound nickel(II) iodide.......could you show how you did it as well please

Answer 1

So in the name Nickel(II) we can tell that it's going to be Ni+2 while for Iodide ion we don't know for sure unless we check the periodic table or remembered it. So if you look at this picture you can tell that all the atoms falling in areas 1-3 form + charges by losing electrons and becoming cations. 5-7 gain electrons and become anions. 4 either loses or gains 4 electrons and the atoms in column 8 have 8 electrons, which is the most stable electron configuration.

So what happens is Iodine gains an electron since it falls in category 7 so that it has 8 electrons. However, this extra negative charge from the electron it picked up gave it a -1 charge.

So far we have this right?
That shows that we have 2 positive charges on the Nickel and 1 negative charge on the Iodide ions. So they attract each other until their charges cancel each others out. A +1 and -1 charge would give you a 0 charge, or stable formula, right? So how many of each do you need to cancel each other out?
Just like that, you can tell that your formula is NiI2