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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: ch3mfreak018 on August 24, 2006, 05:25:13 AM

Title: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: ch3mfreak018 on August 24, 2006, 05:25:13 AM

I would like to ask....Why is the melting and boiling points of SiCl4 lower than that of CCl4? i would think that the van der waals forces is stronger in SiCl4....Anyone can help?

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: senseless on August 26, 2006, 05:30:32 AM

Hello,

May i ask why the melting point of CCl4 higher than that of SiCl4?

Thanks!

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: Borek on August 26, 2006, 06:06:25 AM

Please search forums before posting your questions - same question was asked two days ago:

http://www.chemicalforums.com/index.php?topic=10175.0

Not that it was answered. Just asked.

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: Winga on August 26, 2006, 02:14:11 PM

M.P.
CCl4 has a better packing efficiency as it is smaller.

B.P.
I think the contact area between CCl4 molecules is larger.

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: senseless on August 27, 2006, 04:05:02 AM

 :) I dont quite get the part about CCl4 having more contact area thus resulting in its higher b.p. Can You explain further? Thanks! :)

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: Donaldson Tan on August 27, 2006, 06:44:05 AM

CCl4 is smaller than SiCl4, so it has greater contact area.

It is like comparing which has a greater contact area - Iron powder or a block of Iron

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: Winga on August 27, 2006, 08:07:12 AM

Quote from: geodome on August 27, 2006, 06:44:05 AM

CCl4 is smaller than SiCl4, so it has greater contact area.

It is like comparing which has a greater contact area - Iron powder or a block of Iron

But I wonder GeCl4 has the highest boiling point of the three.

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: senseless on August 27, 2006, 09:43:13 AM

Hmm..AlCl3 has a higher m.p and b.p compared to BCl3. Why is it that the same reasons,for CCl4 having a higher m.p. and b.p., cant be applied to AlCl3 and BCl3?

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: Winga on August 28, 2006, 11:20:59 AM

Quote from: senseless on August 27, 2006, 09:43:13 AM

Hmm..AlCl3 has a higher m.p and b.p compared to BCl3. Why is it that the same reasons,for CCl4 having a higher m.p. and b.p., cant be applied to AlCl3 and BCl3?

Do you know how do the AlCl3 molecules interact(bonding) in solid/liquid state?
Same question for BCl3...

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: senseless on August 29, 2006, 11:48:36 AM

sorry i forgot that they dimerise. hmm so are there any examples which will require this explanations or is this a stand-alone case? Thanks! ;)

Title: Re: Boiling/melting points of silcon(IV) chloride and carbon tetrachloride
Post by: Winga on August 29, 2006, 12:55:05 PM

There maybe several factors govern the m.p./b.p. of the substances.
What you need to do is that to find out which is the dominant factor, so, you don't need to worry about which are similar cases or which are not.

A better term for the explanation is total contact surface area, just like geodome mentioned.