   Chapter 21, Problem 7RQ

Chapter
Section
Textbook Problem

# The crystal field model predicts magnetic properties of complex ions and explains the colors of these complex ions. How? Solutions of [Cr(NH3)6]Cl3 are yellow, but Cr(NH3)63+ does not absorb yellow light. Why? What color light is absorbed by Cr(NH3)63+? What is the spectrochemical series, and how can the study of light absorbed by various complex ions be used to develop this series? Would you expect Co(NH3)62+ to absorb light of a longer or shorter wavelength than Co(NH3)63+? Explain.

Interpretation Introduction

Interpretation: The reason for the crystal field model predicting the magnetic properties of the complex ions and the colors of the complex ions; the reason for the yellow color of Cr(NH3)3+ by not absorbing the yellow color; the meaning of the spectrochemical series and the reason for development of the spectrochemical series by the study of light absorbed by different complex ions; and comparison of the wavelength absorbed by Co(NH3)2+ with that by Co(NH3)3+ is to be stated.

Concept introduction: If the electrons in the hybridized orbital are all paired, the magnetic property of each electron is nullified by the magnetic field of its pair. Thus, the complex is repelled by the magnetic field and the complex is said to exhibit diamagnetism.

Coordination complex exhibits coloration due to dd transition of electrons.

The spectrochemical series is the series of the ligand arranged in the decreasing order of their ability to split the crystal field and absorb the equivalent energy for dd transition.

Ligands are the electron donating group, therefore, are attracted by the positively charged transition metal. Thus, more the oxidation number of a metal ion, more will be the strength of attraction of ligand and more will be the crystal field energy gap created by the ligand.

To determine: The reason for the crystal field model predicting the magnetic properties of the complex ions and the colors of the complex ions; the reason for the yellow color of Cr(NH3)3+ by not absorbing the yellow color; the meaning of the spectrocheminal series and the reason for development of the spectrochemical series by the study of light absorbed by different complex ions; and comparison of the wavelength absorbed by Co(NH3)2+ with that by Co(NH3)3+ .

Explanation

Explanation

The electrons exhibit magnetic property due to its charge and spin motion. Thus, a coordination complex exhibits magnetism arising from the electrons present in the hybridized orbitals of the complex.

If the electrons in the hybridized orbital are all paired, the magnetic property of each electron is nullified by the magnetic field of its pair. Thus, the complex is repelled by the magnetic field and the complex is said to exhibit diamagnetism.

If some of the electrons in the hybridized orbital are unpaired, the net magnetic property of the electrons due to its spin results the attraction of the complex by the magnetic field and the complex is said to be exhibit paramagnetism.

The strong ligands when binds to the transition metal ions to form coordination complex, it splits the energy of the dorbital into lower and higher energy level and the electrons excite from the lower to the higher energy level by absorption of visible light energy and emit the complementary energy. Thus, coordination complex exhibit coloration due to dd transition.

The color of coordination complex ion, Cr(NH3)3+ is yellow. Thus, the electrons Cr(NH3)3+ absorbs the complimentary light of yellow, that is violet, and excite to the higher energy level. While coming back to the lower energy level, the electrons emit yellow energy. Thus, the color of the complex visible is yellow.

The spectrochemical series is the series of the ligand arranged in the decreasing order of their ability to split the crystal field and absorb the equivalent energy for dd transition

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