[akrnfl]

SnCl2 is solid but SnCl4 is liquid, why?

[FeLiXe]

maybe because Sn⁴⁺ wouldn't be stable in an ionic crystal

[Alberto_Kravina]

Very interesting topic, I didn't think that salt that appears pretty "normal" in its composition (e.g. a transition metal and a Grp. 7 Element) can be liquid at room temperature.
I also think that the most plausible answer is that maybe Sn⁴⁺ is not stable in a ionic Crystal, I think because  its ionic radius is "incompatible" with 4 chloride ions and so the attraction forces inside the crystal are weaker.

http://en.wikipedia.org/wiki/SnCl4

[FeLiXe]

I think most high metal chlorides are either liquid or volatile

TiCl4 is liquid

AlCl3 is volatile

FeCl3 is fairly volatile

It does not seem like Chlorine is willing to make stable ionic compounds with highly charged metals.

I would say it is because of the covalent character of the bond. You don't get a whole electron from a particle that's 4+

[woelen]

The higher the oxidation state of a metal, the more covalent its compounds are.

E.g. CrO is purely saline/ionic, and it is purely basic.
Cr2O3 is not really covalent, but also not purely ionic. It is both. It also reacts amphoteric and can be basic, but also acidic.
CrO3 is purely covalent, it has a low melting point, and it is purely acidic.

This trend is true for any element. So, SnCl2 is mostly ionic, SnCl4 is covalent. The latter is not a salt.

Yet another example: VCl2 is a salt, VCl3 we also still consider a salt, but it is not purely ionic. VCl4 is not a salt anymore, it is a brown liquid.

Metal compounds do not need to be salts. I have made some CrO2Cl2, which is a purely covalent compound of chromium, and which has a nice red vapor at room temperature. So, we can even have gaseous metal compounds.

[AWK]

Many oxides and halogenides in highest oxidation states are covalent compounds, eg: Mn2O7, OsO4, SnCl4,  and so on

[mdlhvn]

I think the problem seem to be expand
The initial question is why SnCl2 is liquid and SnCl4 is solid. I appreciate all the answers. However, it seems that some ionic compounds is solid and covalent compounds is liquid.

Mn2O7, CrO3, OsO4, are all covalent (you said) and solid

SnCl4 is covalent and liqid?

[FeLiXe]

ionic substances always make crystals

for covalent bonds it depends on the elements valency

covalent chloride can only bond to one atom, therefore you have separate molecules -> liquid

covalent oxygen compounds are polymeric crystals. every oxygen bonds with two different atoms and the whole thing stays together

[mdlhvn]

Nice explanation. Thanks

[AWK]

I think the problem seem to be expand
The initial question is why SnCl2 is liquid and SnCl4 is solid. I appreciate all the answers. However, it seems that some ionic compounds is solid and covalent compounds is liquid.

Mn2O7, CrO3, OsO4, are all covalent (you said) and solid

SnCl4 is covalent and liqid?

I said Mn2O7, CrO3, OsO4, are all covalent. They are liqids, eq boiling point of OsO4 is about 120 C