Page 1 of 1
Posted: Wed Nov 28, 2018 10:50 pm
Why is Sn an exception to the octet rule? (In SnCl2, Sn only has 2 single bonds and a lone pair)
Posted: Wed Nov 28, 2018 10:55 pm
It really depends on what Sn is bonding with. In your case, Cl can only accept 1 lone pair. Putting a double bond onto the Sn is not good as the formal charge of Cl will become +1 and Sn will become -1. Usually, it comes down to formal charge.
Posted: Wed Nov 28, 2018 10:59 pm
Sn wants to be in the most stable state which is when formal charge is equal to 0.
With 18 total valence electrons in the structure, and with 16 valence electrons being taken up by the two Chlorines with 3 lone pairs around each and 1 single bond linking each Cl to Sn thanks to the fact that Chlorine's formal charge will be 0 when there are 6 valence electrons and 1 bond around it, 2 valence electrons must be distributed to around Sn making Sn's formal charge 0 as it will have 1 lone pair and 2 single bonds around Sn.