Draw Lewis structures for each molecular formula. C2H4Cl2 (two isomers) C3H8O (three isomers)
The Correct Answer and Explanation is:
C₂H₄Cl₂ (1,2-Dichloroethane and 1,1-Dichloroethane)
1. 1,2-Dichloroethane
H H
| |
Cl–C–C–Cl
| |
H H
- Each carbon forms 4 bonds: 2 H, 1 Cl, and 1 C.
- Chlorines are on different carbon atoms.
2. 1,1-Dichloroethane
H
|
Cl–C–C–H
| |
Cl H
|
H
- Both Cl atoms are attached to the same carbon.
- Still satisfies carbon’s tetravalency.
C₃H₈O (Alcohol and Ether Isomers)
1. Propan-1-ol
H H H
| | |
H–C–C–C–OH
| |
H H
- Hydroxyl (-OH) group is on end carbon.
- A straight-chain primary alcohol.
2. Propan-2-ol
OH
|
H–C–C–C–H
| | |
H H H
- Hydroxyl group is on the middle carbon.
- A secondary alcohol.
3. Methoxyethane (Ethyl methyl ether)
H H H
| | |
H–C–O–C–C–H
| |
H H
- An ether, with the oxygen bonded between two carbon chains.
Explanation
Lewis structures are diagrams that show how atoms are bonded in a molecule and where lone pairs of electrons reside. They obey the octet rule, where atoms (especially C, N, O, and halogens) try to have eight electrons in their valence shell.
C₂H₄Cl₂:
This molecule has two isomers because the two chlorine atoms can either be on the same carbon or on separate carbon atoms. The 1,1-dichloroethane has both Cl atoms on the same carbon (a geminal isomer), while 1,2-dichloroethane has Cl atoms on adjacent carbon atoms (a vicinal isomer). Each carbon atom forms 4 bonds (tetravalent), and hydrogen and chlorine each form 1 bond. These molecules are constitutional isomers, differing in the connectivity of atoms.
C₃H₈O:
This molecular formula represents three isomers: two alcohols and one ether. In propan-1-ol and propan-2-ol, the OH group is connected to different carbon atoms in the propane chain. These are positional isomers of each other. In methoxyethane, the oxygen is bonded to two different carbon chains, forming an ether. Unlike alcohols, ethers have no OH group, and this structural difference leads to different chemical properties (e.g., boiling points, solubility).
Understanding these isomers is important in organic chemistry because structure heavily influences physical and chemical properties, including reactivity and intermolecular forces. Drawing Lewis structures ensures a correct visualization of electron distribution, essential for predicting behavior in reactions.
