Question

The electronic configuration of Cu (at.no. = 29) is

• A. $1s^2,2s^2 2p^6,3s^2 3p^6,4s^2, 3d^9$
• B. $1s^2, 2s^2 2p^6, 3s^2 3p^6 3d^{10}, 4s^1$
• C. $1s^2, 2s^2 2p^6, 3s^2 3p^6, 4s^2 4p^6, 5s^2 5p^1$
• D. $1s^2, 2s^2 2p^6, 3s^2 3p^6, 4s^2 4p^6, 3d^3$

Answer 1

The Correct Option is B

The task is to determine the correct electronic configuration for copper (Cu), whose atomic number is 29. This requires knowledge of how electrons are filled in the orbitals according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

Let's break this down step-by-step:

1. Understand the order of filling the orbitals: Electrons are filled in atomic orbitals following a specific order given by the Aufbau principle, which is based on increasing energy levels. The order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so forth.
2. Calculate the number of electrons: Copper has an atomic number of 29, which means 29 electrons must be placed in orbitals.
3. Fill the orbitals:
   • First, fill the 1s orbital with 2 electrons: 1s^2.
   • Next, fill the 2s orbital with 2 electrons: 2s^2.
   • Then, fill the 2p orbital with 6 electrons: 2p^6.
   • Continue filling the 3s orbital with 2 electrons: 3s^2.
   • Fill the 3p orbital with 6 electrons: 3p^6.
   • Move to the 4s orbital and fill it with 1 electron. Normally, this would be 2 electrons, but copper is an exception: 4s^1.
   • Finally, fill the 3d orbital with the remaining 10 electrons: 3d^{10}.

This results in the electronic configuration 1s^2, 2s^2 2p^6, 3s^2 3p^6 3d^{10}, 4s^1, which matches option two.

The reason the configuration is 3d^{10}, 4s^1 rather than 3d^9, 4s^2 is due to the stability gained by having a completely filled d-orbital. Copper prefers a full 3d subshell as it imparts greater stability over having a full 4s orbital.

Thus, the correct answer is: 1s^2, 2s^2 2p^6, 3s^2 3p^6 3d^{10}, 4s^1.