Problem 25
Question
Which one of the following ions is colourless in its aqueous solution? (a) \(\mathrm{Ti}^{3+}\) (b) \(\mathrm{Cu}^{2+}\) (c) \(\mathrm{Ni}^{2+}\) (d) \(\mathrm{Zn}^{2+}\)
Step-by-Step Solution
Verified Answer
(d) \(\mathrm{Zn}^{2+}\) is colorless in its aqueous solution.
1Step 1: Understanding the Role of d-Electrons
Transition metal ions display colors due to the d-electron configuration. When light passes through the aqueous solution, certain wavelengths are absorbed for d-d transitions, often resulting in a colored appearance.
2Step 2: Analyzing the Electron Configuration of Each Ion
1. x2922Ti^{3+}x2922: Has one electron in the 3d subshell, which can undergo d-d transitions, making it appear colored.
2. x2922Cu^{2+}x2922: Has a partially filled d subshell (3d^9), which allows for d-d transitions, resulting in a color.
3. x2922Ni^{2+}x2922: Has a partially filled d subshell (3d^8), which can also result in a color.
4. x2922Zn^{2+}x2922: Has a completely filled 3d subshell (3d^10), which prevents d-d transitions, making it typically colorless.
3Step 3: Concluding the Color of each Ion Based on Electron Configuration
Since x2922Zn^{2+}x2922 has a fully filled d-shell (3d^10), it does not have the possibility for d-d transitions as these transitions require unpaired d-electrons. This results in a colorless aqueous solution.
Key Concepts
d-Electron Configurationd-d TransitionsColor of IonsElectron Configuration Analysis
d-Electron Configuration
The d-electron configuration is crucial in determining the properties and behaviors of transition metal ions. Transition metals are defined by their ability to form ions with partially filled d-subshells. These d-electrons play a significant role in various chemical phenomena.
For example, the electronic configuration of a transition metal like zinc for - \Zn would be: \([ \text{Ar} ] 3d^{10} 4s^2\) in its elemental state- In the \(\mathrm{Zn}^{2+}\) ion, it loses two electrons, resulting in a configuration of \([ \text{Ar} ] 3d^{10}\)
Having a complete d-subshell, as seen in \( \mathrm{Zn}^{2+} \), can influence the ion's chemical reactivity and optical properties. For instance, the absence of unpaired d-electrons in \( \mathrm{Zn}^{2+} \) leads to specific optical behavior and reactivity compared to ions with incomplete d subshells, like \( \mathrm{Cu}^{2+} \) or \( \mathrm{Ni}^{2+} \). This difference in electron configurations is foundational to understanding their properties.
For example, the electronic configuration of a transition metal like zinc for - \Zn would be: \([ \text{Ar} ] 3d^{10} 4s^2\) in its elemental state- In the \(\mathrm{Zn}^{2+}\) ion, it loses two electrons, resulting in a configuration of \([ \text{Ar} ] 3d^{10}\)
Having a complete d-subshell, as seen in \( \mathrm{Zn}^{2+} \), can influence the ion's chemical reactivity and optical properties. For instance, the absence of unpaired d-electrons in \( \mathrm{Zn}^{2+} \) leads to specific optical behavior and reactivity compared to ions with incomplete d subshells, like \( \mathrm{Cu}^{2+} \) or \( \mathrm{Ni}^{2+} \). This difference in electron configurations is foundational to understanding their properties.
d-d Transitions
d-d transitions refer to the phenomena where electrons in a partially filled d-orbital gain energy and jump to a higher energy d-orbital. This process is common in transition metal ions with unpaired d-electrons. Transition metal ions absorb specific wavelengths of light which correspond to the energy difference between these d orbitals.
These transitions occur primarily in ions with:- Partially filled d-orbitals For instance, analyzing the ion \( \mathrm{Cu}^{2+} \), we find that it has one more favorable condition for these transitions. It extracts energy from visible light, facilitating d-electron transitions between different d-orbitals. This absorbed light subsequently leads to the ion exhibiting various colors.
On the other hand, \( \mathrm{Zn}^{2+} \), with a full \( 3d^{10} \) configuration possesses no unpaired electrons, hence is incapable of undergoing d-d transitions. This immobilizes the possibility for color formation, rendering zinc ions generally colorless.
These transitions occur primarily in ions with:- Partially filled d-orbitals For instance, analyzing the ion \( \mathrm{Cu}^{2+} \), we find that it has one more favorable condition for these transitions. It extracts energy from visible light, facilitating d-electron transitions between different d-orbitals. This absorbed light subsequently leads to the ion exhibiting various colors.
On the other hand, \( \mathrm{Zn}^{2+} \), with a full \( 3d^{10} \) configuration possesses no unpaired electrons, hence is incapable of undergoing d-d transitions. This immobilizes the possibility for color formation, rendering zinc ions generally colorless.
Color of Ions
The color of transition metal ions in aqueous solutions is largely attributed to their d-electron configurations and the resulting d-d transitions. The absorption of light at particular wavelengths results in the complementary color being observed.
Key points influencing ion color include:- The presence of unpaired electrons in the d-orbitals.- The specific wavelengths absorbed by the particular electron transitions.When \(\mathrm{Ni}^{2+} \) with its \(3d^8\) configuration absorbs light, it shows a characteristic green or blue color. Similarly,\( \mathrm{Ti}^{3+} \), with its one electron in the d-shell, tends to show a purple hue due to its specific absorption pattern.
Colorlessness, as seen in \( \mathrm{Zn}^{2+} \), stems from the absent d-d transitions due to a fully filled 3d subshell hindering the capacity to alter electron energy levels. Thus, the absence of light absorption in the visible spectrum results in a clear, colorless presentation.
Key points influencing ion color include:- The presence of unpaired electrons in the d-orbitals.- The specific wavelengths absorbed by the particular electron transitions.When \(\mathrm{Ni}^{2+} \) with its \(3d^8\) configuration absorbs light, it shows a characteristic green or blue color. Similarly,\( \mathrm{Ti}^{3+} \), with its one electron in the d-shell, tends to show a purple hue due to its specific absorption pattern.
Colorlessness, as seen in \( \mathrm{Zn}^{2+} \), stems from the absent d-d transitions due to a fully filled 3d subshell hindering the capacity to alter electron energy levels. Thus, the absence of light absorption in the visible spectrum results in a clear, colorless presentation.
Electron Configuration Analysis
Performing an electron configuration analysis is essential to predict the behavior and properties of ions. Here’s a simplified approach for determining configurations and understanding their implications.1. **Identify the neutral atom's electron configuration:**- Consider zinc (Zn) with an atomic number of 30: \([ \text{Ar} ] 3d^{10} 4s^2 \)
2. **Determine the charge and resulting configuration of the ion:**- For \( \mathrm{Zn}^{2+} \): Removing two electrons results in \( [ \text{Ar} ] 3d^{10} \)
3. **Analyze the impact of electron arrangements:**- Unpaired electrons facilitate d-d transitions, allowing vibrant colors in aqueous solutions.- The absence of partially filled d-orbitals, as in \( \mathrm{Zn}^{2+} \), eliminates these transitions, leading to colorlessness.
Understanding electron configurations enables predictions about color, chemical reactivity, and magnetic properties of transition metal ions.
2. **Determine the charge and resulting configuration of the ion:**- For \( \mathrm{Zn}^{2+} \): Removing two electrons results in \( [ \text{Ar} ] 3d^{10} \)
3. **Analyze the impact of electron arrangements:**- Unpaired electrons facilitate d-d transitions, allowing vibrant colors in aqueous solutions.- The absence of partially filled d-orbitals, as in \( \mathrm{Zn}^{2+} \), eliminates these transitions, leading to colorlessness.
Understanding electron configurations enables predictions about color, chemical reactivity, and magnetic properties of transition metal ions.
Other exercises in this chapter
Problem 22
In the extraction of zinc, the formation of blue flame is due to the burning of (a) \(\mathrm{C}\) (b) \(\mathrm{CO}\) (c) \(\mathrm{Zn}\) (d) \(\mathrm{ZnO}\)
View solution Problem 23
Which one of the following ions exhibits colour in aqueous solution? (a) \(\mathrm{Ti}^{4+}\) (b) \(\mathrm{Zn}^{2+}\) (c) \(\mathrm{Ni}^{2+}\) (d) \(\mathrm{Sc
View solution Problem 26
Which one of the following ions exhibit highest magnetic moment? (a) \(\mathrm{Cu}^{2+}\) (b) \(\mathrm{Ti}^{3+}\) (c) \(\mathrm{Ni}^{2+}\) (d) \(\mathrm{Mn}^{2
View solution Problem 27
Which one of the following is a diamagnetic ion? (a) \(\mathrm{Cu}^{2+}\) (b) \(\mathrm{Mn}^{2+}\) (c) \(\mathrm{S} \mathrm{c}^{3+}\) (d) \(\mathrm{Co}^{2+}\)
View solution