Practise counting bonding and lone pairs, predicting geometry and explaining bond-angle compression when lone-pair repulsion exceeds bond-pair repulsion using Edexcel IAL Chemistry evidence.
The elements carbon and silicon both form dioxides.
The shape of the carbon dioxide molecule affects its physical properties.
Explain the shape of the carbon dioxide molecule.
An explanation that makes reference to the following points:
- there are two sets of bonding electrons (and no lone pairs) about the carbon atom
- which arrange to minimise repulsion (1)
- resulting in a linear shape / bond angle of 180^ (1)
Any indication of two regions of electrons (this includes a correct diagram) e.g. O=C=O
Allow two double bonds
Allow maximum separation / to be as far apart as possible
Accept bond angle labelled on a diagram
Ignore references to symmetry Ignore references to lone pairs on oxygen
All marks are independent
No TE for any mark