Comprehensive Study Notes on D and F Block Elements

Overview of the Periodic Table

• The Periodic Table is organized into several blocks: the S-block, the P-block, the D-block, and the F-block.

• The S-block and P-block elements are not the focus of this study guide.

• The D-block elements are located between the S-block and the P-block in Groups 3 to 12.

• The F-block contains two series of 14 elements each, which are extracted from the main body of the table and placed at the bottom. These are known as the Lanthanide ($Ln$) and Actinide ($An$) series.

• The series within the F-block are also referred to as the $4f$ series and the $5f$ series.

The D-Block Elements (Transition Metals)

• General Classification: Elements from Groups 3 to 12 are known as D-block elements because their last electron enters the $(n-1)d$ subshell.

• Transition Elements: D-block elements are called transition elements because they lie between the S and P blocks. However, Group 12 ($Zn, Cd, Hg$) and Group 3 ($Sc$ etc.) are often distinguished because they do not always exhibit the typical variable oxidation states or unpaired electrons characteristic of other transition metals. Specifically, Group 12 elements have a completely filled $d$-orbital ($d^{10}$).

• Series in D-Block: The D-block is divided into four series based on the $(n-1)d$ orbital being filled ($n$ represents the period number):

  • 3D Series ($n=4$): Atomic numbers $21$ to $30$ ($Sc$ to $Zn$).

  • 4D Series ($n=5$): Atomic numbers $39$ to $48$ ($Y$ to $Cd$).

  • 5D Series ($n=6$): Atomic numbers $57$ to $80$ (including a gap for lanthanides).

  • 6D Series ($n=7$): Atomic numbers $89$ to $112$.

• Group and Orbital Relation: D-block elements span 10 groups (3 to 12). Since the $d$-subshell contains 5 orbitals, it can accommodate a maximum of $10$ electrons, corresponding to these 10 groups.

• Electronic Configuration Exceptions: There are many exceptions in electronic configurations due to the very small energy difference between the $(n-1)d$ and $ns$ subshells. For example, in the $3d$ series, Chromium ($Cr$, $Z=24$) and Copper ($Cu$, $Z=29$) are well-known exceptions.

Physical and Chemical Properties of D-Block Elements

• Hardness and Volatility: Transition metals are generally very hard and possess low volatility.

• Melting and Boiling Points: These elements have high melting and boiling points. The melting point typically reaches a maximum at the $d^5$ configuration because the number of unpaired electrons is at its maximum, leading to stronger inter-atomic bonding.

• Enthalpy of Atomization: They possess high enthalpies of atomization. The enthalpies for the second ($4d$) and third ($5d$) series are higher than those of the first ($3d$) series.

• Oxidation States:

  • Transition elements show variable oxidation states, with the exception of the first and last members of a series ($Sc$ and $Zn$ in the $3d$ series).

  • Scandium ($Sc$) always shows a $+3$ oxidation state. Due to a small energy gap, it easily loses two electrons from $4s$ and one from $3d$.

  • Oxidation states generally increase from Scandium ($Z=21$) to Manganese ($Z=25$), reaching a maximum of $+7$ for $Mn$. After Manganese, the states decrease as electrons start pairing in the $d$-orbitals.

  • Stability is highest at $d^0$, $d^5$ (half-filled), and $d^{10}$ (completely filled) configurations.

  • Lower oxidation states (e.g., $Mn^{2+}$) tend to be alkaline/basic, while higher oxidation states (e.g., $Mn^{6+}$) tend to be acidic. Middle oxidation states are often amphoteric.

• Ionization Enthalpy: Their ionization energy lies between the S and P blocks. It generally increases along a series due to increasing effective nuclear charge. The ionization energies of the $5d$ series are significantly higher than those of the $3d$ and $4d$ series.

• Atomic and Ionic Sizes: Moving from left to right, the atomic size initially decreases because the effective nuclear charge ($Z_{eff}$) dominates over the shielding effect. This decrease continues until approximately Group 10. Afterward, the size may increase slightly as the shielding effect of the $(n-1)d$ electrons begins to dominate the effective nuclear charge.

• Standard Electrode Potential ($E^\circ$): Most transition metals, except for Copper ($Cu$), have a standard electrode potential less than Hydrogen ($E^\circ_{H^+/H_2} = 0.00\,V$). Consequently, they can release $H_2$ gas from dilute acids.

Magnetic and Color Properties of Transition Elements

• Origin of Magnetism: Magnetic properties arise from two types of electron motion: orbital motion and spin motion.

• Types of Magnetism:

  • Paramagnetism: Exhibited by substances with unpaired electrons. Most transition metal ions are paramagnetic.

  • Diamagnetism: Exhibited by substances where all electrons are paired. These are usually colorless.

  • Ferromagnetism: A strong form of magnetism found in elements like Iron ($Fe$) that retain magnetic properties even after the external field is removed.

• Color Formation: Transition metal ions are often colored due to the presence of unpaired electrons and $d-d$ transitions. These electrons absorb specific wavelengths of visible light to move from lower energy $d$-orbitals to higher energy ones. The reflected light corresponds to the complementary color (e.g., absorbing yellow results in a purple appearance).

Interstitial Compounds and Alloys

• Interstitial Compounds: Transition metals can trap small non-metal atoms like Hydrogen ($H$), Boron ($B$), Carbon ($C$), or Nitrogen ($N$) in the spaces (interstices) of their crystal lattices.

  • These compounds are typically non-stoichiometric.

  • They are harder than pure metals and have higher melting points.

  • They remain chemically inert.

• Alloys: Because transition metals have similar atomic sizes, they can easily replace each other in a crystal lattice to form alloys.

  • Examples include Steel, Brass (Copper and Zinc), and Bronze (Copper and Tin).

  • Alloys are generally harder and have higher melting points than the constituent pure metals.

The F-Block Elements (Inner Transition Metals)

• Definition: F-block elements have their valence electrons entering the $(n-2)f$ orbital. They are also known as Rare Earth Metals.

• Series: There are two series of 14 elements each:

  • Lanthanides ($4f$ Series): Follow Lanthanum ($Z=57$).

  • Actinides ($5f$ Series): Follow Actinium ($Z=89$).

• Inclusion of $La$ and $Ac$: Although Lanthanum ($La$) and Actinium ($Ac$) technically belong to the D-block, they are studied with the F-block due to strong similarities in properties.

Lanthanides (4f Series)

• Atomic Range: Strictly defined as Cerium ($Ce, Z=58$) to Lutetium ($Lu, Z=71$).

• Electronic Configuration: $[Xe] 4f^{1-14} 5d^{0-1} 6s^2$.

• Radioactivity: Only Promethium ($Pm$) is radioactive; the rest are non-radioactive.

• Properties:

  • The common oxidation state is $+3$.

  • Cerium can show $+4$ because it reaches the stable $4f^0$ configuration.

  • Stability is high at $4f^0, 4f^7$, and $4f^{14}$.

  • Lanthanide ions are colored due to unpaired electrons.

• Lanthanide Contraction: The steady decrease in atomic and ionic radii from left to right in the series is caused by the poor shielding effect of $4f$ electrons, which allows the increased nuclear charge to pull the electron cloud inward.

• Chemical Reactions: Lanthanides react with Sulfur to form Sulfides, with Acids to release $H_2$, with Halogens to form Halides, and with Oxygen to form Oxides.

• Uses: Used in air jets, Misch metal, lasers, and as catalysts in petroleum cracking ($CePO_4$).

Actinides (5f Series)

• Atomic Range: Thorium ($Th, Z=90$) to Lawrencium ($Lr, Z=103$).

• Electronic Configuration: $[Rn] 5f^{1-14} 6d^{0-1} 7s^2$.

• General Properties: All actinides are radioactive. They are silvery-white metals.

• Actinide Contraction: Similar to lanthanide contraction, there is a decrease in size along the series. However, the actinide contraction is greater than the lanthanide contraction because the shielding by $5f$ electrons is even poorer than that by $4f$ electrons.

• Oxidation States: They show more variable oxidation states than lanthanides ($+3, +4, +5, +6$) because the energy difference between $5f, 6d$, and $7s$ levels is very small.

• Uses:

  • Thorium ($Th$): Used in cancer treatment and gas mantles.

  • Uranium ($U$): Used as nuclear fuel and in glass/textile industries.

  • Plutonium ($Pu$): Used in nuclear reactors and atomic bombs.

Comparison Between Lanthanides and Actinides

• Similarities:

  • Both show a common $+3$ oxidation state.

  • Both are electropositive and act as strong reducing agents.

  • Both form colored ions and are paramagnetic.

  • Both exhibit contraction (Lanthanide vs. Actinide).

• Differences:

  • Lanthanides show states of $+2, +3, +4$; Actinides show up to $+6$.

  • Only Promethium is radioactive in Lanthanides; all Actinides are radioactive.

  • Lanthanides have simpler magnetic properties; Actinides have complex ones.

Potassium Dichromate ($K_2Cr_2O_7$)

• Preparation: Prepared from chromite ore ($FeCr_2O_4$). It involves forming Sodium Chromate, then Sodium Dichromate, and finally reacting with Potassium Chloride to get $K_2Cr_2O_7$.

• Properties: Orange-red crystalline solid. Moderately soluble in cold water, highly soluble in hot water. Insoluble in alcohol.

• Structures:

  • Chromate Ion ($CrO_4^{2-}$): Tetrahedral structure.

  • Dichromate Ion ($Cr_2O_7^{2-}$): Two tetrahedra sharing one oxygen atom with a $Cr-O-Cr$ bond angle of $126^\circ$.

• Oxidizing Nature: It is a powerful oxidizing agent in acidic media.

  • Standard Reaction: $Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O$

  • Example (Iodide to Iodine): $Cr_2O_7^{2-} + 6I^- + 14H^+ \rightarrow 2Cr^{3+} + 3I_2 + 7H_2O$

• Uses: Used in volumetric analysis (titrations), leather tanning, and as a cleaning agent in labs.

Potassium Permanganate ($KMnO_4$)

• Preparation: Prepared from Pyrolusite ore ($MnO_2$). It is fused with $KOH$ and air to form Potassium Mangante ($K_2MnO_4$), which is then oxidized (often electrolytically or in acidic medium) to Permanganate.

• Properties: Dark purple crystalline solid. Soluble in water ($6.4\,g/100\,g$ at $20^\circ C$).

• Oxidizing Nature: Acts as a strong oxidizer in acidic, neutral, and alkaline media.

  • Acidic Reaction: $MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O$

  • Example (Iodide to Iodine): $2MnO_4^- + 10I^- + 16H^+ \rightarrow 2Mn^{2+} + 5I_2 + 8H_2O$

• Uses: Used as an oxidant in organic chemistry (Baeyer's reagent), for bleaching cotton/silk, and for water purification.

Questions, Discussion, and Audience Interaction

• Greetings and Introduction: The session begins with a greeting to the "Army": "Hello my Army, what's up? Namaskar, Sat Sri Akal, Adaab, Ek Onkar, Bharat Mata ki Jai."

• Upcoming Lectures: There is an announcement for an upcoming "One Shot" session on numericals for the Solution, Electrochemistry, and Chemical Kinetics chapters starting at 12:00 PM next day.

• Instructional Dialogue: A user named "Trapper Edits" commented that reading from a PPT doesn't help students understand. The response explained that in a "One Shot" session covering 8-10 lectures in 1.5 hours, this structured format is necessary for exam preparation.

• Personal Anecdote: A story is shared about a childhood fight where the instructor beat someone so badly their face swelled up, making them look like "Angad."

• Audience Banter:

  • A student asked to meet "Bhabhi" (sister-in-law). The response was to focus on studies because "Bhabhi" won't write the exam for them.

  • A student named "Abhi Singh" declared "Keerti, I love you." The response warned "Abhi's father" that the boy is ready for marriage and distracted.

  • A student mentioned they have given up studies for everything else; they were jokingly told they are "multi-talented" and fit for jobs like washing dishes at weddings or selling momos.

• Samosa Question: Reference was made to a "two-samosa question" appearing in future classes.

• Final Notes Logistics: Students were instructed to search for the channel "Chemistry with Yo" on Telegram to find the detailed notes for the chapter.