Explain why H2O is polar and CO2 is nonpolar.(hint: draw the electron dot structure first)
The correct answer and explanation is :
To understand why water (H₂O) is polar and carbon dioxide (CO₂) is nonpolar, let’s first examine their molecular structures, specifically through their electron dot structures (Lewis structures), and then discuss the distribution of charge within each molecule.
H₂O (Water) – Polar Molecule:
- Electron Dot Structure of H₂O:
- Oxygen (O) has 6 valence electrons, and each hydrogen (H) atom has 1 valence electron.
- Oxygen bonds with two hydrogen atoms to form two single bonds. This gives oxygen a total of 8 electrons in its valence shell (2 from each hydrogen bond and 4 from lone pairs).
- The structure of water is bent, with a bond angle of approximately 104.5°.
- Polarity of H₂O:
- Oxygen is more electronegative than hydrogen, meaning it attracts shared electrons more strongly.
- This creates partial negative charges (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms.
- The bent shape of H₂O (due to the lone pairs on oxygen) results in an uneven distribution of charge. The dipoles (partial positive and partial negative charges) do not cancel each other out, creating a net dipole moment.
- The molecule is polar because it has a positive and negative end, leading to an overall dipole.
CO₂ (Carbon Dioxide) – Nonpolar Molecule:
- Electron Dot Structure of CO₂:
- Carbon (C) has 4 valence electrons, and oxygen (O) has 6. Each oxygen atom forms a double bond with carbon, creating two bonds with carbon and 2 lone pairs of electrons on each oxygen.
- The structure of CO₂ is linear, with a bond angle of 180°.
- Polarity of CO₂:
- Oxygen is more electronegative than carbon, so each C=O bond has a dipole with the oxygen being partially negative and the carbon being partially positive.
- However, because CO₂ is linear, the two bond dipoles are equal in magnitude and opposite in direction, effectively canceling each other out.
- As a result, CO₂ does not have a net dipole moment, making it a nonpolar molecule.
Conclusion:
- H₂O is polar due to its bent shape and the unequal sharing of electrons between oxygen and hydrogen, resulting in a net dipole moment.
- CO₂ is nonpolar because its linear geometry causes the individual bond dipoles to cancel each other out, resulting in no net dipole moment.