[ajamil92]

Hello,

The aluminum chlorides in question are : AlCl3 and Al2Cl6.

Firstly, On of the previous exams in my examination board had the question whether MgCl2 or AlCl3 is ionic with covalent character. they said it was MgCl2, however after looking in a book by Nelson Thornes, it clearly states that AlCl3 is as well ionic with some covalent character. so which one is it, and what is the reason behind it?

Secondly, is Al2Cl3 more covalent than ionic? you know, since it forms dative covalent bonds ...

Thank you,

[Borek]

As far as I remember AlCl₃ is much more covalent then ionic.

[Rhubarb]

Can anyone explain why?  I used to think a metal + a non-metal produced a ionic bond and 2 non-metals produced a covalent bond
(don't take this at face value though I really might be wrong)

[danago]

Can anyone explain why?  I used to think a metal + a non-metal produced a ionic bond and 2 non-metals produced a covalent bond
(don't take this at face value though I really might be wrong)

From what i understand, "covalent" and "ionic" are just two extremes which may characterize a substances properties, but in reality, most substances lie somewhere in between, showing covalent or ionic properties to differing extents. A substance can be "more covalent" or "more ionic" than another, depending on the nature of the elements involved. I believe it is largely related to the relative sizes of the ions involved and the charge densities, but this is probably better answered by someone who knows more.

[ajamil92]

Well, here is the thing. it all about where the electrons go, generally non-metals are electronegative (meaning that they have power to pull away electrons from another element), ionic bonding occurs when bonding non-metals and metals because metals are least electronegative(in the first group of metals it is much easier to have nobel gas electronic configuration by losing 1 electron rather than gaining another 7, therfore least electronegative group) while nonmetals are most electronegative, meaning that they will not share the bonded electrons but instead the non-metals will take it all together, hence forming an ionic bond.

Now aluminium is a tricky one, Aluminium, a metal is in group 3 and at the borderline between metals and non-metals. therefore it is more electrongetive than other metal groups in the same period. so it is less easy for an electronegative non-metal to take all its valence electrons, therefore there is a probability they might be shared. HOWEVER, i believe it depends on the non-metal you are combining it with, Nitogen, Oxygen, Flourine and somewhat Chlorine are the most electronegative elements, therefore would have the greatest potential to pull electrons towards them, thus form ionic bonds with metals. in this case i am asking about aluminium chloride (AlCl3), i believe it should be an ionic compound with some covalent character,in other words electrons are pulled towards chlorine but not as close as with other less electronegative metals. i also think that if alumnium is combined to less electronegative elements such as iodine it would definetly form covalent bonds.

But what about Al2Cl6 i was asking about too... we know that when AlCl3 is formed , there are 2 lone pairs of electrons used, thus is AlCl3 is heated to about 180oC becomes a gas and forms a dimer , where 2 chlorines form a dative covalent bond with aluminium, hence i believe Al2Cl6 is a covalent compound.

My problem is that i have  very reliable sources telling me differnet facts...

I hope someone will help me with a suitable explanation and thank you,

[aldoxime_amine]

ajamil92, what you have written is only a general observation, it is not always true. You may like to see http://en.wikipedia.org/wiki/Fajans'_rules

[ajamil92]

Yes, i am aware of the other conditions, but i am not going to write a full explanation on this post... but my question still lies, whether Al2Cl6 and AlCl3 is more ionic or more covalent?