[polyphonics]

Hi,

I'm doing some past exam questions for my chemistry class and have a question on this one:

"Experimental data provide the basis for interpreting differences in properties of substances:
Question: Account for the differences in properties given in terms of differences in structure and bonding in each of the following pairs.

*MgCl₂ and SiCl₄
     SiCl₄:: Melting point: -70C, Electrical Conductivity of Molten State 0ohm^-1
     MgCl₂:: Melting Point: 714C Electrical Conductivity of Molten State >20ohm^-1

*MgCl₂ and MgF₂
     MgF₂:: Melting Point: 1,261C Electrical Conductivity of Molten State: >20ohm^-1
     MgCl₂:: Melting Point: 714 Electrical Conductivity of Molten State: >20ohm^-1 

     
*F₂ and N₂
     F₂:: Bond Length (angstroms): 1.42
     N₂:: Bond Length (angstroms): 1.09

*F₂ and Br₂
     F₂:: Bond Length (angstroms): 1.42
     Br₂:: Bond Length (angstroms): 2.28

I asked the teacher about this one, and she wasn't very willing to help =(.  I had tried the explanation of the differences of character using the differences in electronegativity, but the question doesn't ask for that.  Thanks. 

PS-Attached is the OCR version of the question (.RTF) if that makes it easier to read--I was too lazy to make HTML tables :O)
2nd-If this is a repost, sorry =(!  I submitted it, but it never showed up on the forum in which I intended it to be placed.