How do you figure out if water and carbon dioxide are polar?

Electronegativity.





No electronegativity difference between two atoms leads to a pure non-polar covalent bond.





A small electronegativity difference leads to a polar covalent bond.





A large electronegativity difference leads to an ionic bond.





H2O


3.44 - 2.20 = 1.24


Pure Covalent Bond





CO2


3.44 - 2.55 = 0.89


Covalent Bond