Notes:

• the stretching motion occurs in the plane defined by the C atom and the two Cl atoms
• a small amount of motion is associated with the two H atoms
• the greater displacement of the C atom compared with the Cl atoms (i.e., the Cl atoms are
  much more massive than the C atom)
• the stretching of the two C-Cl bonds is symmetric (i.e., the displacements of the C and Cl
  atoms are equal for both C-Cl bonds)
• symmetric stretching is a type of stretching motion