[Serring101]

I recently had a chem test with a question that asked to name FeCl₃

Now we all know that this is iron (III) chloride (naming with stock system)

But I put iron (III) trichloride because iron and chlorine make a covalent bond.

3.0 (Electronegativity of Cl) - 1.8 (Electronegativity of Fe) = 1.2

1.2<1.7 therefore it is a polar covalent bond.

So i decided to name this with covalent naming rules. When I challenged my teacher that I have the right answer, she responded that iron (III) trichloride is never used due to redundancy by adding the tri- prefix.

That is a very good argument on her part, but she also said that, if I can return with a good argument, she will give me the mark.

So, if anyone can tell me how to counter the argument of naming redundancy or any special properties of iron (through oxidization etc.) that I can apply into giving more reasoning for naming FeCl₃ as iron (III) trichloride.

Any information will be helpful, please do not hesitate to reply!

[Twigg]

Remember iron is a transition metal and has a bunch of d orbitals to use in coordination bonding. Does the oxidation number restrict the coordination number (number of bonds with the central iron atom)?

Also, I'm not sure on this, but I remember the electronegativity of Cl as being 3.5. might want to check that. Even so, there's room for argument.

[Serring101]

Nice Twigg, coordination bonding sounds good. (I understand coordinate covalent bonds by that)

I'll go see what I can do about that.

Thanks a lot for your help Twigg.

BTW, Chlorine's electronegativity: Electronegativity (Pauling Scale): 3.16 Source <http://www.chemicool.com/elements/chlorine.html>

Any other help is well appreciated!