Home / AS & A Level Chemistry 1.3 Electrons, energy levels and atomic orbitals Exam Style Practice Questions Paper 1
What is the electrons in boxes notation for the \(\mathrm{Fe^{3+}}\) ion?
Correct Answer: \( \boxed{\mathrm{D}} \)
The electronic configuration of iron is:
\(\mathrm{Fe:[Ar]\,3d^6\,4s^2}\)
When forming \(\mathrm{Fe^{3+}}\), the two electrons are removed from the \(4s\) orbital first, followed by one electron from the \(3d\) subshell:
\(\mathrm{Fe^{3+}:[Ar]\,3d^5}\)
According to Hund’s rule, the five \(3d\) orbitals each contain one unpaired electron and the \(4s\) orbital is empty.
Therefore, the correct answer is (D).
What is the electronic configuration for the particle \(^{27}_{13}\mathrm{Al}^{+}\)?
Correct Answer: \( \boxed{\mathrm{B}} \)
Aluminium has atomic number \(13\), so a neutral aluminium atom has the electronic configuration \(1\mathrm{s}^2\,2\mathrm{s}^2\,2\mathrm{p}^6\,3\mathrm{s}^2\,3\mathrm{p}^1\).
Forming \(\mathrm{Al}^{+}\) removes one electron from the outermost \(3\mathrm{p}\) orbital.
Therefore, the electronic configuration becomes
\(1\mathrm{s}^2\,2\mathrm{s}^2\,2\mathrm{p}^6\,3\mathrm{s}^2\)
Therefore, the correct answer is (B).
Which graph represents the number of unpaired electrons in the atoms of six elements in Period 3 of the Periodic Table?
Correct Answer: \( \boxed{\mathrm{D}} \)
The six Period 3 elements with proton numbers \(13\) to \(18\) are:
The pattern is:
\(1 \rightarrow 2 \rightarrow 3 \rightarrow 2 \rightarrow 1 \rightarrow 0\)
This increases to a maximum at phosphorus and then decreases to zero at argon, matching graph D.
Therefore, the correct answer is (D).