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So! Chemistry just got serious - and it’s jumping into The d- and f-Block Elements. Sounds like oxidation chaos at first, but honestly? Once you spot the trends, it’s actually super scoring and not that scary. Whether it’s colored ions, configurations, lanthanoid contraction, or classic KMnO₄ reactions – we’ve got you sorted.
These all the d and f block elements class 12 notes have it all: NCERT facts, easy definitions, key reactions, and quick ways to tackle tricky concepts without confusion. Clean, clear, and exam-focused.
The d and f block Elements Class 12 Notes
So if you're stuck switching tabs, scribbling oxidation states, or just dreading another f-block question – stop right here. These the d and f block elements notes class 12 are made to simplify things fast. From electronic configs to properties and board-fav reactions, this is your all-in-one guide. No fluff, just what matters.
What Are d- and f-Block Elements? – Explained with Examples
These are metallic elements where the last electron enters a d - or f - orbital. They lie in the center and bottom part of the periodic table and are known for forming colored ions, showing variable oxidation states, and acting as catalysts. Based on their orbital filling, they’re divided into two main blocks:
1. d-Block Elements (Transition Elements)
These are found in Groups 3 to 12, where the last electron enters a (n−1) d orbital. They act as a bridge between s- and p-block elements and show a wide range of physical and chemical properties.
Features:
- Found in the center of the periodic table
- Show variable oxidation states
- Form colored ions and complex compounds
- Often used as catalysts
- General configuration: (n−1)d¹⁻¹⁰ ns¹⁻²
Examples: Iron (Fe), Copper (Cu), Zinc (Zn), Chromium (Cr)
2. f-Block Elements (Inner Transition Elements)
These are placed in two rows at the bottom of the periodic table. The last electron enters an (n−2)f orbital. They include lanthanoids and actinides and are known for radioactive behavior and lanthanide contraction.
Features:
- Found in the bottom two rows
- Include lanthanoids and actinoids
- Show lanthanide contraction
- Mostly radioactive (actinoids)
- General configuration: (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns²
Examples: Cerium (Ce), Neodymium (Nd), Uranium (U), Thorium (Th)
Electronic Configuration – the d and f block elements notes class 12 Format
The electronic configuration of these elements tells us where the last few electrons are going - and that explains most of their behavior. Whether it’s color, oxidation states, or magnetic properties, it all starts with how their orbitals are filled.
1. d-Block Elements
The last electron goes into the (n−1)d orbital. But their outermost electrons are still in the ns orbital, so both can affect reactions.
General Configuration: (n−1)d¹⁻¹⁰ ns¹⁻²
What to Remember:
- The 3d, 4d, and 5d series are the ones you need to focus on
- Sometimes 4s fills before 3d, but 3d gets written later (like in Fe, Cu etc.)
- Some elements like Cr and Cu show “extra stable” configurations (half-filled or full d orbitals)
Examples:
- Cr = [Ar] 3d⁵ 4s¹ (half-filled d)
- Cu = [Ar] 3d¹⁰ 4s¹ (full d)
- Fe = [Ar] 3d⁶ 4s²
2. f-Block Elements
These elements fill their electrons in the (n−2)f orbital, which lies even deeper inside the atom.
General Configuration: (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns²
What to Remember:
- Lanthanoids fill the 4f orbital (from Ce to Lu)
- Actinoids fill the 5f orbital (from Th to Lr)
- Many of them are radioactive and form complex ions
Examples:
- Ce = [Xe] 4f¹ 5d¹ 6s²
- U = [Rn] 5f³ 6d¹ 7s²
Periodic Trends & Properties – the d and f block elements notes Style
Just like s- and p-blocks, d- and f-block elements also follow periodic trends - but with their own unique twist. These trends explain why they behave the way they do in reactions.
1. Trends in d-Block Elements
These elements show typical metallic properties, but also some special ones that make them stand out.
Key Properties & Trends:
- Variable oxidation states (like Fe²⁺ and Fe³⁺)
- Colored compounds (due to unpaired d-electrons)
- Magnetic properties (paramagnetism if unpaired e⁻ are present)
- Catalytic behavior (like Fe, Ni in industrial reactions)
- High melting and boiling points
- Form complex compounds easily
Trend Tip: As you move left to right in a d-block period, nuclear charge increases → atomic size slightly decreases → properties gradually change.
2. Trends in f-Block Elements
f-block elements are a bit more complex, but you only need to focus on the basics for boards.
Key Properties & Trends:
- Show a steady decrease in atomic and ionic size → called lanthanoid contraction
- Have variable oxidation states, but +3 is the most common
- Poor shielding by f-electrons → affects bonding and size
- Many actinides are radioactive
- Usually form complex ions with ligands
Trend Tip: f-orbitals are buried deep, so the changes are subtle — but the lanthanoid contraction affects the size and chemistry of elements that come after them too (like Hf vs Zr).
Lanthanides Contraction – Core Concept in ch 8 chemistry class 12 notes pdf
Lanthanide contraction sounds fancy, but it’s actually one of the easiest concepts in this chapter. It’s all about how atomic size slowly decreases across the lanthanide series - and that small shrinkage causes big effects later in the periodic table.
What is Lanthanide Contraction?
As we move across the lanthanoid series (from Ce to Lu), the atomic and ionic sizes gradually decrease. This happens because the electrons are added to the 4f orbitals, which have poor shielding. The nucleus pulls the electrons in tighter, making the atoms slightly smaller step-by-step.
Effects of Lanthanide Contraction
- Zr and Hf have almost the same size despite being in different periods
- Affects the basic strength of hydroxides (decreases across the series)
- Makes it harder to separate lanthanoids due to similar properties
- Impacts the chemical behavior of later d-block elements
d-Block vs f-Block – Full Comparison Table
With so many properties floating around, it’s easy to get confused between d-block and f-block elements. Here's a neat side-by-side comparison to help you lock it down once and for all.
KMnO₄ and K₂Cr₂O₇ – Important Reactions and Uses
This part of the chapter is a direct question zone in most board papers. Both these compounds are strong oxidising agents - and remembering 2–3 key reactions can easily earn you full marks. Let’s break them down one by one.
1. Potassium Permanganate (KMnO₄)
KMnO₄ is a deep purple crystal used in redox titrations. It acts as a strong oxidising agent in acidic, neutral, and basic media - but acidic is the one most often asked in exams.
Oxidising Action (Acidic Medium):
Mn in KMnO₄ goes from +7 to +2
Balanced Reaction:
2KMnO4+3H2SO4→K2SO4+2MnSO4+3H2O+5[O]2 KMnO₄ + 3 H₂SO₄ → K₂SO₄ + 2 MnSO₄ + 3 H₂O + 5 [O]2KMnO4+3H2SO4→K2SO4+2MnSO4+3H2O+5[O]
Key Uses:
- Converts Fe²⁺ → Fe³⁺
- Oxidises oxalic acid → CO₂
- Common in redox titrations
- Also used in disinfecting water
2. Potassium Dichromate (K₂Cr₂O₇)
K₂Cr₂O₇ is orange-red in color and works similarly - but with chromium instead of manganese.
Oxidising Action (Acidic Medium):
Cr goes from +6 to +3
Balanced Reaction:
K2Cr2O7+4H2SO4+3SO2→Cr2(SO4)3+K2SO4+4H2OK₂Cr₂O₇ + 4 H₂SO₄ + 3 SO₂ → Cr₂(SO₄)₃ + K₂SO₄ + 4 H₂OK2Cr2O7+4H2SO4+3SO2→Cr2(SO4)3+K2SO4+4H2O
Key Uses:
- Oxidises iodide to iodine
- Converts SO₂ to H₂SO₄
- Used in dyeing, leather tanning, and lab prep work
Conclusion
And that’s a wrap on the d and f block elements class 12 notes - from trends to reactions, electronic configs to color changes, you’ve got the full chapter sorted now. Remember, this one’s all about smart patterns and selective memorisation.
Keep revising those exceptions (like Cr, Cu, lanthanide contraction), and you’ll walk into the exam confident.and also don’t skip the reactions of KMnO₄ and K₂Cr₂O₇ - they’re simple but super common in board questions.
FAQs
Q1. What are d- and f-block elements?
Ans. d-block elements have their last electron in the (n−1)d orbital, and f-block elements fill the (n−2)f orbital. They're found in the middle and bottom of the periodic table.
Q2. Why are d-block elements coloured?
Ans. Their compounds are coloured because of d-d transitions, where electrons absorb light and jump between energy levels in the d-orbitals.
Q3. What is lanthanide contraction?
Ans. It’s the gradual decrease in atomic size across the lanthanide series due to poor shielding by 4f electrons, affecting elements after them too.
Q4. Why do d-block elements show variable oxidation states?
Ans. Because they have electrons in both d and s orbitals, they can lose different numbers of electrons in reactions.
Q5. What are KMnO₄ and K₂Cr₂O₇ used for?
Ans. They’re strong oxidising agents used in redox titrations, water treatment, and organic chemistry reactions.
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