Question

As you did so well up to this point, can you help me figure out which one of this sentences

is wrong?
a) Symmetric vibrations have the characteristic of moving in sync.
b) Stretching and bending represent two different vibrations.
c) A molecule will show all 6 types of vibrations, regardless of it's geometry.
d) IR analysis are based on vibrations.

Answer 1

The incorrect sentence is (c), as the number and type of vibrations of a molecule depend on its geometry, and not all vibrations may be IR active. The correct answer is c) A molecule will show all 6 types of vibrations, regardless of it's geometry.

Step-by-step explanation:

The sentence that is incorrect is (c) A molecule will show all 6 types of vibrations, regardless of its geometry. This statement is not accurate because the number and type of vibrations a molecule can exhibit are dependent on its specific geometry.

Some vibrations may be infrared inactive, for example, the stretching vibrations of symmetrical double and triple bonds, as they do not result in a change in dipole moment, leading not to absorb IR light. However, in the context of IR spectroscopy, molecules show various active vibrations including stretching and bending, which correspond to different energies and are observable in an IR spectrum.