Electron Configurations · Paper 1 — Free Chemistry HL Practice Questions

Phosphorus has atomic number 15 and electron configuration $1s^2\, 2p^6\, 3s^2\, 3p^3$. Using the Aufbau principle, Pauli exclusion principle, and Hund's rule, and filling the $3p$ orbitals in order of increasing $m_l$ $(-1, 0, +1)$, what are the quantum numbers $(n,\, l,\, m_s)$ of the last electron added?

A vanadium atom (atomic number 23) has the electron configuration $\text{[Ar] }4s^2\, 3d^3$. A student instead writes the configuration as $\text{[Ar] }3d^5$, keeping the total electron count correct. Which principle is most directly violated by the student's configuration?

The ground-state electron configuration of oxygen ($Z = 8$) is $\text{1s}^2\text{ 2p}^4$. How many unpaired electrons does an oxygen atom have in its ground state?

A neutral chromium atom (atomic number 24) has anomalous ground-state electron configuration. Which of the following correctly represents this configuration?