Confusion with molecular geometry [carbon tetrachloride]

1. Jul 28, 2011

sinjan.j

Confusion with molecular geometry [carbon tetrachloride]

I'm trying to understand the molecular geometry of four different compounds:

$CCl_{4} ,CHCl_{3} ,CH_{2}Cl_{2} ,CH_{3}Cl$

Please tell me whether my thinking is right or not[conceptually]. If it's wrong kindly correct me.

for $CCl_{4}$

Carbon forms 4 different single bonds with chlorine. While deciding the shape of the molecule, we have to take into consideration the lone pairs and bond pairs of carbon. Since, lone pairs of carbon don't exist, we have to make sure that the angle between the bond pairs of electron of carbon is maximum and that is possible through tetrahedral arrangement. So, the shape is tetrahedral.

for $CHCl_{3} , CH_{2}Cl_{2} , CH_{3}Cl$

Same as the above arguement, therefore tetrahedral.

Am I right?

I have another doubt. While deciding the geomerty of the molecules, why do we have to consider the electrons of the valence shell of the central atom only, and why not the electrons of the valence shell of the peripheral atoms?

2. Jul 28, 2011

Yanick

Yes you are correct.

You don't have to, it just doesn't make sense to talk about the geometry about the chlorine in carbon tetrachloride. Water adopts a bent geometry because of the lone pairs on the Oxygen, we don't really talk about the geometry around the Hydrogens.

When thinking about molecular geometry, you are trying to systematically model what a molecule may look like in space, hence we say that water adopts a bent geometry instead of saying that the geometry around the Hydrogen (in water) is X.

Hope that helps.

3. Jul 28, 2011

sinjan.j

Thank You. got it.