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Questions and Answers
Which element exhibits the largest number of oxidation states?
Which element exhibits the largest number of oxidation states?
Which element usually does NOT show variable oxidation states?
Which element usually does NOT show variable oxidation states?
Which of the following elements has a negative M2+/M standard electrode potential, except for one?
Which of the following elements has a negative M2+/M standard electrode potential, except for one?
What is the main reason for the positive E° value of Cu compared to other elements?
What is the main reason for the positive E° value of Cu compared to other elements?
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Which trend is observed in M2+/M standard electrode potentials from Ti to Zn?
Which trend is observed in M2+/M standard electrode potentials from Ti to Zn?
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Which electron configuration contributes to the unexpected electrode potential for Mn?
Which electron configuration contributes to the unexpected electrode potential for Mn?
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What does the inability of Cu to liberate H2 from acids imply?
What does the inability of Cu to liberate H2 from acids imply?
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Which parameter does NOT influence the M2+/M standard electrode potential?
Which parameter does NOT influence the M2+/M standard electrode potential?
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Why does Sc have a very low standard electrode potential?
Why does Sc have a very low standard electrode potential?
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What explains the comparatively high electrode potential value for Mn?
What explains the comparatively high electrode potential value for Mn?
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What is the highest oxidation state represented in halides according to the trends?
What is the highest oxidation state represented in halides according to the trends?
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What factor contributes to the stabilization of the highest oxidation states in halides?
What factor contributes to the stabilization of the highest oxidation states in halides?
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Which metal has the extra stability of its +3 oxidation state compared to its +2 oxidation state?
Which metal has the extra stability of its +3 oxidation state compared to its +2 oxidation state?
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Why are the fluorides in low oxidation states unstable?
Why are the fluorides in low oxidation states unstable?
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What is true about manganese regarding its oxidation states in halides?
What is true about manganese regarding its oxidation states in halides?
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What does the electrode potential trend suggest about the stability of V2+?
What does the electrode potential trend suggest about the stability of V2+?
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What is the formula for calculating the magnetic moment based on the number of unpaired electrons?
What is the formula for calculating the magnetic moment based on the number of unpaired electrons?
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Which ion has the highest number of unpaired electrons according to the provided configurations?
Which ion has the highest number of unpaired electrons according to the provided configurations?
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Which statement is true regarding the magnetic moment and unpaired electrons?
Which statement is true regarding the magnetic moment and unpaired electrons?
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What happens when an electron from a lower energy d orbital is excited to a higher energy d orbital?
What happens when an electron from a lower energy d orbital is excited to a higher energy d orbital?
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Which ion configuration reflects no unpaired electrons?
Which ion configuration reflects no unpaired electrons?
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Which of the following ions show color due to the presence of unpaired electrons?
Which of the following ions show color due to the presence of unpaired electrons?
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Which statement correctly describes the effect of ligands on color formation in ions?
Which statement correctly describes the effect of ligands on color formation in ions?
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Which of the following ions has a calculated magnetic moment of 1.73 BM?
Which of the following ions has a calculated magnetic moment of 1.73 BM?
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Which of the following metal ions is colourless in aqueous solution?
Which of the following metal ions is colourless in aqueous solution?
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What characteristic property allows transition metals to form complex compounds?
What characteristic property allows transition metals to form complex compounds?
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Which transition metal is commonly used as a catalyst in the Haber process?
Which transition metal is commonly used as a catalyst in the Haber process?
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What type of compounds are formed when small atoms like H, C, or N are trapped inside metal crystal lattices?
What type of compounds are formed when small atoms like H, C, or N are trapped inside metal crystal lattices?
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Which of the following ions contributes to the formation of a yellow colour in aqueous solution?
Which of the following ions contributes to the formation of a yellow colour in aqueous solution?
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Which transition metal ion is associated with a violet colour in an aqueous solution?
Which transition metal ion is associated with a violet colour in an aqueous solution?
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What is a key feature of interstitial compounds compared to pure metals?
What is a key feature of interstitial compounds compared to pure metals?
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Which metal can show multiple oxidation states and thus act as an effective catalyst?
Which metal can show multiple oxidation states and thus act as an effective catalyst?
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Which arrangement does not represent the correct order of paramagnetic behaviour?
Which arrangement does not represent the correct order of paramagnetic behaviour?
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Which of the following ionic species will impart color to an aqueous solution?
Which of the following ionic species will impart color to an aqueous solution?
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Brass is an alloy primarily composed of which two elements?
Brass is an alloy primarily composed of which two elements?
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Which statement about interstitial compounds is incorrect?
Which statement about interstitial compounds is incorrect?
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Which of the following correctly describes the trend of ionic size from Ni2+ to Mn2+?
Which of the following correctly describes the trend of ionic size from Ni2+ to Mn2+?
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Which of the following elements has the lowest oxidation states?
Which of the following elements has the lowest oxidation states?
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What is the reason behind the lack of color in Zn2+, Cu+, and Ti4+?
What is the reason behind the lack of color in Zn2+, Cu+, and Ti4+?
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In the context of stability in aqueous solution, which is the correct trend?
In the context of stability in aqueous solution, which is the correct trend?
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Study Notes
Chemical Properties of d-Block Elements
-
Electrode Potentials and Chemical Reactivity
- All 3d series elements have negative M2+/M electrode potential except for Cu.
- This is related to thermodynamic parameters:
- Enthalpy of atomisation (ΔaH)
- First Ionisation Energy (IE1)
- Second Ionisation Energy (IE2)
- Enthalpy of hydration (ΔhydH)
- Cu has a positive value because its high energy for the transformation to Cu 2+(aq) is not balanced by its hydration enthalpy
- This means Cu cannot liberate H2 from acids
- E° value becomes less negative as we move from Ti to Zn.
- However, Mn, Zn and Ni have values that are more negative than expected.
- Mn - Due to 3d5 configuration.
- Zn - Due to 3d10 configuration.
- Ni - Due to the highest negative ΔhydH.
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Trends in the M3+/M2+ Standard Electrode Potentials
- Sc has a very low value reflecting the stability of Sc3+ (noble gas configuration).
- Zn has a high value due to the stable d10 configuration of Zn2+.
- The comparatively high value for Mn shows that Mn 2+(d5) is particularly stable.
- The comparatively low value for Fe shows the extra stability of Fe 3+ (d5).
- The comparatively low value for V is related to the stability of V 2+ (half-filled t2g level).
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Trends in Stability of Higher Oxidation States
- The highest oxidation numbers are achieved in TiX4 (tetrahalides), VF5 and CrF6.
- Mn does not have a +7 state in simple halides but MnO 3F is known.
- Beyond Mn, the only trihalides known are FeX’3 (X’ = F to Br) and CoF3.
- F can stabilise the highest oxidation state due to:
- Higher lattice energy (e.g. CoF3)
- Higher bond enthalpy terms in covalent compounds (e.g. VF5 and CrF6).
- For V+5, halides other than VF5 will hydrolyse to oxohalides (VOX3).
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Magnetic Properties
- The magnetic moment increases with the increasing number of unpaired electrons
- This provides information about the number of unpaired electrons in an atom, molecule, or ion
- Magnetic moment is measured in Bohr magnetons (BM)
- μ = n (n + 2), where n is the number of unpaired electrons.
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Formation of Coloured Ions
- When an electron from a lower energy d orbital is excited to a higher energy d orbital, this corresponds to the frequency of light absorbed.
- The frequency is usually in the visible region causing the complementary colour to be observed.
- The frequency of light absorbed is determined by the nature of the ligand.
- Water molecules act as ligands in aqueous solutions.
- Ions with no unpaired electrons are colourless.
- Colourless ions: Sc3+(3d0), Ti4+(3d0), Zn2+ (3d10)
- Violet ions: V2+ (3d3), Cr3+ (3d3), Mn3+ (3d4)
- Purple ions: Ti3+ (3d1)
- Pink ions: Mn2+ (3d5)
- Blue ions: V4+ (3d1), Cr2+ (3d4), Cu2+ (3d9)
- Yellow ions: Fe3+ (3d5)
- Bluepink ions: Co3+Co2+ (3d6, 3d7)
- Green ions: V3+ (3d2), Fe2+ (3d6), Ni2+ (3d8)
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Formation of Complex Compounds
- Complex compounds are those where metal ions bind to anions or neutral molecules.
- This results in complex species with unique properties.
- Examples: [Fe(CN)6]3–, [Fe(CN)6]4–, [Cu(NH3)4]2+ and [PtCl4]2–.
- Transition metals form many complex compounds due to:
- Smaller size of the metal ions
- High ionic charges
- Availability of d orbitals for bond formation.
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Catalytic Properties
- Transition metals and their compounds are catalysts due to their ability to:
- Adopt multiple oxidation states
- Form complexes.
- Examples:
- Vanadium(V) oxide (in Contact Process)
- Finely divided iron (in Haber’s Process)
- Nickel (in Catalytic Hydrogenation)
- This makes them more effective as catalysts because the transition metal ions can change their oxidation state.
- Example: Iron(III) catalyses the reaction between iodide and persulphate ions.
- 2I– + S2O82– → I2 + 2SO42–
- Reaction steps:
- 2Fe3+ + 2I– → 2Fe2+ + I2
- 2Fe2+ + S2O82– → 2Fe3+ + 2SO42–
- Transition metals and their compounds are catalysts due to their ability to:
-
Formation of Interstitial Compounds
- Interstitial compounds are formed when small atoms (H, C, or N) get trapped inside the crystal lattices of metals.
- They are typically non-stoichiometric and neither ionic nor covalent.
- Examples: TiC, Mn4N, Fe3H, VH0.56, TiH1.7, etc.
- They have high:
- Melting points (higher than pure metals)
- Hardness (some borides approach diamond in hardness)
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Summary of Key Facts and Trends
- Increasing Stability of Oxidation States: Ti (+4) < V (+5) < Cr (+6) < Mn (+7)
- Stability of +3 Oxidation State: Sc3+ > Cr3+ > Fe3+ > Co3+
- Paramagnetic Behaviour: Mn2+ > Fe2+ > Cr2+ > V2+
- Ionic Size: Mn2+ > Fe2+ > Co2+ > Ni2+
- Number of Oxidation States: Sc (+1) < Ti (+3) < Cr (+5) < Mn (+6)
- Coloured Ions: Ions with unpaired electrons are coloured.
- Interstitial Compounds: Formed when small atoms are trapped in the crystal lattices of metals, resulting in higher melting points and hardness than the pure metal.
- Catalytic Activity: Transition metals and their compounds are good catalysts due to their ability to change oxidation states and form complexes.
Quiz Questions and Solutions
-
Quiz 1: Which of the following exhibits the largest number of oxidation states?
- Answer: Mn (25).
- Explanation: Mn can have oxidation states from +2 to +7.
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Quiz 2: Which of the following elements usually does NOT show variable oxidation states?
- Answer: Sc (21).
- Explanation: Sc can only show a +3 oxidation state.
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Quiz 3: Which of the following arrangements does not represent the correct order of the property stated against it?
- Answer: A V2+ < Cr2+ < Mn2+ < Fe2+: paramagnetic behaviour
- Explanation: Mn2+ has the maximum number of unpaired electrons among these ions.
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Quiz 4: Which one of the following ionic species will impart colour to an aqueous solution?
- Answer: D Cr3+
- Explanation: Zn2+ {3d10}, Cu+ {3d10} and Ti4+ {3d0} have no unpaired electrons and are colorless.
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Quiz 5: Brass is an alloy of
- Answer: A Cu + Zn
- Explanation: Brass is an alloy of copper and zinc.
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Quiz 6: Which of the following statements about interstitial compounds is incorrect?
- Answer: D They are chemically reactive.
- Explanation: Interstitial compounds are known for their inertness and are not typically chemically reactive.
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Description
This quiz explores the chemical properties and electrode potentials of d-block elements, focusing on the 3d series. It examines the thermodynamic parameters that influence their reactivity, including ionization energies and hydration enthalpies. Test your understanding of these trends and the unique behavior of certain elements like Cu, Mn, Zn, and Ni.
