What happens in a molecular level that allows an analyze to absorb light at a certain wavelength.

Question

1: What happens in a molecular level that allows an analyze to absorb light at a certain wavelength.

2: Why are you using a specific wavelength of light to record absorbance measurements for the dye (i.e., why non't every wavelength of light be absorbed by the analyte)

Answer 1

Hi Jose,

1: In an atom or molecule, electrons exist in discrete energy levels. When light is absorbed, the energy is absorbed by the atom and the electron is excited to a higher energy level. For an electron to be excited the energy of the incident light has to be the same as the energy difference between the energy levels for the electron. This is why you need a specific wavelength of light to be absorbed.

2: Many molecules absorb multiple wavelengths of light, so it depends a bit on what you are doing. If you are performing a common laboratory experiment such as using Beer's Law to determine the concentration of an unknown then it makes sense to use a single wavelength if it is absorbed efficiently. There are probably other wavelengths which are absorbed by the molecule you are investigating, but depending on a lot of information behind the scenes they may not absorb as efficiently, so it may be harder to detect.