What's the charge of Fe2S3 ?

Question

melissa_something · Answer

$$Fe _{2}S _{3}$$

jfraser · Answer

$Fe_2S_3$ $has$ no net charge, the formula is $neutral$

melissa_something · Answer

Oh, but how do you know? I'm beating myself up trying to find the charge of Fe

jfraser · Answer

you're looking at 2 different things. The charge of a $molecule$ is always neutral. the charges of the $ions$ that make up the formula is what you're really asking for, right?

melissa_something · Answer

It just asks me what the charge of it is, then says +2, -2, +3, etc

melissa_something · Answer

I don't know :(

jfraser · Answer

because transition metals usually have more than one option for their charge, it's helpful to look at the ion they are $paired \space to$ to find the opposite charge, since they must add up to zero.

jfraser · Answer

in this formula, the iron is paired with sulfur.

what kind of ion does sulfur form?

melissa_something · Answer

I thought I had a clue but my brain just farted, would it be cation? Idk how to tell

jfraser · Answer

it's listed second in the formula, meaning the sulfur will have a negative charge.

sulfur is also in the same family as $oxygen$, so if you know the charge that oxygen forms, sulfur will be the same

melissa_something · Answer

The charge would be 6, right?

melissa_something · Answer

Does the element listed second in a formula always have a negative charge?

jfraser · Answer

6 is the number of valence electrons sulfur has, not its charge.

jfraser · Answer

yes, the non-metal in an ionic compound (which is always listed second) will always have a negative charge

melissa_something · Answer

Of course... then how do you tell?

melissa_something · Answer

Okay that helps

jfraser · Answer

do you know the much about valence electrons, or atomic orbitals & quantum numbers?

melissa_something · Answer

Yes, I always seem to forget the simple stuff

jfraser · Answer

ok, then what's the "magic" number of valence electrons to make an atom happy?

melissa_something · Answer

The nearest one to the noble gas, no?

jfraser · Answer

yes, and how many valence electrons do the noble gases have?

melissa_something · Answer

8

jfraser · Answer

good

jfraser · Answer

so a sulfur atom has 6 valence electrons, it "wants" 8 to look just like argon and be "happy"

jfraser · Answer

how many electrons does the sulfur have to pick up to look just like argon?

melissa_something · Answer

Yeah :D

melissa_something · Answer

2!

jfraser · Answer

great, so picking up 2 valence electrons turns the sulfur $atom$, $S$, into the sulfide $ion$, $S^{-2}$

jfraser · Answer

the charge of a sulfide ion is -2

jfraser · Answer

in this formula, there are $three$ sulfide ions, right?

melissa_something · Answer

Yes there is

melissa_something · Answer

We multiply?

jfraser · Answer

since each sulfide ion has a charge of -2, and there are 3 of them, what's the $total$ negative charge?

melissa_something · Answer

-6!!!!

jfraser · Answer

exactly

melissa_something · Answer

Woah

jfraser · Answer

since the $total$ charge of the irons $MUST$ balance the charges from the sulfides, what must the $total$ positive charge be?

melissa_something · Answer

Positive 6

melissa_something · Answer

So we multiply by 3 right?

jfraser · Answer

so what we've got is basically this:

$Fe_2S_3$

$2*(+?) + 3*(-2) = 0$

melissa_something · Answer

Oh so yeah we have to multiply by three

jfraser · Answer

there's +6 of total positive charge.

that positive charge is going to be split evenly between the irons. 

there are 2 iron ions.

What is the charge on $each$ iron ion going to be?

melissa_something · Answer

3?

jfraser · Answer

it is a +3

melissa_something · Answer

Yes!

jfraser · Answer

the same basic rules apply to all ionic compounds. the total charge must be zero, so there must be enough positive and negative pieces to balance that charge

melissa_something · Answer

I see, but I think we're talking about two different things, the answer should be +3 :C

jfraser · Answer

we're actually talking about the exact same thing. You have to use the rules of ionic formulas to figure out what the charges of the partners are

melissa_something · Answer

Okay, I'll research it!!! It made me confused bc of the +3

jfraser · Answer

if the question is "what's the charge of the $iron$ in the $Fe_2S_3$", then the answer is certainly a +3

melissa_something · Answer

Oh... because Fe is the metal ion. I feel so bad. Duh!

whpalmer4 · Answer

And you'll sometimes see that written as iron(III) sulfide to indicate that the iron is in the +3 state.  

That compound is also known as pyrite or iron pyrite or fool's gold, the last because it makes shiny crystals that look a bit like gold.