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CBSE • कक्षा XI • Chemistry • अध्याय 4
अनुमानित समय: 45 Mins
प्रगति: अध्ययनरत

रासायनिक आबंधन तथा आण्विक संरचना

In Class 11 Chemistry, "Chemical Bonding and Molecular Structure" provides an authoritative, curriculum-verified master resource aligned with the 2026–27 NCERT syllabus.

अध्याय CBT ऑनलाइन टेस्ट दें सभी अध्याय देखें
प्रस्तावना अध्याय अवधारणाएँ अध्याय सारांश स्व-मूल्यांकन अभ्यास टेस्ट दें

⚛️ Have You Ever Wondered?

Why do two lethal chemicals—toxic sodium metal and poisonous chlorine gas—combine into harmless, delicious table salt that keeps human hearts beating? Chemical bonding is the electrostatic glue of the molecular universe.

यह अध्याय क्यों महत्वपूर्ण है

In Class 11 Chemistry, "Chemical Bonding and Molecular Structure" provides an authoritative, curriculum-verified master resource aligned with the 2026–27 NCERT syllabus.

अध्ययन से पूर्व (आवश्यक ज्ञान)

  • Valence electrons and Lewis dot symbols.
  • Periodic trends from Chapter 3.
  • Electronegativity.

इस अध्याय के लक्ष्य

  • Explain Kossel-Lewis approach and Octet Rule; identify octet limitations (incomplete, expanded octet).
  • Predict 3D molecular geometry using VSEPR Theory (linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral).
  • Analyze Valence Bond Theory (VBT): Orbital overlap ($\sigma$ and $\pi$ bonds) and Hybridization ($sp, sp^2, sp^3, sp^3d, sp^3d^2$).
  • Apply Molecular Orbital Theory (MOT): Bonding and Antibonding MOs, Bond Order ($BO = \frac{N_b - N_a}{2}$), and magnetic behavior of $O_2$ and $N_2$.
  • Explain Hydrogen Bonding (intermolecular vs intramolecular) and anomalous water boiling points.

अध्याय रूपरेखा एवं प्रगति

1 1. VSEPR Theory & Molecular Geometr...
2 2. Hybridization: Mixing Atomic Orb...
3 3. Molecular Orbital Theory (MOT)

सम्पूर्ण सैद्धांतिक एवं वैचारिक अध्ययन

1. VSEPR Theory & Molecular Geometry

Valence Shell Electron Pair Repulsion (VSEPR) predicts that electron pairs around a central atom arrange to minimize mutual electrostatic repulsion:
• Repulsion Hierarchy: $\mathbf{\text{Lone Pair-Lone Pair} > \text{Lone Pair-Bond Pair} > \text{Bond Pair-Bond Pair}}$.
• $\text{CH}_4$: 4 BP, 0 LP → Regular Tetrahedral ($109.5^\circ$).
• $\text{NH}_3$: 3 BP, 1 LP → Trigonal Pyramidal ($107^\circ$).
• $\text{H}_2\text{O}$: 2 BP, 2 LP → Bent / V-shaped ($104.5^\circ$!).

2. Hybridization: Mixing Atomic Orbitals

Hybridization is the quantum concept of intermixing atomic orbitals of slightly different energies to produce equivalent hybrid orbitals:
• sp ($180^\circ$): $\text{BeCl}_2, \text{C}_2\text{H}_2$ (Linear).
• $sp^2$ ($120^\circ$): $\text{BF}_3, \text{C}_2\text{H}_4$ (Trigonal Planar).
• $sp^3$ ($109.5^\circ$): $\text{CH}_4, \text{NH}_3, \text{H}_2\text{O}$ (Tetrahedral).
• $\sigma$ bond (head-on overlap) is stronger than $\pi$ bond (lateral sideway overlap).

3. Molecular Orbital Theory (MOT)

Linear Combination of Atomic Orbitals (LCAO) produces:
• Bonding MO ($\sigma, \pi$, lower energy, stable).
• Antibonding MO ($\sigma^*, \pi^*$, higher energy).
• Bond Order ($BO$): $$\mathbf{BO = \frac{N_b - N_a}{2}}$$ If $BO > 0$, molecule is stable; if $BO = 0$, molecule cannot exist (e.g. $\text{He}_2$). Paramagnetism of $O_2$: MOT explains why liquid $O_2$ is attracted to magnets by proving it possesses two unpaired electrons in $\pi^* 2p_x$ and $\pi^* 2p_y$!

Chemical Bonding and Molecular Structure - Key Conceptual Architecture & Molecular Model

Chemical Bonding and Molecular Structure - Molecular Architecture Thermodynamic & Kinetic Foundations Equilibrium laws & state transformations Orbital & Electronic Mechanisms VSEPR, hybridization & MOT electron density Industrial Synthesis & Competitive Analysis CBSE board problem frameworks, JEE/NEET diagnostic applications & lab benchmarks

अध्याय का सार संक्षेप एवं 10 मुख्य निष्कर्ष

मुख्य बिंदु 1
VSEPR Repulsion: LP-LP > LP-BP > BP-BP dictating bent and pyramidal shapes.
मुख्य बिंदु 2
Hybridization: Mathematical redistribution of orbital density optimizing bonding geometry.
मुख्य बिंदु 3
Sigma vs Pi: Stiff cylindrical head-on axial overlap vs flexible lateral sideway p-orbital overlap.
मुख्य बिंदु 4
Molecular Orbital Bond Order: $BO = (N_b - N_a)/2$ measuring bond multiplicity and dissociation strength.
मुख्य बिंदु 5
Oxygen Paramagnetism: MOT's definitive victory over Lewis structures by predicting unpaired $\pi^*$ electrons.

स्व-मूल्यांकन अभ्यास (Check Your Understanding)

मूल वैचारिक स्पष्टता की जांच के लिए नैदानिक प्रश्न। पहले स्वयं हल करें, फिर उत्तर देखें।

1
Why is the bond angle in water ($\text{H}_2\text{O}$) $104.5^\circ$ rather than the tetrahedral angle of $109.5^\circ$?
उत्तर एवं व्याख्या देखें
उत्तर: Oxygen in water has $sp^3$ hybridization with 2 bond pairs and 2 lone pairs. According to VSEPR theory, lone pair-lone pair repulsion is stronger than bond pair-bond pair repulsion, squeezing the $H-O-H$ bond angle down from $109.5^\circ$ to $104.5^\circ$.
Strong LP-LP repulsion compresses tetrahedral angle.
2
Calculate the bond order of $N_2$ and $O_2$ using Molecular Orbital Theory.
उत्तर एवं व्याख्या देखें
उत्तर: For $N_2$ (14 electrons): $BO = \frac{10 - 4}{2} = 3$ (stable triple bond, diamagnetic). For $O_2$ (16 electrons): $BO = \frac{10 - 6}{2} = 2$ (stable double bond, paramagnetic due to 2 unpaired electrons in $\pi^*2p$).
N2 has BO = 3; O2 has BO = 2 (paramagnetic).
3
Differentiate between a Sigma ($\sigma$) bond and a Pi ($\pi$) bond.
उत्तर एवं व्याख्या देखें
उत्तर: A $\sigma$ bond is formed by end-to-end (head-on) axial overlap of atomic orbitals along the internuclear axis (stronger, allows free rotation); a $\pi$ bond is formed by lateral (sideway) parallel overlap of $p$-orbitals (weaker, prevents rotation).
Head-on axial overlap (strong) vs sideway lateral overlap (weak).
4
Explain why $\text{PCl}_5$ has two different bond lengths (axial vs equatorial).
उत्तर एवं व्याख्या देखें
उत्तर: In trigonal bipyramidal $\text{PCl}_5$ ($sp^3d$), the two axial $P-Cl$ bonds experience greater electrostatic repulsion from the three equatorial bonds, causing axial bonds ($240\text{ pm}$) to be significantly longer and weaker than equatorial bonds ($202\text{ pm}$).
Axial bonds experience more repulsion, making them longer.
5
What is Hydrogen Bonding? Distinguish between Intermolecular and Intramolecular H-bonding.
उत्तर एवं व्याख्या देखें
उत्तर: Hydrogen bonding is an electrostatic dipole attraction between a hydrogen atom bonded to a highly electronegative atom ($F, O, N$) and another electronegative atom. Intermolecular occurs between separate molecules (e.g. $\text{H}_2\text{O}$, elevating boiling point); Intramolecular occurs within the same molecule (e.g. o-nitrophenol).
Electrostatic attraction involving H bonded to F, O, N.
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फाउंडेशन टेस्ट
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15 MCQs • HOTS और ट्रैप्स

कक्षा 11 Chemistry के सभी अध्याय

अध्याय 1: रसायन विज्ञान की कुछ मूल अवधारणाएं अध्याय 2: परमाणु की संरचना अध्याय 3: तत्वों का वर्गीकरण एवं गुणधर्मों में आवर्तिता अध्याय 4: रासायनिक आबंधन तथा आण्विक संरचना अध्याय 5: ऊष्मागतिकी (Thermodynamics) अध्याय 6: साम्यावस्था (Equilibrium) अध्याय 7: अपचयोपचय अभिक्रियाएं (Redox Reactions) अध्याय 8: कार्बनिक रसायन - कुछ आधारभूत सिद्धांत तथा तकनीकें अध्याय 9: हाइड्रोकार्बन (Hydrocarbons)

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