Questions and Answers
Which ion is coloured, Cu+ or Cu2+?
Cu+ is coloured
Cu2+ is paramagnetic but Cu+ is diamagnetic. Explain.
Cu2+ is paramagnetic and Cu+ is diamagnetic because Cu2+ contains an unpaired electron in its 3d orbital, while Cu+ has a fully filled d-subshell with no unpaired electrons.
Which of the two, ferrous or ferric ion has a larger magnetic moment?
Fe3+ has a larger magnetic moment.
What are d-block elements also known as?
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How many series are the transition elements classified into based on the (n-1) d-subshell?
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All d-block elements are transition elements. (True/False)
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Zinc, cadmium, and mercury are not regarded as ______________ elements.
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What is the exceptional electronic configuration of Chromium?
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What is the chemical equation for the oxidation of potassium iodide to iodine using potassium permanganate in acidic medium?
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What is the product of the oxidation of ferrous sulphate to ferric sulphate using potassium permanganate?
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What is the balanced chemical equation for the oxidation of hydrogen sulphide to sulfur with potassium permanganate in acidic medium?
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Which of the following statements is true about the oxidising properties of potassium permanganate?
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Why do lanthanoids form fewer complexes compared to transition elements?
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Lanthanoids are generally more reactive than transition elements.
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What are lanthanoids extracted as?
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In misch metals, ______ are the main lanthanoids present, making up approximately 94-95% of the mixture.
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Match the following uses with the corresponding lanthanoid compounds:
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Why are metals soft and have low melting and boiling points?
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Explain the trend in ionisation enthalpy across a transition series.
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What contributes to the high ionisation enthalpy values of Chromium and Copper?
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Why are the first ionisation enthalpies of elements in the third transition series higher than those in the first and second transition series?
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Explain why Ni(II) compounds are more stable than Pt(II) compounds.
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Why do Mn2+ and Zn2+ have more negative values for standard reduction potentials than expected?
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Why are most of the compounds of transition metals coloured?
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Why are transition metal ions with fully filled d-subshells colourless?
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Explain why Ti3+ is coloured (purple) while Ti4+ is colourless.
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Study Notes
D-Block Elements (Transition Elements)
- Definition: Elements that have incompletely filled d-orbitals in their ground state or in any one of their commonly occurring oxidation states.
- Classification: Four series based on the (n-1) d-subshell that gets filled:
- First transition series (3d-series): Sc to Zn (21 to 30)
- Second transition series (4d-series): Y to Cd (39 to 48)
- Third transition series (5d-series): La to Hg (57 to 80)
- Fourth transition series (6d-series): Ac to Cp (89 to 112)
Electronic Configuration of Transition Elements
- General outer electronic configuration: (n-1)d1-10ns1-2
- Exceptions:
- Chromium and copper have anomalous electronic configurations due to increased stability of half-filled and fully-filled d-orbitals
- Palladium has no electron in its ns subshell ([Kr] 4d10 5s0)
General Characteristics of Transition Elements
- All are metals with typical metallic properties (high melting and boiling points, high tensile strength, malleability, ductility, metallic lustre, high thermal and electrical conductivity)
- First ionisation energies are higher than s-block elements but lesser than p-block elements
- Electropositive in nature
- Most form coloured compounds
- Good tendency to form complexes
- Exhibit several oxidation states
- Generally paramagnetic in nature
- Form several alloys with other metals
- Form interstitial compounds with elements like hydrogen, boron, carbon, nitrogen, etc.
- Many are used as good catalysts
Atomic Radii of Transition Elements
- Intermediate between s-block and p-block elements
- Decrease with increase in atomic number within a series
- Decrease becomes smaller after mid-way in each series due to increased shielding effect of (n-1) d-electrons
- Atomic radii increase on moving down a group due to increase in the number of electronic shells
Ionic Radii of Transition Elements
- Follow the same trend as atomic radii
- Decrease with increase in nuclear charge for the same oxidation state
- Decrease with increase in oxidation state
Metallic Character of Transition Elements
- Due to low ionisation energies, presence of unpaired electrons, and vacant orbitals in their outermost shell
- Strength of metallic bonds depends on the number of unpaired electrons
Density of Transition Elements
- High density due to close-packed structures
- Increase with increase in atomic number within a series
- Increase on moving down a group due to increase in atomic mass and decrease in atomic radii
Melting and Boiling Points of Transition Elements
- Very high due to strong metallic bonds
- Increase up to the middle of a series and then decrease due to decrease in the number of unpaired electrons
- Exception: Mn and Te have lower melting points due to complicated lattice structures
Ionisation Enthalpies/Energies of Transition Elements
- First ionisation enthalpy increases with increase in atomic number within a series
- Increase is not very regular due to shielding effect of (n-1) d-electrons
- Chromium and copper have exceptionally high ionisation enthalpy values due to extra stability of half-filled and fully-filled d-subshells
- First ionisation enthalpies of elements of third transition series are higher than those of first and second transition series due to filled 4f orbitals
Standard Electrode Potentials (Standard Reduction Potentials)
- No regular trend in E0 (M2+/M) values
- Depend on ionisation enthalpies, sublimation enthalpy, and enthalpy of hydration
- If E0 (M2+/M) is high, M2+ ions are less stable than M
- If E0 (M2+/M) is low, M2+ ions are more stable than M
Oxidation States of Transition Elements
- Most exhibit variable oxidation states
- +1 and +2 oxidation states involve participation of ns electrons
- Higher oxidation states involve participation of both ns and (n-1) d electrons
- Maximum oxidation state increases with atomic number within a group
- Highest oxidation state shown by any transition element is eight (Ru and Os)### Relative Stability of Oxidation States
- The standard electrode potential value (E0) determines the stability of an element in a particular oxidation state in an aqueous medium.
- A greater negative (or lesser positive) value of E0 indicates greater stability of the element in that oxidation state.
Crystal Field Splitting
- A d-subshell consists of five orbitals: dxy, dxz, dyz, dx2-y2, and dz2.
- These orbitals are degenerate, but under the influence of combining anions or neutral molecules, they split into two groups: t2g and eg orbitals.
- The t2g group consists of dxy, dyz, and dxz orbitals, while the eg group consists of dx2-y2 and dz2 orbitals.
d-d Transition
- The electronic transition from lower energy d-orbitals to higher energy d-orbitals by the absorption of light energy of suitable wavelength is known as d-d transition.
- This transition is responsible for the color of transition metal ions.
Colored Ions
- Most transition metal ions are colored due to d-d transitions taking place between the split d-orbitals.
- The color of the ion depends on the wavelength of light absorbed, and the remaining wavelengths are transmitted, resulting in a complementary color.
Paramagnetic Properties
- Most transition elements and their compounds are paramagnetic in nature due to the presence of unpaired electrons in the (n-1)d orbitals.
- The magnetic character is expressed in terms of magnetic moment, which increases with the number of unpaired electrons.
Catalytic Properties
- Transition metals and their compounds act as catalysts for a number of chemical reactions due to:
- Presence of vacant d-orbitals
- Ability to exhibit variable oxidation states
- Tendency to form complexes
- These factors allow transition metals to form unstable reaction intermediates with reactants, providing an alternate path of lower activation energy and increasing the rate of the reaction.
Complex Formation
- Transition metal ions have a high tendency to form complexes due to:
- Small size of transition metal ions
- High nuclear charge
- Availability of vacant d-orbitals to accommodate lone pair of electrons donated by ligands
Alloy Formation
- Transition metals form alloys among themselves due to their similar atomic size, allowing atoms of one metal to substitute atoms of another metal in its crystal lattice.
Interstitial Compounds
- Transition metals form interstitial compounds with elements such as H, B, C, and N, which occupy the vacant spaces in the lattice of transition metals to form hard and rigid compounds.
- These compounds have altered physical properties, such as density, rigidity, hardness, malleability, ductility, and electrical conductivity, compared to the parent transition metals.
Important Compounds of Transition Metals
- Potassium dichromate (K2Cr2O7): prepared from chromite ore, FeO.Cr2O3, and used as an oxidizing agent.
- Potassium permanganate (KMnO4): prepared from pyrolusite, MnO2, and used as a powerful oxidizing agent in acidic, alkaline, and neutral media.
Potassium Dichromate
- Preparation: involves the conversion of chromite ore into sodium chromate, then acidifying it to form sodium dichromate, and finally reacting it with potassium chloride to form potassium dichromate.
- Oxidizing character: in acidic medium, it liberates nascent oxygen and acts as a strong oxidizing agent, oxidizing KI to iodine, Fe2+ to Fe3+, H2S to sulfur, and SO2 to H2SO4.
- Effect of pH: chromate ion and dichromate ion exist in equilibrium and are interconvertible by changing the pH of the solution.
Potassium Permanganate
- Preparation: involves the conversion of pyrolusite ore to potassium manganate, then oxidizing it to potassium permanganate using chlorine or ozone.
- Oxidizing properties: in acidic, alkaline, and neutral media, it liberates nascent oxygen and acts as a powerful oxidizing agent, oxidizing KI to iodine, Fe2+ to Fe3+, H2S to sulfur, and SO2 to H2SO4.
- Uses: as an oxidizing agent, in volumetric analysis for the estimation of Fe2+ and I- ions, and in dyeing and tanning.### Potassium Permanganate (KMnO4)
- KMnO4 is reduced to MnO2 and takes 3 moles of electrons to produce 3 gram equivalents of oxygen
- Equivalent weight of KMnO4 in neutral medium is 52.67
- KMnO4 is used as an oxidizing agent, disinfectant, and germicide
- It is used in volumetric analysis for the estimation of ferrous ion, oxalic acid, and oxalate ion
- Dilute alkaline KMnO4 solution (Baeyer's reagent) is used to identify unsaturated compounds in organic chemistry
F-Block Elements (Inner Transition Elements, Rare Earth Elements)
- F-block elements are those in which the last electron enters the f-orbital of their pre-penultimate or anti-penultimate shell
- General electronic configuration: (n-2)f1-14 (n-1)d⁰-Ins2
- F-block elements consist of two series of elements placed at the bottom of the periodic table
- Lanthanoids (first inner transition series) include the 14 elements of the 6th period from cerium (58) to lutetium (71)
- Actinoids (second inner transition series) include the 14 elements of the 7th period from thorium (90) to lawrencium (103)
Lanthanoids
- Lanthanoids follow lanthanum in the periodic table and have similar physical and chemical properties
- Electronic configuration: 4f1-14 5d⁰ 6s2
- Lanthanoids exhibit a stable +3 oxidation state, and some show +2 and +4 oxidation states
- Lanthanoid metal ions in +2 oxidation states are not very stable and act as good reducing agents
- Lanthanoid metal ions in +4 oxidation states are not very stable and act as good oxidizing agents
- Most lanthanoid metal atoms and ions are paramagnetic due to the presence of unpaired electrons
- La3+ and Lu3+ are diamagnetic due to the absence of unpaired electrons
- Colours of tri-positive ions of lanthanoids are due to f-f transitions
- Lanthanoid ions having f0, f7, and f14 configurations are colourless
- Lanthanoid contraction: slow and steady decrease in atomic size and ionic size of lanthanoids with increase in atomic number
- Cause of lanthanoid contraction: poor shielding effect of 4f electrons, leading to an increase in effective nuclear charge
- Consequences of lanthanoid contraction:
- Atomic size of elements of 2nd and 3rd transition series are almost same
- Basic character of hydroxides of lanthanides decreases from cerium to lutetium
- Lanthanides are very difficult to separate from their mixtures
- Yttrium (Y) occurs with heavy lanthanoids like Holmium and Erbium
- Lanthanoids form only a few complexes compared to transition elements due to larger size and unavailability of f orbitals for hybridization
- Chemical reactivity: lanthanoids are generally more reactive than transition elements
- Uses of lanthanoids: extracted as mixtures or alloys known as Misch metals, used for making tracer bullets, shells, flints for lighters, and parts of jet engines
Actinoids
- Actinoids are the 14 elements of the 7th period from thorium (90) to lawrencium (103)
- General electronic configuration: 5f1-14 6d⁰-I7s2
- Actinoids exhibit a stable +3 oxidation state, and some show +2, +4, +5, +6, and +7 oxidation states
- Actinoids show a greater number of oxidation states compared to lanthanoids due to the participation of 5f, 6d, and 7s orbitals in bond formation
- Actinoids exhibit paramagnetic properties
- Actinoids are all radioactive
- Uses of actinoids:
- U-233, U-235, and Pu-239 are used as fuel in nuclear reactors
- ThO2 mixed with 1% CeO2 is used for making incandescent gas mantles
- Thorium salts are used for the treatment of cancer
Comparison of Lanthanoids and Actinoids
- Similarities:
- Most common oxidation state is +3
- Involves the filling of (n-2)f orbitals
- Exhibit decrease in atomic radii and ionic radii with increase in atomic number
- Show paramagnetic properties
- Nitrates, sulphates, and perchlorates are soluble in water, and carbonates, hydroxides, and fluorides are insoluble in water
- Differences:
- Lanthanoids show fewer oxidation states compared to actinoids
- Lanthanoids are non-radioactive (except Promethium) while actinoids are all radioactive
- Lanthanoids do not form complexes easily, while actinoids form complexes easily
- Paramagnetism can be easily explained in lanthanoids, but not in actinoids
- Hydroxides of lanthanoids are less basic, while those of actinoids are more basic
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Test your knowledge of inorganic chemistry, including the properties of copper ions, magnetic moments of ferrous and ferric ions, and characteristics of d-block elements.
