Chapter 21: Problem 50
The \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}^{3+}\) ion is diamagnetic, but \(\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}^{2+}\) is paramagnetic. Explain.
Short Answer
Expert verified
The \(\mathrm{Co}(\mathrm{NH}_{3})_{6}^{3+}\) ion is diamagnetic because there are no unpaired electrons in its d-orbitals, as all electrons are paired up in the t鈧俫 orbitals. On the other hand, \(\mathrm{Fe}(H_{2}O)_{6}^{2+}\) is paramagnetic due to the presence of four unpaired electrons in its d-orbitals, caused by the smaller splitting in the weaker ligand field of H鈧侽.
Step by step solution
01
Writing Electronic Configurations
First, write down the electronic configurations of the central metal ions, Cobalt (Co) and Iron (Fe), considering their respective oxidation states. For Co in \(\mathrm{Co}(\mathrm{NH}_3)_6^{3+}\), the oxidation state of Co is +3. For Fe in \(\mathrm{Fe}(H_2O)_6^{2+}\), the oxidation state of Fe is +2.
The electronic configuration of Co and Fe in their neutral states are:
Co: [Ar] 4s虏 3d鈦
Fe: [Ar] 4s虏 3d鈦
Now let's remove the appropriate number of electrons to obtain the electronic configurations of Co鲁鈦 and Fe虏鈦:
Co鲁鈦: [Ar] 3d鈦
Fe虏鈦: [Ar] 3d鈦
02
Analysing the Ligand Field in Octahedral Complexes
Now we need to understand the ligand field splitting in the octahedral complexes. The ligands surrounding the metal ions in both complexes cause the d-orbitals to split into two sets of different energies: three orbitals of lower energy (t鈧俫) and two orbitals of higher energy (e_g).
The strong field ligand, NH鈧, in Co complex results in a larger splitting, represented by 螖鈧 (crystal field splitting energy), causing electrons to first fill the lower energy t鈧俫 orbitals. On the other hand, H鈧侽 is a weaker field ligand in Fe complex leading to smaller splitting, represented by 螖鈧, such that electrons might not necessarily fill the lower t鈧俫 orbitals first.
03
Filling the Electrons in the Split Orbitals
Now, fill up the d-electrons with respect to the splitting of the ligand field and Hund's rule (keep electrons unpaired in degenerate orbitals until all orbitals are half-filled):
Co鲁鈦: In the octahedral complex, the t鈧俫 orbitals are completely filled and the e_g orbitals are empty: t鈧俫鈫戔啌 t鈧俫鈫戔啌 t鈧俫鈫戔啌 e_g鈫-- e_g鈫--
Fe虏鈦: In the octahedral complex, the t鈧俫 orbitals are half-filled and one of the e_g orbitals has an unpaired electron: t鈧俫鈫戔啌 t鈧俫鈫-- t鈧俫鈫-- e_g鈫-- e_g鈫--
04
Analyzing Magnetic Properties
Now, we can determine the magnetic properties of both complexes:
In \(\mathrm{Co}(\mathrm{NH}_3)_6^{3+}\) complex, all the electrons are paired up with no unpaired electrons in its d-orbitals: t鈧俫鈫戔啌 t鈧俫鈫戔啌 t鈧俫鈫戔啌 e_g鈫-- e_g鈫--. This complex is diamagnetic, having no unpaired electrons.
In \(\mathrm{Fe}(H_2O)_6^{2+}\) complex, there are four unpaired electrons in the d-orbitals: t鈧俫鈫戔啌 t鈧俫鈫-- t鈧俫鈫-- e_g鈫-- e_g鈫--. This complex is paramagnetic due to the presence of unpaired electrons.
In summary, the \(\mathrm{Co}(\mathrm{NH}_{3})_{6}^{3+}\) ion is diamagnetic because there are no unpaired electrons in its d-orbitals, while \(\mathrm{Fe}(H_{2}O)_{6}^{2+}\) is paramagnetic due to the presence of four unpaired electrons in its d-orbitals.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Electronic Configuration
Understanding electronic configurations is essential for predicting a chemical ion's behavior. Cobalt (Co) and Iron (Fe) serve as central metal ions in our example. Initially, consider their neutral states: Co is \[\text{[Ar] 4s}^2 \text{3d}^7\], and Fe is \[\text{[Ar] 4s}^2 \text{3d}^6\]. Electrons are removed corresponding to oxidation states to form \({\text{Co}^{3+}}\) and \({\text{Fe}^{2+}}\). This yields electronic configurations of Co鲁鈦 as \[\text{[Ar] 3d}^6\], and Fe虏鈦 as \[\text{[Ar] 3d}^4\] respectively.
In transition metals, configuration primarily affects magnetic and color properties. By analyzing the resulting configurations, we learn about electron distribution in d-orbitals. This distribution sets the stage for grasping how complex ions like \((\text{Co(NH}_3)_6^{3+})\) and \((\text{Fe(H}_2\text{O})_6^{2+})\) behave in terms of bonding and magnetism.
In transition metals, configuration primarily affects magnetic and color properties. By analyzing the resulting configurations, we learn about electron distribution in d-orbitals. This distribution sets the stage for grasping how complex ions like \((\text{Co(NH}_3)_6^{3+})\) and \((\text{Fe(H}_2\text{O})_6^{2+})\) behave in terms of bonding and magnetism.
Octahedral Complexes
In coordination chemistry, octahedral complexes feature prominently. An octahedral complex involves six ligands symmetrically arranged around a central metal ion. The geometric shape resembles an octahedron. For \(\text{Co(NH}_3)_6^{3+}\) and \(\text{Fe(H}_2\text{O})_6^{2+}\), ammonia and water act as ligands. They coordinate with Cobalt and Iron, respectively.
Such complexes are essential for demonstrating ligand behavior and its impact on metal ions. Ligands like NH鈧, termed "strong field," and H鈧侽, "weak field," directly influence electronic properties. Strong field ligands cause larger crystal field splitting, altering electronic configuration within the metal's d-orbitals.
The arrangement and nature of ligands are crucial; they dictate energy levels. Understanding octahedral complexes unravels complexities in predicting a compound鈥檚 reactivity and stability.
Such complexes are essential for demonstrating ligand behavior and its impact on metal ions. Ligands like NH鈧, termed "strong field," and H鈧侽, "weak field," directly influence electronic properties. Strong field ligands cause larger crystal field splitting, altering electronic configuration within the metal's d-orbitals.
The arrangement and nature of ligands are crucial; they dictate energy levels. Understanding octahedral complexes unravels complexities in predicting a compound鈥檚 reactivity and stability.
Magnetic Properties
Magnetic properties in metal complexes depend on unpaired electron numbers. Electrons can either pair up or remain unpaired, which determines a substance as diamagnetic or paramagnetic.
**Diamagnetic Complexes:** They have all electrons paired. This results in no net magnetic moment, meaning they aren't attracted to magnetic fields. For instance, \(\text{Co(NH}_3)_6^{3+}\) has all d-electrons paired, rendering it diamagnetic.
**Paramagnetic Complexes:** Contain unpaired electrons. These create a net magnetic moment, making them magnetically attracted. \(\text{Fe(H}_2\text{O})_6^{2+}\) contains four unpaired electrons. Consequently, it's paramagnetic.
The comparison highlights how the electronic distribution influenced by ligands determines if a complex is magnetically active or not.
**Diamagnetic Complexes:** They have all electrons paired. This results in no net magnetic moment, meaning they aren't attracted to magnetic fields. For instance, \(\text{Co(NH}_3)_6^{3+}\) has all d-electrons paired, rendering it diamagnetic.
**Paramagnetic Complexes:** Contain unpaired electrons. These create a net magnetic moment, making them magnetically attracted. \(\text{Fe(H}_2\text{O})_6^{2+}\) contains four unpaired electrons. Consequently, it's paramagnetic.
The comparison highlights how the electronic distribution influenced by ligands determines if a complex is magnetically active or not.
Crystal Field Splitting
Crystal field splitting occurs when ligands approach a metal ion, disrupting the uniform energy of its d-orbitals. This causes them to split into two groups of different energies; three lower (t鈧俫) and two higher (e_g).
In an octahedral complex, the extent of splitting (denoted as 螖鈧) preferences from weak to strong field ligands. \(\text{NH}_3\) results in significant splitting, promoting electron pairing at lower energy levels. Hence, \(\text{Co(NH}_3)_6^{3+}\) displays filled t鈧俫 and empty e_g. \(\text{H}_2\text{O}\), however, allows less splitting, leading to unpaired d-electrons appearing in both t鈧俫 and e_g orbitals, as in \(\text{Fe(H}_2\text{O})_6^{2+}\).
Recognizing these interactions between ligands and metal d-orbitals clarifies many properties seen in complexes. The magnitude of crystal field splitting affects color, magnetism, and overall stability.
In an octahedral complex, the extent of splitting (denoted as 螖鈧) preferences from weak to strong field ligands. \(\text{NH}_3\) results in significant splitting, promoting electron pairing at lower energy levels. Hence, \(\text{Co(NH}_3)_6^{3+}\) displays filled t鈧俫 and empty e_g. \(\text{H}_2\text{O}\), however, allows less splitting, leading to unpaired d-electrons appearing in both t鈧俫 and e_g orbitals, as in \(\text{Fe(H}_2\text{O})_6^{2+}\).
Recognizing these interactions between ligands and metal d-orbitals clarifies many properties seen in complexes. The magnitude of crystal field splitting affects color, magnetism, and overall stability.