SnCl2 is solid but SnCl4 is liquid, why?12AX7 - 11-11-2006 at 09:14
Low binding energy. See also TiCl4.
Timakrnfl - 11-11-2006 at 09:36
Could you please tell more12AX7 - 11-11-2006 at 10:52
Not really. It doesn't gain enough energy by sticking together...so it doesn't.
This is generally viewed as a comparison of covalent (think stick-and-ball molecule model) to ionic (positive and negative charges locked in a
crystal) bonding. Covalent bonds are localized and tend to form discrete molecules (CH4, SiCl4, etc.), whereas ionic bonds are between ions, discrete
spheres of some charge (positive and negative), stuck together on all sides by their mutual attraction to opposites, in a regular pattern due to their
size difference (and shape, for compound ions like carbonate) and mutual repulsion of like charges.
In short, charges (that is, ions) stick together in the pattern they do because it's the pattern of highest energy. Go ahead and calculate it for a
variety of crystal shapes, using coulomb's law. Whereas covalent molecules don't stick together very well because their bonds are inward holding the
molecule together, leaving little attention to the outside appearance. Polarization and dispersion forces provide the stiction that holds together
the liquids TiCl4 and SnCl4, but not enough (at room temperature) to form a solid.
No, it isn't a satisfactory answer to say "the most favorable energy state", but when you go through the adventure of discovering what's at work,
you'll eventually come right back to where you started, this time thinking "because it IS the most favorable energy state"!
Timguy - 11-11-2006 at 13:10
Because it has a lot more covalent character. Also it has no dipole moment due to the symetrical shape (think carbon tetrachloride).turd - 12-11-2006 at 11:08
CH2 (Polyethylene) is solid but CH4 is gaseous, why?
Yes, that analogy was bad, but you get the point.Blind Angel - 12-11-2006 at 11:14
CH2 is in fact (CH2)x where x is a very very big number, you end up with a gigantic molecule in fact, who are called polymers, CH4 on the contrary is
a single molecule.
Code:
H
|
CH4= H-C-H
|
H
H H H H H
| | | | |
Polymers = ...-C-C-C-C-C-...
| | | | |
H H H H H
[Edited on 12-11-2006 by Blind Angel]turd - 12-11-2006 at 11:39
Good, and now let's apply our knowledge on SnCl2 vs. SnCl4 (keyword: coordination polymer).
