Molecular Formula to Ionic Compounds

[Caitlin_Murphy_3C]

In Friday's lecture, when we did the example of how to draw the lewis structure of polyatomic species, Dr. Lavelle gave first the molecular formula of ammonium sulfate, then split this molecular formula into two ionic compounds ( (NH4)2SO4 -> NH4+ and SO42- ). In problems like this, do we need to know how to split up a molecular formula into its ionic compounds, or will it be given? How do you split molecular formulas into their respective ionic compounds?

[Nicole Elhosni 2I]

NH4+ and SO42- are both polyatomic ions, ammonium and sulfate. In my highschool chemistry, we had to memorize a list of polyatomic ions, but I am not sure for this class. But you can figure out how the entire molecule, (NH4)2SO4 breaks down into ions without knowing the polyatomic ions before! (NH4) is in parenthesis because the 2 charge, which comes from the SO42-, applies to the whole polyatomic ion. So even if you didn't know about NH4+ prior to this, you could deduce it is as a polyatomic ion because the charge from the SO42- applies to all of NH4+ (not just an N, or an H). The same goes for SO42-, but the charge isn't written because NH4+ only has a charge of one.