JAMB Chemistry 2013 Paper

Concept:Use the electron configuration and Hund’s rule to count unpaired electrons in the p-orbitals.Explanation:Fluorine has atomic number $9$, so its electron configuration is:$$1s^2\,2s^2\,2p^5$$The $2p$-subshell has three orbitals and contains $5$ electrons.According to Hund’s rule, electrons occupy each p-orbital singly before pairing.So the distribution is: $\uparrow\downarrow \quad \uparrow\downarrow \quad \uparrow$Only one p-orbital contains an unpaired electron.Answer:$1$ unpaired electron in the p-orbitals of a fluorine atom.