Chemistry: Bonding 4a. Draw the Lewis structure for CH4, (methane), NH3, (ammonia), and H20 (water). b. Calculate the bond polarity for the C-H bond, N-H bond, and O-H bond. c. Classify these molecules as either polar or nonpolar. If the molecule is polar, label the partial negative and partial positive sides of the molecules you drew above.
Chemistry: Bonding
4a. Draw the Lewis structure for CH4, (methane), NH3, (ammonia), and H20 (water).
b. Calculate the bond polarity for the C-H bond, N-H bond, and O-H bond.
c. Classify these molecules as either polar or nonpolar. If the molecule is polar, label the partial negative and partial positive sides of the molecules you drew above.
The Correct Answer and Explanation is :
4a. Lewis Structures
- Methane (CH₄):
- Carbon (C) has 4 valence electrons, and each hydrogen (H) has 1 valence electron.
- Carbon shares its 4 valence electrons with 4 hydrogen atoms, forming 4 single bonds.
- The Lewis structure for CH₄ is:
H | H - C - H | H
- Ammonia (NH₃):
- Nitrogen (N) has 5 valence electrons, and each hydrogen (H) has 1 valence electron.
- Nitrogen shares its 3 valence electrons with 3 hydrogen atoms, forming 3 single bonds.
- The Lewis structure for NH₃ is:
H | H - N - H
- Water (H₂O):
- Oxygen (O) has 6 valence electrons, and each hydrogen (H) has 1 valence electron.
- Oxygen shares 2 of its valence electrons with 2 hydrogen atoms, forming 2 single bonds.
- The Lewis structure for H₂O is:
H - O - H
4b. Bond Polarity
- C-H bond in CH₄:
- Carbon has an electronegativity of 2.55, and hydrogen has an electronegativity of 2.20.
- The difference in electronegativity is 0.35, which is small. This means the C-H bond is nonpolar.
- N-H bond in NH₃:
- Nitrogen has an electronegativity of 3.04, and hydrogen has an electronegativity of 2.20.
- The difference in electronegativity is 0.84, which indicates a polar covalent bond. The nitrogen atom pulls the electron density slightly toward itself, creating a partial negative charge (δ-) on nitrogen and a partial positive charge (δ+) on hydrogen.
- O-H bond in H₂O:
- Oxygen has an electronegativity of 3.44, and hydrogen has an electronegativity of 2.20.
- The difference in electronegativity is 1.24, which makes the O-H bond polar. Oxygen becomes partially negative (δ-), and hydrogen becomes partially positive (δ+).
4c. Molecular Polarity
- Methane (CH₄):
- CH₄ is nonpolar because the C-H bonds are weakly polar and the symmetrical tetrahedral shape causes any dipoles to cancel out.
- Ammonia (NH₃):
- NH₃ is polar because the N-H bonds are polar, and the trigonal pyramidal shape means the dipoles do not cancel, creating a net dipole moment pointing toward nitrogen.
- Water (H₂O):
- H₂O is polar because the O-H bonds are polar, and the bent shape of the molecule results in an overall dipole with the partial negative charge on the oxygen and partial positive charges on the hydrogens.
Conclusion
- CH₄ is nonpolar.
- NH₃ and H₂O are polar molecules. In NH₃, nitrogen carries a partial negative charge, and in H₂O, oxygen carries a partial negative charge. The hydrogen atoms in both are partially positive.