## Writing formulas for compounds [ENDORSED]

Angelica Gomez 1A
Posts: 6
Joined: Fri Jun 17, 2016 11:28 am

### Writing formulas for compounds

"Write the complete Lewis structure for each of the following compounds: a) Ammonium chloride b) potassium phosphide c) sodium hypochlorite."
How do we figure out the subscript for each element when we are writing the formula for the compound?

Chem_Mod
Posts: 17949
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 406 times

### Re: Writing formulas for compounds  [ENDORSED]

Because these are compounds and not ions, each of these compounds has an overall charge of zero. Only ions have charges. Therefore, to figure out the subscript, we must first determine the charge of the individual ions in each compound.

a) ammonium chloride: the formula for the ammonium ion is NH4+; the formula for the chloride ion is Cl-. Because you have a +1 and a -1 charge, it already adds to zero, so you only need one ion each. The formula for ammonium chloride is NH4Cl

b) potassium phosphide: the formula for the potassium ion is K+; the formula for the phosphide ion is P-3. You have have a +1 and a -3 charge. In order to get them to add to zero, you need three of the +1 potassium ions. Thus, the subscript for potassium is 3. The formula for potassium phosphide is K3P

c) sodium hypochlorite: the formula for the sodium ion is Na+; the formula for the hypochlorite is ClO-. Because you have a +1 and a -1 charge, it already adds to zero, so you only need one ion each. The formula for sodium hypochlorite is NaClO

derek1d
Posts: 19
Joined: Wed Jun 28, 2017 3:00 am

### Re: Writing formulas for compounds

I am working on the same problem and while the explanation helps I still am confused on whether or not we are expected to know the chemical formulas for these salts?

I understand how we deduce the subscripts, but are we supposed to know that for example, ammonium ion is NHsub4? Or where do we get that information?

Prior to this problem I thought Ammonia was NHsub3 so I am just confused as to where we get this from and what do we used to derive the chemical formula for other questions that provide only the name?