No, not all molecules absorb electromagnetic radiation. Whether a molecule can absorb electromagnetic radiation depends on its electronic structure and the energy levels of its electrons.
Molecules can absorb electromagnetic radiation in the form of photons when the energy of the photons matches the energy difference between two electronic energy levels within the molecule. This phenomenon is known as electronic transitions. The specific wavelengths of radiation that a molecule can absorb are determined by the energy differences between these levels.
However, not all molecules have electronic energy level transitions that correspond to the energy of visible light or other parts of the electromagnetic spectrum. For example, simple diatomic molecules like oxygen (O₂) or nitrogen (N₂) do not have electronic transitions in the visible range, so they do not absorb visible light. They primarily interact with radiation in the ultraviolet (UV) range.
On the other hand, molecules with more complex structures or containing certain functional groups can absorb light in the visible or infrared regions of the electromagnetic spectrum. These molecules are often responsible for the colors we observe in dyes, pigments, and other colored substances.
In summary, whether a molecule absorbs electromagnetic radiation depends on its electronic structure and the energy differences between its electronic energy levels. Not all molecules have electronic transitions that allow them to absorb radiation across the entire electromagnetic spectrum.