Textbook Question
Complete the exercises below. Draw the crystal-field energy-level diagrams and show the placement of electrons for each of the following complexes:
a. [VCl6]3–,
b. [FeF6]3– (a high-spin complex),
Ch.23 - Transition Metals and Coordination Chemistry
Chapter 23, Problem 62
Complete the exercises below. For each of the following metals, write the electronic configuration of the atom and its 3+ ion: c. Co. Draw the crystal-field energy-level diagram for the d orbitals of an octahedral complex, and show the placement of the d electrons for each 3+ ion, assuming a weak-field complex. How many unpaired electrons are there in each case?
Verified step by step guidance1
Step 1: Determine the atomic number of cobalt (Co), which is 27. This tells us that a neutral cobalt atom has 27 electrons.
Step 2: Write the electronic configuration for a neutral cobalt atom. Start by filling the lower energy orbitals first: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^7.
Step 3: To find the electronic configuration of the Co^{3+} ion, remove three electrons from the neutral atom's configuration. Electrons are removed first from the 4s orbital and then from the 3d orbital: Co^{3+} is 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6.
Step 4: Draw the crystal-field energy-level diagram for the d orbitals in an octahedral complex. In a weak-field complex, the five d orbitals split into two sets: t_{2g} (lower energy) and e_g (higher energy).
Step 5: Place the six d electrons of Co^{3+} in the t_{2g} and e_g orbitals according to Hund's rule and the weak-field assumption. Count the number of unpaired electrons in the configuration.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electronic Configuration
Electronic configuration describes the distribution of electrons in an atom's orbitals. For cobalt (Co), which has an atomic number of 27, the ground state electronic configuration is [Ar] 3d7 4s2. When cobalt forms a 3+ ion, it loses three electrons, typically from the 4s and 3d orbitals, resulting in the configuration [Ar] 3d6.
Recommended video:
Guided course
01:33
Electron Configuration Example
Crystal Field Theory
Crystal Field Theory (CFT) explains how the arrangement of ligands around a central metal ion affects the energy levels of its d orbitals. In an octahedral complex, the five d orbitals split into two energy levels: the lower-energy t2g (dxy, dyz, dzx) and the higher-energy eg (dx2-y2, dz2) orbitals. The extent of this splitting depends on the strength of the ligands, which can be classified as strong or weak field.
Recommended video:
Guided course
01:18The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
Unpaired Electrons and Magnetic Properties
The number of unpaired electrons in an atom or ion determines its magnetic properties. In the case of the Co3+ ion with a 3d6 configuration in a weak-field octahedral complex, the electrons will occupy the t2g orbitals first, leading to four unpaired electrons. This results in a paramagnetic behavior, as unpaired electrons contribute to the overall magnetic moment of the ion.
Recommended video:
Guided course
00:59Magnetic Quantum Example