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# Is this the right way of working out bond pairs and lone pairs? watch

1. (Original post by piece_by_piece)
Sn has 4 outer electrons
Cl donates 1 x 2 electrons= 2
The total number of electrons= 4+2=6
The number of electron pairs= 6/2=3
The number of bonding pairs is 2, and there is 1 lone pair.
The shape is based on trigonal planer.
Oh so does trigonal planar work for non regular shapes too? This is ridiculous, the sheet i was given is absolute crap.
2. (Original post by DaveJ)
Hmm well then I wonder why that isn't right... cos Xe only has eight in outer shell.
Yeah see thats where I thought the spdf thing came in. Ah well, i'm just gonna ignore the 26.
3. (Original post by BrightGirl)
Yeah see thats where I thought the spdf thing came in. Ah well, i'm just gonna ignore the 26.
It could be to do with the lanthanides and actinides, confusing things. But that's a guess lol.
4. (Original post by BrightGirl)
Oh so does trigonal planar work for non regular shapes too? This is ridiculous, the sheet i was given is absolute crap.
It's based on trigonal planer because there are 3 electron pairs, but I think its actual shape is bent linear. I'm not 100% certain though I think the angle would be 117.5 degrees (120-2.5) because the lone pair lone pair repulsions are greater than the bonding pair bonding pair repulsion and this "presses down" on the molecule, causing its bond angle to change.
5. (Original post by BrightGirl)
Wait hang on a minute.

For SnCl2, Sn has 4 in its outer shell, and Cl has 7. So there's 1 lone pair and 2 bond pairs, which can't be right cos in my table, we've only done 3 scenarios (3 bond pairs + 1 lone, 2 bond pairs + 2 lone, 4 bond pairs + 2 lone)
Tin (II) chloride is ionic, not covalent so the issue of shape doesn't arise.
6. SnCl2 would be bent in the gas phase, and is a chloride-bridged solid.
7. Wait surely if there are 2 bonding pairs and 1 lone pair, it isn't trigonal planar, but is instead a bent molecule with bond angle of 110 degrees?
8. (Original post by DaveJ)
Wait surely if there are 2 bonding pairs and 1 lone pair, it isn't trigonal planar, but is instead a bent molecule with bond angle of 110 degrees?
Yeah, but its a bent trigonal planar shape with respect to the electron density. As for the exact angles VESPR isn't great for that

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