CO2 vs. H2O

[Elizabeth Ignacio 1C]

Hi! What exactly makes carbon dioxide non-polar while H2O is polar? I know that it has to do with its dipole moments, but I'm unsure how you can look at the dipole moments and determine polarity. Thanks!

[Angel Ni 2K]

1. Draw VSEPR structures.
2. Draw dipole moments.
3. CO2 has dipole moments, but they cancel out because they are equal in magnitude and opposite in direction. Therefore, CO2 is a nonpolar molecule despite having polar bonds. H2O has dipole moments, but they do not cancel out because they are equal but not opposite in direction. Therefore, H2O is a polar molecule and has polar bonds.

[Ramya Natarajan 1D]

Keep in mind that in CO2, Oxygen is more electronegative, so the dipole moments are facing opposite directions (away from the central atom of Carbon), making the molecule polar. In H2O, Oxygen is more electronegative, so the dipole moments would face inwards towards oxygen and consequently cancel out. Another thing to keep in mind is thinking of dipole moments as vectors--equal but opposite directions would cancel each other out.

[Alexandria Weinberger]

In CO2 the dipole moments cancel out, while in H2O, they don't, making it polar.

[Pooja Nair 1C]

In CO2, both oxygens are more electronegative than the carbon, but they pull equally apart from one another, so there is no dipole moment (the pulls cancel). Meanwhile, in H2O, oxygen has two lone pairs as well as the bonds to the hydrogen, so the electrons are concentrated on oxygen and are not canceled out by anything, therefore it has a dipole moment and is polar.

[mayasinha1B]

h20 is not linear, and it's dipole moments do not cancel. If you draw dipole moments on co2 then you see that they cancel out, making co2 nonpolar.

[Adrian Lim 1G]

H20 has a bent structure, so the dipole moments that move towards the more electronegative oxygen do not cancel out, making H20 polar. However, in CO2, the structure is linear, meaning the dipole moments would end up cancelling out each other, making it non polar.