how to write formulas or name compounds?

[ukfan879]

I do not know how to do this if it get to indepth.
examples of problems I am doing for homework are:
1.  Ni(HSO4)2 * H20

An example on the other way around are:

1.Zinc iodide monohydrate
and i have to put this in a formula

[kyle1990]

Are you sure that is Ni(HSO4)2 and not NiSO4?

For the next problem, break it down piece by piece.

Zinc has the symbol Zn, so that has to be somewhere in the formula.

Iodide- indicates that Iodine is in the formula (I). The -ide ending is important. This generally means that there are only TWO elements bonded together, in this case it's zinc and iodine. Here are some other simple examples of that

NaCl - sodium chloride
NaH  - sodium hydride

Take home lesson: two atoms= -ide ending

Now you need to figure out how many atoms of each there are. This is where you need to know the charges on the ions.

Zinc ions have a +2 charge. Iodide ions have a -1 charge. So you need two iodide ions to cancel out a zinc ion. Simply cross the charges.
So the formula becomes ZnI₂

Almost done. Don't forget about the monohydrate. This is just a fancy way of saying one water is attached (mono=1 hydrate=H2O)

Hydrates are not chemically bonded to the atoms in the compound, so they are just represented as a * to indicate that they are attached but not chemically bonded.

So the overall formula becomes ZnI₂*H₂O

It may seem like a lot of steps, but practice is key and it will become much easier once you get the hang of it.

[valdorod]

for anions with a negative 2 or negative 3 charge, you can usually form extra ions by attaching one hydrogen to the negative 2 and one or 2 hydrogens to the negative 3.  These ions are found in many salts.  The prefix bi is usually added to the name of the ion for one hydrogen as a common name.  Formally the word hydrogen is appended to the beginning of the ion.

examples

CO₃^2- = carbonate

HCO₃^1- = bicarbonate or hydrogen carbonate


SO₄^2- = sulfate

HSO₄^1- = bisulfate or hydrogen sulfate


SO₃^2- = sulfite

HSO₃^1- = bisulfite or hydrogen sulfite


on the -ide endings, two important exceptions that you will surely encounter where it does not mean two atoms.

hydroxide (OH^-) and
cyanide (CN^-)