There are three Lewis structures for C2H2Cl2. Please draw the following three structures. 2. Explain why one of the three structures for C2H2Cl2 is nonpolar, and the other two have molecular dipoles. 3. There are three Lewis structures for [NO3]-. Compare the molecular polarity of the three structures.
The Correct Answer and Explanation is:
. Three Lewis Structures for C2H2Cl2:
There are two possible positions for chlorine (Cl) atoms in C2H2Cl2 (dichloroethene) that lead to three distinct isomers:
- cis-C2H2Cl2 (Z-isomer):
- Cl atoms are on the same side of the double bond.
- H atoms are on the opposite side.
- trans-C2H2Cl2 (E-isomer):
- Cl atoms are on opposite sides of the double bond.
- H atoms are on opposite sides as well.
- 1,1-Dichloroethene:
- Both Cl atoms are attached to the same carbon atom, while the other carbon is bonded to two hydrogen atoms.
2. Polarity of the Three Structures:
- cis-C2H2Cl2 (Z-isomer):
- This structure is polar because the dipoles of the C-Cl bonds do not cancel each other. The chlorine atoms are on the same side, creating an uneven distribution of charge that results in a net dipole moment.
- trans-C2H2Cl2 (E-isomer):
- This structure is polar as well because while the C-Cl bond dipoles are in opposite directions, the electronegativity difference between C and Cl creates a molecular dipole. The symmetry of the molecule doesn’t result in perfect cancellation, and so it remains polar.
- 1,1-Dichloroethene:
- This molecule is nonpolar due to the symmetry of the structure. The chlorine atoms are attached to the same carbon, and the dipoles cancel each other out, resulting in no net dipole moment.
3. Molecular Polarity of [NO3]-:
The nitrate ion (NO3-) can have resonance structures:
- Resonance Structure 1:
- One nitrogen-oxygen double bond, two nitrogen-oxygen single bonds with one lone pair on each oxygen.
- The molecule has symmetry, and the dipoles cancel out.
- Resonance Structure 2:
- The nitrogen is bonded to one oxygen via a single bond and to two oxygens via double bonds, with a lone pair on the single-bonded oxygen.
- Like the first structure, this structure has symmetry, leading to no overall dipole moment.
- Resonance Structure 3:
- Similar to the previous structures, just with the locations of the double bonds and lone pairs shifted.
- This structure also has symmetry and no dipole moment.
All three resonance structures of NO3- are nonpolar overall because of their symmetry, which causes the individual bond dipoles to cancel out.
