The expected electron configuration for copper should be [Ar]4s^2 3d^9. However, copper’s electron configuration is [Ar]4s^1 3d^10. Which of the following would provide experimental evidence of copper’s exception to the normal electron configuration?
A The mass spectrum of copper shows the different isotopes of copper.
B Copper ions in solution have color, which indicates that there are unpaired d orbital electrons.
C The photoelectron spectroscopy spectrum for copper shows the relative number of electrons in each orbit.
D Copper has the ability to form cations of plus one and plus two, whereas the other transition elements generally form cations of plus two and plus three.
The correct answer and explanation is :
The correct answer is C: The photoelectron spectroscopy spectrum for copper shows the relative number of electrons in each orbit.
Explanation:
The electron configuration of copper is an interesting case because, although the expected configuration based on the Aufbau principle would suggest [Ar] 4s² 3d⁹, copper instead adopts [Ar] 4s¹ 3d¹⁰. This occurs because of the stability that arises from a completely filled 3d subshell. The slight energy difference between the 4s and 3d orbitals allows copper to promote one electron from the 4s orbital to the 3d orbital, thus resulting in a more stable, fully filled 3d subshell.
Now, let’s explore the options:
- A: The mass spectrum of copper shows the different isotopes of copper.
This option is not directly related to electron configuration. The mass spectrum reveals the isotopic composition of copper, but it does not provide information about the arrangement of electrons in the atom. Therefore, this cannot be used to confirm the electron configuration exception. - B: Copper ions in solution have color, which indicates that there are unpaired d orbital electrons.
While it’s true that copper ions in solution often show color due to transitions of electrons in the d orbitals (e.g., Cu²⁺ ions), this fact does not directly prove the exception in copper’s electron configuration. It reflects the d-electron transitions, but it doesn’t necessarily confirm the specific configuration that copper adopts in its neutral state. - C: The photoelectron spectroscopy spectrum for copper shows the relative number of electrons in each orbit.
This is the best answer. Photoelectron spectroscopy (PES) provides detailed information about the binding energies of electrons in different orbitals. If we were to perform PES on copper, we would observe a higher binding energy for the electrons in the 3d orbitals compared to the 4s electrons. Additionally, PES would reveal that the 4s orbital has only one electron (rather than two), confirming the unusual electron configuration of [Ar] 4s¹ 3d¹⁰ instead of [Ar] 4s² 3d⁹. - D: Copper has the ability to form cations of plus one and plus two, whereas the other transition elements generally form cations of plus two and plus three.
While it is true that copper can form both Cu⁺ and Cu²⁺ ions, this fact is more about the ionization of copper and does not directly explain the electron configuration anomaly. The formation of Cu⁺ (with a 3d¹⁰ configuration) and Cu²⁺ (with a 3d⁹ configuration) reflects the removal of electrons, but it doesn’t directly confirm the filled 3d configuration in the neutral atom.
Thus, photoelectron spectroscopy provides the most direct evidence of copper’s electron configuration because it allows us to measure the electron energies and confirm that copper adopts the configuration [Ar] 4s¹ 3d¹⁰ rather than the expected [Ar] 4s² 3d⁹.