So to complete this chart, we have to remember that compounds want to retain a neutral charge. Therefore, we need to compensate a difference in charge by adding more of that element in the compound.
So let's take [tex] Au^{3+} [/tex] and [tex] CN^{-} [/tex]. Since cyanide has a -1 charge and gold has a +3 charge, we are going to need 3 moles of cyanide per mole of gold. So then the neutral compound of gold cyanide would be: [tex] AuCN_{3} [/tex]
Then we have [tex] K^{+} [/tex] and [tex] CO_{3}^{2-} [/tex]. In order to compensate for the +1 charge on the potassium being one less than the carbonate's -2 charge, we are going to need two moles of potassium for every carbonate. So then the compound will be: [tex] K_{2}CO_{3} [/tex]
And lastly we have [tex] Au^{3+} [/tex] and [tex] CO_{3}^{2-} [/tex]. Since these charges don't balance easily, we can then find the lowest common multiple - in this case it will be 6. So to get a +6 charge, we will need 2 moles of gold, and to get a -6 charge, we will need 3 moles of carbonate. Then we put it into the compound formula: [tex] Au_{2}(CO_{3})_{3} [/tex]
