//M0//QN1//CS//DL0

Lanthanoid elements are classified by their 4f energy levels. They are extremely similar in properties. As the atomic number increases, the atomic and ionic radii decrease due to lanthanoid contraction from lanthanum to lutetium, and basicity also decreases. The sum of the three ionization enthalpies for each element is low, resulting in a predominant

+3 oxidation state. Ln3+ dominates the chemistry of these elements. Ln2+ and Ln4+ ions are always less stable than Ln3+. Inner orbital 4f electrons do not participate in bonding; they are neither removed nor significantly contribute to crystal field stabilization in complexes.(a) Which of the following is the most basic?

(A) Ce(OH)3 (B) Lu(OH)3
(C) Yb(OH)3 (D) Tb(OH)3
(b) In which of the following lanthanoids is the

+

2 oxidation state the most stable?
(A) Ce (B) Eu (C) Tb (D) Dy
(c) The colour of the trivalent ions of lanthanoids is due to:
(A) Lanthanoid contraction
(B) Their fluorescent properties
(C) The number of unpaired electrons in the

4f orbital

(D) The similar +3 oxidation state
(d) Lanthanoids are ________.
(A) the 14 elements of the sixth period (atomic numbers 90 to 103) that fill the 4f subshell.
(B) the 14 elements of the seventh period (atomic numbers 90 to 103) that fill the 5f subshell.
(C) the 14 elements of the sixth period (atomic numbers 58 to 71) that fill the 4f subshell.
(D) the 14 elements of the seventh period (atomic numbers 58 to 71) that fill the 4f subshell.

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(a) (A) Ce(OH)3
The atomic number increases, the ionic radii decrease due to lanthanoid contraction, and basicity also decreases. Therefore, Ce(OH)3 is the most ionic and the most basic.
(b) (B) Eu
While +3 is the predominant state, Europium (Eu) can achieve a stable +2 state. This is because the electronic configuration of Eu 2+ is [Xe] 4 f 7.
(c) (C) The number of unpaired electrons in the
4 f orbital
The color of lanthanoid ions (Ln 3+) is primarily due to f−f transitions. Because the 4 f subshell is partially filled with unpaired electrons, these electrons can absorb specific wavelengths of visible light to jump between different 4 f energy levels.
(d) (C) the 14 elements of the sixth period (atomic numbers 58 to 71) that fill the 4 f subshell.
Lanthanoids are the 14 elements of the sixth period (atomic numbers 58 to 71) that fill the 4 f subshell.

//M0//QN2//CS//DL0//EQ

All transition elements are metals and are therefore good conductors of electricity and heat. The melting and boiling points of transition elements are generally very high. Most transition elements melt above 1000°C, with a few exceptions. Transition metals have high enthalpy of atomization, which increases with an increase in the number of d- electrons and then decreases. This behaviour can also be explained based on increasing interatomic interactions with the increasing number of electrons.(a) Among the first transition series (atomic numbers 21 to 30), which element has the lowest enthalpy of atomization?

(A) Sc (B) Mn (C) Cu (D) Zn
(b) Which electronic configuration show the highest magnetic moment?
(A) 3 d 2 (B) 3 d 5 (C) 3 d 7 (D) 3 d 9
(c) The metallic character of transition elements is:
(A) more than alkali metals
(B) less than alkali metals
(C) same as alkali metals
(D) not fixed
(d) Which group of transition elements has nearly the same atomic size?
(A) Sc, Ti, V (B) Ni, Cu, Zn
(C) Fe, Co, Ni (D) V, Ni, Cu

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(a) (D) Zn
Zinc (Zn) has an electronic configuration of [Ar]3d 10 4s 2. Since all its d-orbitals are completely filled, there are no unpaired d-electrons to participate in metallic bonding.
(b) (B) 3 d 5
μ = , where n is the number of unpaired electrons.
3d 5: 5 unpaired electrons (n)
μ =
μ ≈ 5.92 BM
(c) (B) Less than alkali metals
Due to the presence of d-electrons and stronger effective nuclear charge, transition metals generally show less metallic character than alkali metals.
(d) (C) Fe, Co, Ni
In a transition series, the atomic radius initially decreases but then becomes almost constant in the middle of the series. For the elements Fe, Co, and Ni, the increasing nuclear charge is almost perfectly balanced by the increasing screening effect of the
d-electrons.

//M0//QN3//CS//DL0

A metallurgical research institute is developing high strength alloy material for aircraft engines. For this purpose, they search transition metals such as Cr, Mn, Fe, Co, Ni and their ions. During analysis they observe:

Many transition metal show multiple oxidation states.
Ions like MnO–4, Cr2O2–7 exhibit strong oxidizing properties
Coloured compounds form due to d-d transitions.
Complex formation tendency varies across the series.
To select the best alloying element, scientists measure the following oxidation states in real samples: Element Observed oxi n states Chromium (Cr) +2, +3, +6 Manganese (Mn) +2, +4, +7 Iron (Fe) +2, +3 Cobalt (Co) +2, +3(a) Which element in the table show the maximum number of oxidation states? Explain the reason.(b) Which metal ion from the list will form the strongest coordination complexes and why?(c) Between MnO 4– and Cr 2 O 2–7, Which is the strongest oxidizing agent? Justify answer using oxidation states.(d) Explain why transition metal compounds are often colored, using Fe 2+/Fe 3+ as an example.

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(a) Mn shows the highest variation: +2, +4, +7
Reason: It has h alf-filled 3 d 5 configuration, allowing oxidation from +2 to +7 by losing both 3 d and 4 s electrons.
(b) Cobalt (Co 3+) forms strongest complexes.
Reason: High charge density → strong ligand attraction → stable octahedral complexes.
Ex. [Co(NH 3)6]3+
(c) MnO 4– is the strongest oxidizing agent
Reason: Mn is in +7 oxidation state (higher oxidation state than Cr 6+ in Cr 2 O 7 2–).
Higher oxidation state → greater ability to accept electrons.
(d) Transition metals show colour due to d–d electronic transitions.
Ex. Fe 2+ (d 6) and Fe 3+ (d 5) absorb different wavelengths → appear green/yellow → characteristic colours.

//M0//QN4//CS//DL0//EQ

A company producing permanent magnets studies the magnetics behavior of transition metals. They analyze ions of Fe, Co, Ni and Cu to understand which metal ions have:

Maximum unpaired electrons
Highest paramagnetic character
Strong orbital contribution to magnetism
Stable metallic bonding for magnet development
Magnetic moment: µ = = BM Electronic Configurations: Fe 2+ → 3 d 6 Ni 2+ → 3 d 8 Co 2+ → 3 d 7 Cu 2+ → 3 d 9(a) Calculate the magnetic moment of Fe 2+, Co 2+, Ni 2+, Cu 2+.(b) Which metal ion is the most paramagnetic and

why?

(c) Why do transition metals form strong metallic bond?(d) Explain why Cu 2+ is coloured but Cu+ is colourless.

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(a) Fe 2+ → 3 d 6 → 4 unpaired e–
µ = = = 4.90 BM
Co 2+ → 3 d 7 → 3 unpaired e–
µ = = = 3.87 BM
Ni 2+ → 3 d 8 → 2 unpaired e–
µ = = = 2.83 BM
Cu 2+ → 3 d 9 → 1 unpaired e–
µ = = = 1.73 BM
(b) Fe 2+ is most paramagnetic because of 4 unpaired electrons.
(c) Due to presence of delocalized d-electrons, giving : High cohesive energy, strong metallic bonding, high melting point.
(d) Cu 2+ (d 9) → has one unpaired electron → d - d transitions → coloured.

//M0//QN5//CS//DL0//EQ

Cu+ (d 10) → No unpaired electron → No d - d transition → colourless.

Class 12 Chemistry (Part 1) 019
d-Block Elements: Periodic table elements where (n−1)d orbitals are progressively filled (Groups 3–12). Known as transition elements.
f-Block Elements: Elements in which 4f or 5f orbitals are progressively filled. Divided into lanthanoids and actinoids.
Transition Metals: Metals having incomplete d-subshells in atoms or common ions. Show characteristics like coloured ions, variable oxidation states, catalysis, etc.
Inner Transition Metals: f-block elements (lanthanoids + actinoids).
Electronic Configuration: Arrangement of electrons in orbitals; basis for classifying d- and f-block elements.
3 d/4 d/5 d/6 d Series: Four horizontal rows of transition metals based on the filling of d-orbitals.
Exceptional Configurations: Cases like Cr (3d 54s 1), Cu (3d 104s 1), Pd (4d 105s 0) due to stability of half-filled or fully filled orbitals.
Lanthanoids (Ln): Series from Ce to Lu, involving progressive filling of 4f orbitals. Show lanthanoid contraction.
Actinoids: Series from Th to Lr, involving progressive filling of 5f orbitals. Show multiple oxidation states and radioactivity.
Lanthanoid Contraction: Steady decrease in atomic/ionic radii from La to Lu due to poor shielding of 4f electrons.
Actinoid Contraction: Similar decrease across the actinoid series due to poor shielding in

5f orbitals.

Oxidation State: Charge of an atom in a compound; transition metals show a wide range due to variable d-electron participation.
Variable Oxidation States: Ability of transition metals to show many oxidation states (e.g., Mn: +2 to +7).
Standard Electrode Potential (E°): Measure of tendency of an element to get reduced. Governs redox behaviour of transition metals.
M 2+/M Potential: Standard reduction potential for M2+ → M; used to compare reactivities across transition series.
Ionisation Enthalpy: Energy required to remove electrons; increases across a transition series but less steeply than in main groups.
Atomic Radius: Distance from nucleus to valence shell; decreases gradually across the d-block due to poor d-electron shielding.
Ionic Radius: Radius of the ion; decreases with increasing charge and atomic number in a series.
Enthalpy of Atomisation: Energy required to convert atoms of a metal into gaseous state; high for transition metals due to strong metallic bonding.
Metal–Metal Bonding: Formation of bonds between metal atoms; stronger and more common in heavier transition metals (4d, 5d).
Coloured Ions: Transition ions show colour due to d–d transitions when electrons absorb visible light.
Paramagnetism: Magnetic behaviour due to unpaired electrons; measured using spin only formula .
Diamagnetism: Weak repulsion from magnetic fields due to absence of unpaired electrons.
Ferromagnetism: Strong attraction to magnetic fields; pronounced in elements like Fe, Co, Ni.
d–d Transitions: Electron jumps from lower to higher d-orbitals in complexes; cause colours in transition metal ions.
Crystal Field Theory (CFT): Theory explaining splitting of d-orbitals in complexes (connected to colours and magnetism).
Complex Compounds: Species where metal ions bind ligands to form coordinate complexes (e.g., [Fe(CN)6]3–).
Ligands: Ions/molecules that donate lone pairs to metals in complexes.
Coordination Number: Number of ligand donor atoms attached to central metal.
Catalytic Activity: Transition metals catalyse due to variable oxidation states and ability to form complexes.
Interstitial Compounds: Compounds where small atoms (H, C, N) occupy spaces in metal lattices (e.g., TiC, Fe₃H).
Alloys: Mixtures of metals forming solid solutions (e.g., brass, bronze, stainless steel).
Chromate Ion (CrO 4 2–): Tetrahedral ion; yellow; forms in alkaline medium.
Dichromate Ion (Cr 2 O 7 2–): Orange ion; dominant in acidic medium; strong oxidising agent.
Potassium Dichromate (K 2 Cr 2 O 7): Important oxidising agent, used in volumetric analysis and organic chemistry.
Permanganate Ion (MnO 4–): Purple ion; strong oxidising agent in acidic medium, weaker in neutral/alkaline media.
Potassium Permanganate (KMnO 4): Strong oxidant used in analysis, organic synthesis, and bleaching.
Manganate Ion (MnO 4 2–): Green ion; paramagnetic; disproportionates in neutral/acidic medium.
Oxide Formation: Transition metals form oxides across various oxidation states from +2 to +7 depending on element.
Oxocations: Metal cations with oxygen (VO2+, VO2+, TiO2+), stabilising higher oxidation states.
Disproportionation: Process where the same element is simultaneously oxidised and reduced. Example: Mn(VI) → Mn(VII) + Mn(IV).
Lanthanide Contraction Effect: Causes elements like Zr and Hf to have nearly identical radii and similar properties.
Radioactivity (Actinoids): Many actinoids are radioactive, forming multiple oxidation states and complex ions.
Nuclear Fuels: Actinoids like U and Pu used due to their fission properties.

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(no answer)