Why the transition elements are coloured but those s-block and p-block elements are colourless?

Answer 1

A substance appears colored because it absorbs light at specific wavelengths in the visible part of the electromagnetic spectrum and transmits or reflects the rest of wavelength. Each wavelength of visible light represents a different color.

Most of the compounds if transition metals are colored in the solid or solution state. This is due the fact that the transition metal ions in them are colored. coloration of metal ions arises from the excitation of electrons from the d-orbitals of lower energy to d-orbitals of higher energy.The energy required for d-d electron excitation is available in the visible range. it is for this reason that transition metal ions have the property to absorb certain radiations from visible region and exhibit he complementary color.

Transition metal ions having completely filled or empty d-orbitals are colorless. In both cases excitation of electrons to higher orbitals is not possible.

for further info read about atomic structure, spectrum and colors.

Answer 2

The chemical compounds of the transition metal compounds are often colred- and this is due to d electrons being excited by visible light into higher energy levels within the compound. These d electrons are not present in the s p block elemnts so these are generally colorless. There are many exceptions- particularly in organic chemistry one example are pigments such as carotene with conjugated double bonds which absorbs visible light.

The elements are another issue- the non-metallic s-p block elements are often colored, think of the halogens, sulfur as examples. again these have low level orbitals into which electrons can be excited by visible light.