Chapter 6: Problem 91
Explain why the ground-state electron configurations of \(\mathrm{Cr}\) and \(\mathrm{Cu}\) are different from what we might expect.
Short Answer
Expert verified
Cr and Cu have electron configurations favoring half/full d subshells for enhanced stability.
Step by step solution
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chromium
Chromium (
Cr
), a fascinating transition metal, presents an interesting twist in its electron configuration. According to the general rules, we would expect chromium to have an electron configuration of
[Ar] 3d^4 4s^2
. However, the reality differs slightly. The actual ground-state configuration is
[Ar] 3d^5 4s^1
.
Why does this happen? Chromium prefers to move one electron from the 4s orbital to the 3d subshell. This adjustment achieves a half-filled 3d^5 configuration, which provides added stability. The stability arises due to reduced electron-electron repulsions and increased exchange energy, making the half-filled state more favorable energetically.
This reconfiguration helps chromium retain its unique properties and contributes to its fascinating chemistry and application in various materials.
Why does this happen? Chromium prefers to move one electron from the 4s orbital to the 3d subshell. This adjustment achieves a half-filled 3d^5 configuration, which provides added stability. The stability arises due to reduced electron-electron repulsions and increased exchange energy, making the half-filled state more favorable energetically.
This reconfiguration helps chromium retain its unique properties and contributes to its fascinating chemistry and application in various materials.
Copper
Copper (
Cu
) is another intriguing element with an unexpected electron configuration. Normally, with copper, you'd expect to see
[Ar] 3d^9 4s^2
. However, copper adopts an actual configuration of
[Ar] 3d^{10} 4s^1
.
The key reason for this shift is the quest for a filled 3d subshell. By transferring one electron from the 4s orbital to complete the 3d subshell, copper achieves a 3d^{10} configuration. This configuration is energetically more favorable, as a filled 3d level significantly enhances stability.
This electron movement reflects copper's adaptability and its use in electrical applications and alloys, highlighting its importance in technology and engineering.
The key reason for this shift is the quest for a filled 3d subshell. By transferring one electron from the 4s orbital to complete the 3d subshell, copper achieves a 3d^{10} configuration. This configuration is energetically more favorable, as a filled 3d level significantly enhances stability.
This electron movement reflects copper's adaptability and its use in electrical applications and alloys, highlighting its importance in technology and engineering.
3d subshell
The
3d
subshell plays a critical role in understanding the nuances of electron configurations in transition metals like chromium and copper. Typically, d subshells can hold up to 10 electrons, and the stability comes into play especially when they are half-filled (
3d^5
) or fully filled (
3d^{10}
).
When an element like chromium exhibits a 3d^5 configuration, it enjoys a symmetrical electron arrangement, reducing repulsion among electrons and increasing exchange energy. Similarly, copper stabilizes with a completely filled 3d^{10} subshell, which also minimizes electronic interactions driving the element to a lower energy state.
When an element like chromium exhibits a 3d^5 configuration, it enjoys a symmetrical electron arrangement, reducing repulsion among electrons and increasing exchange energy. Similarly, copper stabilizes with a completely filled 3d^{10} subshell, which also minimizes electronic interactions driving the element to a lower energy state.
- 3d subshells offer unique configurations with enhanced stability.
- Characteristics of 3d subshells affect chemical properties.
- Understanding these configurations helps predict reactivity.
Aufbau principle
The Aufbau principle is a fundamental guideline used to determine the electron configuration of an atom. It suggests that electrons fill up atomic orbitals of progressively increasing energy levels, starting with the lowest. This is often known as the "building-up" principle.
The principle implies an order: filling starts from the 1s orbital, proceeding through 2s , 2p , 3s , 3p , 4s , and then 3d . However, transition metals like chromium and copper present deviations from this principle. These exceptions occur because a half-filled or fully filled 3d subshell provides more stability by lowering electron interactions and achieving a balanced state.
Although the Aufbau principle is a good starting point, it’s essential to keep in mind exceptions, especially in transition metals. Understanding these exceptions provides insight into the intricate workings of electron configurations.
The principle implies an order: filling starts from the 1s orbital, proceeding through 2s , 2p , 3s , 3p , 4s , and then 3d . However, transition metals like chromium and copper present deviations from this principle. These exceptions occur because a half-filled or fully filled 3d subshell provides more stability by lowering electron interactions and achieving a balanced state.
Although the Aufbau principle is a good starting point, it’s essential to keep in mind exceptions, especially in transition metals. Understanding these exceptions provides insight into the intricate workings of electron configurations.
