Guidance for Orbital-Filling Diagram Question (Ground State of Oxygen)

Q15. Which orbital-filling diagram represents the ground state of oxygen?

Background

Topic: Electron Configuration and Orbital-Filling Diagrams

This question tests your understanding of how electrons fill atomic orbitals according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle. You need to identify the correct electron configuration for oxygen in its ground state.

Key Terms and Concepts:

• Aufbau Principle: Electrons fill the lowest energy orbitals first.

• Hund's Rule: Electrons occupy orbitals singly before pairing up.

• Pauli Exclusion Principle: No two electrons in an atom can have the same set of quantum numbers; each orbital can hold two electrons with opposite spins.

• Electron Configuration for Oxygen: Oxygen has 8 electrons. The ground state configuration is $1s^2\ 2s^2\ 2p^4$.

Step-by-Step Guidance

1. Recall that oxygen has 8 electrons. Start by filling the lowest energy orbitals first: $1s^2$ (not shown in the diagrams, but implied by [He] core), then $2s^2$, then $2p^4$.

2. For the $2p$ orbitals, distribute 4 electrons according to Hund's rule: place one electron in each of the three $2p$ orbitals before pairing up.

3. Check each diagram for the correct number of electrons in $2s$ (should be 2, paired) and $2p$ (should be 4: two paired, two unpaired).

4. Look for the diagram where the $2s$ orbital is fully paired, and the $2p$ orbitals have two paired electrons and two unpaired electrons, following Hund's rule.

Try solving on your own before revealing the answer!

Final Answer: Diagram C (third image) represents the ground state of oxygen.

In Diagram C, the $2s$ orbital is fully paired, and the $2p$ orbitals have four electrons distributed according to Hund's rule: two paired and two unpaired. This matches the ground state configuration for oxygen.