Question

Which of the following electron configurations is not possible?
A.$2p^{6}$
B.$3s^{1}$
C.$2p^{5}$
D.$3f^{12}$

Answer 1

Hint: The electronic configuration describes the filling of the electrons in different orbitals. The electrons are filled in the orbitals according to the Aufbau principle.

Complete answer:
- The electronic configuration is a representation of the arrangement of electrons distributed among the shells and subshells in the orbitals of an atom.
- It is generally used to describe the electronic arrangement in the orbitals of an atom in its ground state.
- The filling of electrons in the orbitals relative to its energy level, to attain stable configuration of element.
- The Aufbau principle states that electrons always arrange in an order starting from orbitals that have low energy to highly energized orbitals.
- The Aufbau principle describes the model building in atoms by progressively adding electrons, starting that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels.
- Since the third energy level can have s, p, and d orbitals only, the electronic configuration of $3f^{12}$ is not possible.

Therefore, the answer to the question is option (D).

Note:
The energy of the 3d orbital is lower than the 4s orbital, still the electrons occupy the 4s orbital first before 3d orbital. This is because the 3d electrons are found closer to the nucleus and hence, they repel each other more strongly.