How do Covalent Bonds Produce Color?

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SUMMARY

Covalent bonds produce color through charge transfer transitions, particularly in compounds like iron oxide and iron sulfide. In iron II sulfate, the weak green color arises from transitions within the d-orbitals of iron, indicating that covalent bonding is not the primary factor. The color variations in these compounds are attributed to ionic bonding, where negatively charged ligands transfer charge to the metal, necessitating energy that corresponds to visible light. This process is influenced by the transition dipole moment, which plays a critical role in the observed colors.

PREREQUISITES
  • Understanding of Band Theory in metallic bonds
  • Knowledge of d-orbital transitions in transition metals
  • Familiarity with ionic and covalent bonding concepts
  • Basic principles of charge transfer transitions
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  • Research the Band Theory of metallic bonds in detail
  • Explore the role of d-orbitals in transition metal chemistry
  • Study charge transfer transitions in various metal-ligand complexes
  • Investigate the color properties of other transition metal compounds
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Chemistry students, educators, and professionals interested in the optical properties of materials, particularly those studying transition metals and their compounds.

Johnleprekan
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I've learned about the Band Theory of metallic bonds and how they produce color, but how does a covalent bond produce color? Normally a metal such as iron absorbs and emits back the full range of colors due to metallic bonds, but when oxygen or sulfur get added it produces a different color. Can someone explain what happens here? One explanation for iron oxide and another for iron sulfate or iron sulfide, please. If possible explain in Layman's terms.
 
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The weak green colour of iron II sulfate is due to transitions within the d-orbitals on iron, ie, covalent bonding is not involved. The colour of the other substances is mainly due to so called charge transfer transitions. The bonding in these compounds is mainly ionic and a transfer of charge from the negatively charged ligand (e.g. sulfide in iron sulfide or oxide in iron oxide) to the metal requires both an energy corresponding to visible light and goes in line with a high transition dipole moment.
 
Thank you.
 

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