Chemistry

14 d and f - block elements transition elementsThe complex ions which absorb light in the infrared or ultraviolet regions of the spectrumare colorless, e.g. (i) anhydrous cupric sulphate is colorless since it absorbs light in the infraredregion. (ii) [Cu(CN)4] 4- ion absorbs light in the ultraviolet region and hence is colorless.With the help of visible absorption spectrum of a complex ion it is possible to predict thecolor of the complex. For example, [Ti(H2O)6] 3+ ion shows absorption maxima at a wavelengthof about 5000Å which corresponds to the wave number v = 20000 cm -1 as shown below:Since 1Å =10 -8 cm. wavelength, λ= 5000Å =5000x10 -8 cmConsequently wave number,v = 1/λ=1/5000x10 -8=1/5x10 -5 cm -1 =0.2x10 5 cm -1 =20000cm -1Light of this wavelength (5000Å) isgreen (Fig 14.5) and is absorbed by thecomplex ion. Thus the transmitted light ispurple, which is in fact, the color of theions.79Quick QuizFig.14.101. Why do most of the transition metal ions posses a definite color?2. What is wavelength of green color3. When complex compound appear black4. What will be geometry of complex compound having co-ordination number 2, 4 and 6.5. Give examples of hexadentate and tridentate ligand.14.4 CHEMISTRY OF SOME IMPORTANT TRANSITION ELEMENTS14.4.1 VanadiumIn this topic we will discuss:i) The conversion between various Vanadium Oxidation states andii)The use of Vanadium (V) oxide as a catalyst in the contact process.Vanadium's Oxidation StatesVanadium has oxidation states in its compounds of +5, +4, +3 and +2. This section looksat ways of changing between them. It starts with a bit of description, and then goes on to look atthe reactions in terms of standard redox potentials (standard electrode potentials).