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sjatania

Why the compounds of transition elements are coloured ?

raman_1290

this is because of presence of unpaired electrons in valance sell of the transition elements.

apurvanaik

Different colours result from the same composition of light after it has been reflected transmited or absorb after hitting a substance.Transiton elements have vacant d-orbitals. The electrons take up energy from visible reasion and move to higher energy levels. hence they absord energy in the form of light and the compounds become colourd.
The colour depends upon the nature of metal ion (no. of electrons in d-orbital), the arrengment in space ect.

apurvanaik

I think the coloured compound are not due to unpaird electrons.
because of unpaired electrons transition elements are paramagnetic.

magiclko

as its bit tym taking typing all the stuff, here are some useful links

http://www.chemguide.co.uk/inorganic/complexions/colour.html

http://chemlearn.chem.indiana.edu/demos/22-2%20Colors%20of%20Transition%20Metal%20Ions.htm

http://en.wikipedia.org/wiki/Transition_metal#Colored_compounds

rameshkumar

it is due to unpaire eletron in vanlance shell,when light incident on it ,they vibrate with frequency of visible light.

devjani

A substance apears colored bcoz it absorbs light at specific wavelengths in the visible region of the electromagnetic spectrum (4000 - 7000 A') and transmits or reflects the rest of the wavelengths .

The colour of transition metal ions arises from the excitation of electrons from the d-orbitals of lower energy to the d-orbitals of higher energy.

The energy required for d-d electron excitations is available in the visible range. It is for this reason that transition metal ions have the property to absorb certain radiations from the visible region and exhibit the complementary colour.

Ask me for more details..........Reward me if I'm correct.

taruntanuj007

Yes i have read there r mainly 2 ways of getting colored compounds either compounnd has unpaired electrons which undergo d-d transitions or we have a charge transfer comples like KMnO4 which is purple despite Mn not having d electrons at all (+7). Actually electrons from O temporarly go to Mn and transcend back to O thus same principle of frequency lying in visible region and thus colored

smriti.mathur

In transition element ions with a partly filled d- shell , it is possible to promote electrons from one d level to another d level of higher energy. This corresponds to a fairly small energy difference, and so light is absorbed in the visible region ( the complementary colour light is transmitted). The colour of a transition metal complex is dependent on how big the energy difference is between the two d levels. This in turn depends on the nature of the ligand and on the type of complex formed.

The s- and p- block elements do not have a partially filled d shell so there cannot be any d-d transitions. The energy to promote an s or p electron to a higher energy level is much greater and corresponds to ultraviolet light being absorbed (its complementary colour being white). Thus compounds of s- and p- block elements are typically not coloured.

Jyothi

There are five d-orbitals. Their shapes are -


d_xy	d_xz	d_yz	d_x²-y²	d_z²

In an octahedral complex the ligands are arranged around a central metal ion along the x, y and z axes as shown below -

As can be seen the d_x²-y² and d_z² orbitals overlap with the positions of the six ligands. This raises their energy relative to the other three d-orbitals

The amount of splitting (DE) produced in a transition metal ions d-orbitals is affected by the ligand used in the complex. e.g.

As can be seen from the equation above substitution of four water molecules by ammonia molecules in the complex causes the wavelengths of light absorbed to change, therefore changing the colour.

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