When an object absorbs certain wavelengths of electromagnetic radiation (light) while transmitting or reflecting others, it is due to the interaction between the incident light and the object's atomic or molecular structure. The absorption behavior of an object is determined by a few key factors:
Energy Levels: At the atomic or molecular level, the electrons in the object's constituent atoms or molecules occupy specific energy levels. These energy levels are quantized, meaning they can only exist at certain discrete values. When electromagnetic radiation interacts with the object, it can promote electrons from lower energy levels to higher energy levels through a process known as electronic excitation. The energy required for this excitation corresponds to specific wavelengths of light.
Energy Differences: The energy difference between different electron energy levels in the object corresponds to specific wavelengths of light that can be absorbed. According to the quantized nature of energy levels, only light with energies matching these differences will be absorbed by the object. Other wavelengths that do not match the energy differences will be transmitted or reflected.
Absorption Spectra: Each object has its own unique absorption spectrum, which represents the wavelengths of light that it selectively absorbs. The absorption spectrum is determined by the specific atomic or molecular structure of the object. Different atoms or molecules have different energy level configurations, resulting in different absorption behaviors.
Molecular Bonds: The nature of the chemical bonds within the object's atoms or molecules can also influence its absorption properties. Different types of bonds, such as covalent, ionic, or metallic bonds, have different electronic structures and energy level configurations. This can lead to variations in absorption spectra.
The combined effect of the above factors determines which wavelengths of light are absorbed by an object. When light of a specific wavelength matches the energy difference between electron energy levels in the object, it is absorbed, transferring energy to the object's atoms or molecules. The absorbed energy may be converted into heat or result in other forms of molecular or atomic excitation. The remaining wavelengths that do not match the energy differences are either transmitted through the object or reflected back, giving rise to the object's observed color or appearance.