Dichloroethylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2}\right)\) has three forms (isomers), each of which is a different substance. (a) Draw Lewis structures of the three isomers, all of which have a carbon-carbon double bond. \((\mathbf{b})\) Which of these isomers has a zero dipole moment? (c) How many isomeric forms can chloroethylene, $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}$, have? Would thev be expected to have dipole moments?

To draw the Lewis structures for dichloroethylene, we need to understand that it is composed of 2 carbon, 2 hydrogen, and 2 chlorine atoms. The isomers are molecules with the same molecular formula but with different structures or spatial arrangements of atoms.

Since all isomers have a carbon-carbon double bond, the three possible isomers for dichloroethylene can be drawn by placing chlorine atoms on different carbons in the molecule: 1. 1,1-dichloroethylene: Both chlorine atoms are attached to the first carbon atom. Cl | H - C = C - H 2. cis-1,2-dichloroethylene: The chlorine atoms are on different carbon atoms, on the same side. Cl Cl | | H - C = C - H 3. trans-1,2-dichloroethylene: The chlorine atoms are on different carbon atoms, but opposite sides. Cl H | | H - C = C - Cl

In order to find which isomer has a zero dipole moment, we need to look at the molecular geometry and electronegativity differences between atoms. 1. In 1,1-dichloroethylene, the two chlorine atoms have equal electronegativity and are attached to the same carbon atom. This results in an overall non-zero dipole moment, as there is an unsymmetrical distribution of charges. 2. In cis-1,2-dichloroethylene, the two chlorine atoms are on the same side of the molecule and have similar electronegativity. Hence, there is an overall non-zero dipole moment due to the unsymmetrical distribution of charges. 3. In trans-1,2-dichloroethylene, the two chlorine atoms are on opposite sides of the molecule, making the molecule symmetric in terms of charge distribution. This results in a zero dipole moment. So, trans-1,2-dichloroethylene is the isomer with a zero dipole moment.

In chloroethylene (\(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\)), there are 2 carbon, 3 hydrogen, and 1 chlorine atoms. Since we still have a carbon-carbon double bond, the only possible isomers would include one with the chlorine atom on the first carbon atom and one with the chlorine atom on the second carbon atom: 1. 1-chloroethylene: Chlorine is attached to the first (primary) carbon atom. Cl | H - C = C - H - H 2. 2-chloroethylene: Chlorine is attached to the second (secondary) carbon atom. H Cl | | H - C = C - H - H Chloroethylene has 2 isomeric forms.

Both 1-chloroethylene and 2-chloroethylene have unsymmetrical charge distributions due to the electronegativity difference between carbon, hydrogen, and chlorine atoms. As a result, both isomeric forms of chloroethylene would be expected to have dipole moments.