9701 · 28.1
General physical and chemical properties of the first row of transition elements, titanium to copper flashcards
Revision flashcards for Cambridge 9701 General physical and chemical properties of the first row of transition elements, titanium to copper (syllabus 28.1). 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-subshell.
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Why is Scandium (Sc) not considered a transition element?
Scandium only forms one stable ion, Sc³⁺, which has an electronic configuration of [Ar] 3d⁰. Its only stable ion has an empty d-subshell, not a partially filled one.
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Why is Zinc (Zn) not considered a transition element?
Zinc only forms one stable ion, Zn²⁺, which has an electronic configuration of [Ar] 3d¹⁰. Its only stable ion has a full d-subshell, not a partially filled one.
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Why do transition elements exhibit variable oxidation states?
The energy difference between the 4s and 3d subshells is very small. Consequently, successive ionisation energies increase steadily, allowing for the removal of a variable number of electrons.
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What is required for a transition metal complex to be coloured?
1. A partially filled d-subshell. 2. The presence of ligands to cause d-orbital splitting.
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Explain the origin of colour in transition metal complexes.
Ligands split the d-orbitals. Electrons absorb energy from visible light to be promoted from a lower to a higher energy d-orbital (d-d transition). The colour observed is the complementary colour to the light absorbed.
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Why are aqueous solutions of Zn²⁺ ions colourless?
The Zn²⁺ ion has a full d-subshell ([Ar] 3d¹⁰). Since there are no empty spaces for electrons to be promoted into, d-d transitions cannot occur, and no visible light is absorbed.
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What is a complex ion?
A central metal ion bonded to one or more molecules or ions called ligands by coordinate (dative covalent) bonds.
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How do transition elements act as heterogeneous catalysts? Give an example.
They provide an active surface where reactants can adsorb. Their available d-orbitals form weak bonds, increasing reactant concentration and weakening covalent bonds. Example: Iron (Fe) in the Haber process.
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How do transition elements act as homogeneous catalysts? Give an example.
They can change oxidation state to provide an alternative reaction pathway with a lower activation energy. Example: Fe²⁺ ions catalysing the reaction between I⁻ and S₂O₈²⁻.
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Describe the trend in atomic radius across the first row of transition elements (Ti to Cu).
The atomic radius shows a slight decrease and then remains relatively constant. The increasing nuclear charge is largely offset by the poor shielding effect of the added 3d electrons.
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What is the electronic configuration of the Cu²⁺ ion?
[Ar] 3d⁹. Remember to remove electrons from the 4s subshell first, then the 3d. For Cu atom ([Ar] 3d¹⁰4s¹), remove the 4s¹ electron, then one 3d electron.