Why is lead iodide yellow and lead chloride white?

• The color of a compound is determined by the interaction of light with the chemical structure and arrangement of its atoms and molecules. In the case of lead chloride (PbCl2) and lead iodide (PbI2) , the difference in color can be attributed to their respective electronic structures and the energy levels of their valence electrons.
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• Lead chloride appears white because it is a relatively transparent compound. The white color is a result of the scattering of light by the crystal lattice of PbCl2. When light passes through the crystal, it interacts with the chloride ions (Cl-) and lead ions (Pb2+), causing the light to scatter in different directions. This scattering of light across the entire visible spectrum results in the perception of white color.
  
  On the other hand, lead iodide appears yellow due to a phenomenon called the band gap. The electronic structure of lead iodide creates a larger band gap compared to lead chloride. A band gap refers to the energy difference between the valence band (where electrons are tightly bound to atoms) and the conduction band (where electrons are free to move).
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• In the case of lead iodide, the band gap is such that it absorbs and reflects light in the blue region of the visible spectrum, while allowing yellow light to be transmitted or reflected. Therefore, our eyes perceive lead iodide as yellow. It's important to note that slight variations in the composition, crystal structure, or impurities within a compound can also influence its color.