9701 · 9.3
Chemical periodicity of other elements flashcards
Revision flashcards for Cambridge 9701 Chemical periodicity of other elements (syllabus 9.3). Flip, recall, then mark a real past-paper question.
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What is the definition of a transition element?
A d-block element that forms at least one stable ion with a partially filled d sub-shell.
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Why is Zinc (Zn) not considered a transition element?
Zinc only forms the $Zn^{2+}$ ion, which has a full d sub-shell with the electronic configuration $[Ar] 3d^{10}$. It does not have a partially filled d sub-shell.
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Why is Scandium (Sc) not typically considered a transition element?
Scandium only forms the $Sc^{3+}$ ion, which has an empty d sub-shell with the electronic configuration $[Ar]$. It does not form a stable ion with a partially filled d sub-shell.
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Explain why transition elements have variable oxidation states.
The energies of the 4s and 3d sub-shells are very close. This allows for the loss of a variable number of electrons from both sub-shells, leading to different stable oxidation states.
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What are the two common oxidation states of iron?
Iron(II) ($Fe^{2+}$) and Iron(III) ($Fe^{3+}$).
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Why are compounds of transition elements often coloured?
In the presence of ligands, the d-orbitals split into two different energy levels. Electrons can be promoted from the lower to the higher level by absorbing energy from visible light. The colour we see is the complementary colour to the light absorbed.
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Why are compounds of $Zn^{2+}$ and $Sc^{3+}$ colourless?
$Zn^{2+}$ has a full d sub-shell and $Sc^{3+}$ has an empty d sub-shell. Therefore, no d-d electron transitions can occur by absorbing visible light.
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What is the catalyst used in the Haber process, and what is the equation?
Catalyst: Iron (Fe). Equation: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.
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What is the catalyst used in the Contact process, and what is the key step it catalyses?
Catalyst: Vanadium(V) oxide ($V_2O_5$). It catalyses the oxidation of sulfur dioxide to sulfur trioxide: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$.
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How does the trend in atomic radius for transition elements in Period 4 compare to the trend across Period 3?
Across Period 3, atomic radius decreases significantly due to increasing nuclear charge. Across the Period 4 transition metals, the atomic radius remains relatively constant because the extra nuclear charge is shielded by the inner 3d electrons.
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What is a ligand?
A molecule or ion that donates a lone pair of electrons to a central metal ion to form a dative covalent (coordinate) bond.
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What colour is the aqueous copper(II) ion, $[Cu(H_2O)_6]^{2+}$?
Blue. It absorbs light from the orange/red part of the spectrum.