Question

What decides the color of a compound ? Explain briefly.

Answer 1

Hint: Chemical colour is a physical characteristic that results from the excitation of electrons caused by the chemical's energy absorption. The complementary colour resulting from the elimination of the absorbed wavelengths is what is perceived by the eye, not the colour absorbed. Atomic spectroscopy was the first to notice this spectral viewpoint. Spectroscopy is a term used to describe the study of chemical structure using energy absorption and release.

Complete answer:
All atoms and molecules may absorb and release energy in the form of photons, which is followed by a quantum state shift. The difference between the energies of the two quantum states is the amount of energy received or released. There are many other kinds of quantum states, such as the rotational and vibrational states of a molecule. However, visible light, or energy released visible to the human eye, has wavelengths ranging from 380 nm to 760 nm, depending on the person, and photons in this range are generally associated with a change in atomic or molecular orbital quantum state.
Three types of colour receptors in the eye control light perception, each of which is sensitive to distinct wavelength ranges within this band. The Planck-Einstein relation,
$E=hf=\dfrac{hc}{\lambda }$
where E is the energy of the quantum (photon), f is the frequency of the light wave, h is Planck's constant, w is the wavelength, and c is the speed of light, determines the connection between energy and wavelength.
When photons of a specific wavelength are absorbed by matter, we perceive the complementary hue, which is made up of the remaining visible wavelengths, when light is reflected from or transmitted through that matter.

Wavelength (nm)	Color	Complementary color
400–424	Violet	Yellow
424–491	Blue	Orange
491–570	Green	Red
570–585	Yellow	Violet
585–647	Orange	Blue
647–700	Red	Green

This is merely a rough guide; for example, if a small range of wavelengths within the band 647-700 is absorbed, the blue and green receptors will be fully excited, resulting in cyan, while the red receptor would be partially stimulated, resulting in a greyish colour.

Note:
The colour of light is determined by the amount of valence electrons present in a compound's outermost orbit. These electrons absorb a certain wavelength of visible light and emit a colour that is complementary to the wavelength absorbed.
When a compound absorbs violet colour, it takes on a green-yellow hue (complementary to violet).