. a) Write the electron configuration for the Cu atom in condensed (noble gas) format.
b) The electron configuration for copper does not follow the expected trend based on the Aufbau principle. Briefly explain why this is the case. An orbital filling diagram will be useful in your explanation.
c) Which ion of Cu is present in the complexes synthesized in this experiment? Write the electron configuration for this ion.
d) Like most transition metals, copper can form multiple ions. Aside from the ion present in this experiment, there is one other very common ion of copper. Identify what ion this is, and briefly justify why you would expect this ion to be common for copper. An electron configuration and / or orbital filling diagram will be useful in your explanation.
The Correct Answer and Explanation is :
a) Electron configuration for the Cu atom in condensed (noble gas) format:
The atomic number of copper (Cu) is 29, so its full electron configuration is:
[ \text{Cu: [Ar]} 3d^{10} 4s^1 ]
The noble gas argon (Ar) has an atomic number of 18, so the condensed configuration is:
[ \text{Cu: [Ar]} 3d^{10} 4s^1 ]
b) Explanation for the electron configuration deviation from the expected trend:
The electron configuration for copper does not follow the simple Aufbau principle because of a phenomenon known as electron correlation and energy stabilization. According to the Aufbau principle, electrons should fill orbitals in order of increasing energy. The expected configuration for Cu would be ( 3d^9 4s^2 ), but instead, copper adopts the configuration ( 3d^{10} 4s^1 ), which involves the promotion of one electron from the ( 4s )-orbital to the ( 3d )-orbital.
This is explained by the fact that a fully-filled ( 3d^{10} ) orbital is particularly stable due to electron pairing, and the configuration ( 3d^{10} 4s^1 ) lowers the overall energy of the atom. The energy difference between the ( 4s ) and ( 3d ) orbitals is very small, making it energetically favorable for the electron to move from the ( 4s )-orbital to the ( 3d )-orbital, creating a completely filled ( 3d )-subshell, which is more stable than the alternative configuration.
The orbital filling diagram for copper would look like this:
- ( 4s ): One electron
- ( 3d ): Ten electrons
c) The ion of Cu present in the complexes synthesized in this experiment:
Copper typically forms two main oxidation states in its compounds: +1 and +2. For the complexes synthesized in this experiment, it is likely that copper is in the +2 oxidation state, as this is more common in many copper(II) complexes (e.g., copper sulfate, copper chloride, etc.).
When copper loses two electrons, its electron configuration changes. The ( 4s ) orbital, which is the highest energy orbital, loses both electrons, followed by one electron from the ( 3d )-orbital. Thus, the electron configuration for Cu²⁺ is:
[ \text{Cu}^{2+}: [Ar] 3d^9 ]
This leaves the copper ion with a partially filled ( 3d )-orbital, which is the stable configuration for Cu²⁺.
d) Another common ion of copper and justification:
Aside from the ( \text{Cu}^{2+} ) ion, copper can also form the Cu⁺ ion, which is the +1 oxidation state. The formation of the Cu⁺ ion is also common because when copper loses one electron, it reaches a stable electron configuration that closely resembles the electron configuration of a noble gas, argon (( [Ar] 3d^{10} )).
For the Cu⁺ ion, the electron configuration is:
[ \text{Cu}^+: [Ar] 3d^{10} ]
This configuration is more stable because the ( 3d )-subshell becomes completely filled, which provides a stable, low-energy configuration for the copper ion.
Why Cu⁺ is common: The Cu⁺ ion is particularly stable because the fully filled ( 3d^{10} ) configuration is energetically favorable. Additionally, the ( 4s^1 ) electron is loosely bound and can be easily removed, making Cu⁺ formation relatively easy. This explains why the +1 oxidation state is quite common for copper in certain compounds.