The CO2 molecule is linear with the carbon atom in the centre between two oxygen atoms which are both double bonded to it.


Although the bonds are quite highly polarised as they are colinear there is no permanent dipole on the molecule. There is however a vibration mode of the molecule that bends it out of line and generates a temporary dipole moment.

In liquid form carbon dioxide is used in fire extinguishers for electrical and similar fires as it does not conduct electricity. However it is not a good idea to use it on computer equipment as it can scramble magnetic information (due to the temporary dipole) - that's why they used to use Halon in computing centres.

Solid carbon dioxide is more commonly referred to as dry ice. It is a white powdery solid.

Carbon dioxide is toxic in relatively high concentrations. This is because haemoglobin works by complexing with oxygen or carbon dioxide to carry them round the body (oxygen in/carbon dioxide out). This is a very finely balanced equilibrium and if the external carbon dioxide concentration rises too high then it prevents the red blood cells from picking up oxygen in the lungs. This is the reason that the Apollo 13 astronauts had to get their carbon dioxide scrubbers working again (despite not being low on oxygen).

Carbon Monoxide on the other hand forms so stable a complex with haemoglobin that neither oxygen nor carbon dioxide can displace it at atmospheric pressures.

Thanks to Tiefling and Rollo who told me that this explanation was not originally clear enough.