Valence bond theory or resonance theory
Valence bond theory explain following things about the structure of dye.
These are the groups of atoms, the π -e- of which may get transferred from group state to excited state by absorption of radiation, thus Producing the colour. the excitation take place due to absorption of light in visible region.
These are groups which tend to increase the resonance by interacting the unshared pair of e- on N Or oxygen atoms with π – e- of aromatic rings. more the resonance more the intensity of absorption of light and also shift the absorption bond to longer wavelength. hence, there occurs the deepening of the colour.
3. Dipole moment
As the oscillation of e- pair take place, the dipole moment charges.
[ N=O > C=S > N=N > C=O > C=N > C=C ]
the colour depends in the opposite direction due to increase in no of cononical structure.
read also : – Activated sludge process
Important of valance bond theory
The main theory is formation of strong bonds. this theory is indicated development of covalent bond in molecules. It also develop overlap of atomic orbitals.