[Ter]

Hi I don't quite understand these two questions, please help me out, I'd really really appreciate it!

For the SnCl molecule, the lewis dot diagram is
Cl
. .
: Sn
. .
Cl

But Sn does not have 8 electrons! Is it another electron deficient species? I only know of Boron and Berrylium to be electron deficient, why is this the correct Lewis structure when Sn does not have a full octet? Moreover, it's >period 3, it should have an expanded octet.. no?


2.) I don't get why van Der waals forces in CH3CH2CH2SH is stronger than in CH3CH2CH2CH3, both have 26 electrons don't they?



Thank you so very much, 
J.