[Professor 0110]

I was just wondering if anyone could explain to me how ionic bonding works as it relates to the formation of Iron Chloride, in minute detail if possible. For example, from which of the elements does the transfer of electrons occur and why is hydrogen gas released as a result of this chemical change?

Here is the chemical formula for the creation of Iron (II) Chloride:

Fe + HCL -> FeCl2 + H2

If someone could explain the above equation to me as well as answer my previous question about the ionic bonding occurring, that would be great. (I also realize the two questions are essentially interrelated).

Oh, and one more thing: is Iron (II) Chloride only able to be formed when iron and hydrochloric acid are heated over a flame? What if the two elements are merely mixed together in a test tube? Is a compound still formed?

Thank you for any help you're able to provide.

[Angelant99]

Fe + 2HCl -> FeCl₂ + H₂

A look into the reaction:

Iron is the better reducing agent between Iron and Hydrochloric acid, so it gives up electrons (gets oxidised) first via this equation -

Fe(s) => Fe²⁺(aq) + 2e^-

So every reacting iron atom forms 2 electrons and an Fe²⁺ ion.

The 2 molecules of HCl which are taking part (i balanced your formula above ) will then receive these 2 electrons. (Chloride ions are spectator ions in this reaction - they're not actually in the reaction, per se. So we could just leave them out.)

And what seems to happen is that the 2H⁺ ions from 2HCl will each gain an electron and bond together to form H₂(g)  via this equation:

2H⁺(aq) + 2e^- ==> H₂(g)

If we leave out the spectator ions completely, what's really happening is this:

Fe(s) + 2H⁺(aq) ==> H₂(g) + Fe²⁺(aq)


A little on ionic bonding:

Ionic compounds form regular structures called giant ionic lattices which is basically a complex 3D shape made up of alternating positive then negative ions, holding each other together by electrostatic attraction. Sodium chloride's always a nice example - If you look at a sodium ion away from the edge of the shape, every positive sodium ion is joined to 6 adjacent negatively charged chloride ions.
Standard lattice enthalpy values will tell you which lattice has the strongest bonding in it - the more negative the value is, the more energy is needed to break it.

(MgO for example, has a stronger lattice than NaCl)

In the case of Iron(ii) chloride, if you look at this link on wiki: http://en.wikipedia.org/wiki/Iron%28II%29_chloride   you'll see, along the right hand side, a perfect example of just how much higher the melting and boiling points are for ionic compounds, compared with covalent. The pic at the top's not that bad either - beautiful isn't it? 


I'd imagine that the reaction would still take place without heating, but that heating merely speeds the process along - it may be quite a slow reaction, but a reaction that happens nonetheless.


Phew  Hope that was helpful. I'd suggest you do a little reading on ionic bonding and have a google around for ionic lattices, they're rather pretty.

[Professor 0110]

That reply was nothing short of awesome, Angleant99! 

It made everything much, much clearer!

Thanks!!!!!

[Angelant99]

Excellent!    Glad i was useful - i'll answer your other question from your personal message here too 

I assume you mean iron(ii) sulphide, FeS and not iron (iii) sulphide, Fe₂S₃?  (Don't let the 'ph' i put in 'sulphide' bother you btw it's just what i've been taught to do, here in the UK lol)

For starters, there's a nice pic here: http://en.wikipedia.org/wiki/Iron%28II%29_sulfide  oooh and apparently powdered iron(ii) sulphide is pyrophoric - it bursts into flames readily with the air lol

Umm..in the last question you asked me, you gave me a formula to work with...do you have one for this question? 

Perhaps  Iron + Hydrogen sulphide -> Iron sulphide + Hydrogen? I don't know if that works - i was much more familiar with the equation you gave last time lol
Well, there is this...S₈(s) + 8Fe(s) → 8FeS(s)

So ok, i'll use that. lol

Iron is once again the better reducing agent between the two reagents, so each of the eight atoms gives up 2 electrons (gets oxidised) to form eight Fe²⁺ ions. This frees 8 x 2 =16 electrons.

8Fe(s) => 8Fe²⁺(aq) + 16e^-

Sulphur is a group 6 element - so it has 6 electrons in its outermost shell and gains 2 to complete the shell, when it becomes an ion. (S^2-)
So each of the 8 sulphur atoms in S₈ then gain 2 electrons and form 8S^2- ions.

S₈(s) + 16e^- => 8S^2-(aq)

Overall:
 
S₈(s) + 8Fe(s) => 8FeS(s)

I can also tell you that both Iron(ii) chloride and Iron(ii) Sulphide have a hexagonal crystal system.



Let me know if there's anything else i can do to help