AS Chemistry- helping each other out!

hi! Sorry if i've done this wrong this is my first post! I'm doing AQA AS Chem and the spec says "appreciate the usefulness of these reactions (nucleophillic substitution) in organic synthesis" but i don't really have any specific examples and was wondering if someone could help me out thank youuuu

Hi guys this may be a really stupid question but I was wondering why is CCl2 isn't the BENT shape so wouldn't the angle be 104.5 if it has one lone pair? I'm really confused not sure where 118 degrees has come from

Hi guys this may be a really stupid question but I was wondering why is CCl2 isn't the BENT shape so wouldn't the angle be 104.5 if it has one lone pair? I'm really confused not sure where 118 degrees has come from

Posted from TSR Mobile

CCL2 has 2 bonding pairs and a lone pair,so it's non linear with a bond angle of 104.5 degrees.

If you draw the dot and cross diagram for CCl2 and, say, H2O, you see that because carbon only has 4 outer electrons 2 join in the bonding which leaves 2 electrons - ie 1 lone pair. In H2O you have 4 electrons left, so 2 lone pairs. This means that in CCl2 it is trigonal planar but with the lone pair pushing the bond angle out.

Hi guys this may be a really stupid question but I was wondering why is CCl2 isn't the BENT shape so wouldn't the angle be 104.5 if it has one lone pair? I'm really confused not sure where 118 degrees has come from

Bent shapes are for molecules that have two bonding pairs and two lone pairs like H₂0.


*Please note that that diagram should say 104.5^o

CCl₂ has two bonding pairs and one lone pair of electrons.
As we know for every lone pair added to a molecule the bond angle is reduced 2.5^o.
So in this case we should reduce 120^o (angle for 3 bonding pairs) by 2.5^o because a lone pair is added to the structure of CCl₂.

I hope that helps

Ohh thank you so much! this made a lot of sense

but where has the 118 come from?

Oh you're welcome, I'm glad you found that useful.

May I ask what exam board you are and how old that question is?

Oh you're welcome, I'm glad you found that useful.

May I ask what exam board you are and how old that question is?

i thought it was a bent shape?

It's AQA and the past paper was from 2002

Ah okay I'm AQA too, and I'm now doing A2.

The reason why I asked as to how old it was was because the CCl₂ shape is actually pretty different as we it has 2 bonding pairs and 1 lone pair and I don't think it is the specification to know the name of a shape for a molecule with that combination.

I thought it was best you know

I also attached a document that has all the Unit 1 topic by topic questions with the mark schemes, I used this last year to help me thought you might like it

No clue if this picture is at all legible (Cameras a bit rubbish & my handwriting is scruffy).
The writing says 'two lone pair .'. 104.5' 'These two act as one lone pair' 'so trigonal planar and 120-2 = 118'

I'm so sorry I thought that made a lot of sense but why are you reducing 120 ?

Ah right.
As you'll notice from the diagram in your question that they're trying to make students see a link between BCl₃ and CCl_2.


The link between these two is that both molecules have 3 bonds whether it be electron bonds or lone pairs.

The maximum bond angle for a molecule with 3 bonds is 120^o, so this should be used as a base for students when tackling this question.

In CCl₂ you'll see that one electron pair has been replaced by a lone pair and as we discussed earlier for every lone pair added we reduced the bond angle by 2.5^o. This makes the bond angle in CCl₂ 117.5^o.

Does that make more sense know?