Class 11 Exam  >  Class 11 Notes  >  Detailed Chapter Notes - Chemical Bonding & Molecular Structure, Class 11, Chemistry

Chemical Bonding & Molecular Structure, Class 11, Chemistry Detailed Chapter Notes PDF Download

Types of Bonds - Chemical Bonding & Molecular Structure, Class 11, Chemistry

KEY CONCEPTS

INTRODUCTION

A molecule will be formed if it is more stable and has a lower energy than the individual atom. Normally only electrons in the outermost shell of an atom are involved in forming bonds, and in this process each atom attains a stable electronic configuration of an inert gas.

Types of Bonds :

Atoms involved                                                                       Bonding

(I) Metal + Nonmetal                                                                        Ionic

(II) Nonmetal + Nonmetal                                                                 Covalent

(III) Metal + Metal                                                                           Metallic

(IV) Electron deficient molecule or ion (Lewis acid) and                     Coordinate 

electron rich molecule or ion (Lewis base)

(V) H and electronegative elements (N, O, F some times with Cl)      Hydrogen

Ionic, Covalent and coordinate bonding

Ionic bonding

An ionic bond is formed when a metal atom transfers one or more electrons to a non-metal atom.

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

The oppositely charged ions get attracted through electrostatic force of attraction.

Properties of ionic compounds 

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure In the solid state, each cation surrounds itself with anions and each anion with cations. These very large number of ions are arranged in an ordinary network called ionic crystals.

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure They are good conductors of electricity in fused state or aqueous solution.

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure They are generally soluble in polar solvents and insoluble in non-polar solvents.

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure Have high melting point and boiling point than covalent compounds.

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure Have strong force of attraction between cation and anion (Coulombic force)

F = CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

Where Z1 and Z2 are charge on the ions, D is dielectric constant of the medium and r the inner-ionic distance (i.e., bond length).

Born-Haber cycle It is an indirect method to calculate the lattice energy of an ionic compound. For example, the lattice energy of sodium chloride can be calculated as follows.
 

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

Now, according to Hess's law,

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure = S IE1  D/2 - EA1 - U

Where S is the enthalpy of sublimation of metal (Na), IE1 is the first ionisation energy of sodium, D is the bond dissociation energy of Cl1 molecule, EA1 is the first electron affinity of Cl, U is the lattice energy of NaCl(s) and DHformation is the enthalpy of formation of NaCl.

Covalent Bonding :

Whenever Chemical bond is formed by sharing of electrons then it is named as covalent bond.

Coordinate Bonding or Dative Bond :

Whenever covalent bond is formed by unequal sharing of a pair of electrons between a Lewis base and Lewis acid is called coordinate bond.

(I) It is represented as (→) and considered as σ bond.

(II) Atom/ion/molecule donating electron pair is called donor or Lewis base.

(III) Atom/ion/molecule accepting electron pair is called acceptor or Lewis acid.

Formation of NH4  :

NH3 has three (N - H) bonds and one lone pair. In NH4  formation. This lone pair is donated to H  ion.

: NH3 + H+ → NH4

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

Note : In a multiple bond (CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure) sign is treated as a pi-covalent bond (Bock bond).

===================================================================

Valence Bond Theory - Chemical Bonding and Molecular Structure, Class 11, Chemistry

Valence Bond (V.B) theory :

According to this theory, a covalent bond is formed by the overlapping of atomic orbitals. Important points of this theory are summarised below.

(I) Orbitals undergoing overlapping should be half-filled.

(II) Half-filled orbitals should contain the electron with opposite spin.

(III) Strength of a covalent bond depends upon the extent of overlapping, for example, axial or lateral overlapping.

(IV) If the atomic orbitals overlap axially, then the bond formed is called a sigma (s) bond.

(V) A sigma bond is always stronger than a pi-bond.

(VI) Covalent bonds formed by the overlap of s-s and s-p orbitals are always sigma.

(VII) By the overlap of p-p orbitals, one sigma and two pi bonds are formed.

(VIII) Increasing strength of s covalent bonds is in the order s - s < s - p < p — p (when internuclear distance is constant)

(IX) A single covalent bond is always a sigma bond. In a double covalent bond, one is sigma and the other is pi-bond. In a triple covalent bond, one is sigma and two are pi-bonds.

Hybridisation :

It is defined as the concept of intermixing of orbitals of same energy or of slightly different energy to produce entirely new orbitals of equivalent energy, identical shapes and which are symmetrically disposed is plane.

Important features of hybridisation are given below.

(I) Only the orbitals generated are equal in number to that of pure atomic orbitals which are intermixed.

(II) The hybrid orbitals generated are equal in number to that of pure atomic orbitals which are intermixed.

(III) A hybrid orbital, like an atomic orbital, can have two electrons of opposite spins.

(IV) Hybrid orbitals usually form sigma bonds. If there are pi-bonds, equal number of atomic orbitals must be left unhybridised for pi-bonding.

Valence shell electron pair repulsion (VSEPR) Theory (Gillespie theory) :

(I) The shape of a molecule is determined by repulsion between the electron pairs (lp and bp) present in the valence shell of the central atom.

(II) The order of repulsion is (lp-lp) > (lp-bp) > (bp-bp)

Determination of the Type of Hybridisation :

The number of electron pairs = Bond Pairs lone pairs

(s Bond)

Table Shapes of molecules on the basis of VSEPR theory and hybridisation

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

===============================================================

Molecular Orbital Theory - Chemical Bonding and Molecular Structure, Class 11, Chemistry

Molecular Orbitals (M.O.) Theory :

(I) There is Linear combination of Atomic Orbitals (LCAO) to form molecular orbitals (M.O.)

(II) The number of molecular orbitals produced is equal to the number of atomic orbitals that are combined.

(III) Two types of molecular orbitals are formed.

(a) Bonding molecular orbitals at a lower energy than the combining atomic orbitals which favour bond formation.

(b) Anti - bonding molecular orbitals at a higher energy than the combining atomic orbitals which opposes the bond formation.

Following molecular orbitals are formed when atomic orbitals overlap.

Atomic orbitals                  Bonding M. O.                Anti-bonding M.O.

1s + 1s                              σ1s                                         σ* 1s

2s + 2s                             σ2s                                          σ* 2s

2px + 2px                                     σ 2px                                        σ* 2px

2py + 2py                          π 2py                                        π* 2py

2pz + 2pz                         π 2pz                                          π* 2pz

Electrons are filled in the increasing order of energy of the molecular orbitals which is in order of Aufbau rule

(a) When total electrons in the molecule or ions are more than 14(simple order of energy level of M. O.).

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

(b) When total number of electrons in the molecule are ions are £14 (modified order of energy level of M.O.).

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

(I) The electrons are filled in molecular orbitals in the same way as in atomic orbitals, that is, as per the Hund's Rule, Pauli exclusion principle and Aufbau rule.

(II) Number of covalent bonds between two atoms is called Bond order and is given by

Bond order (B.O.) = CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

Where, NB = number of electrons in bonding molecular orbital and NA = number of electrons in anti bonding molecular orbitals.

(III) For a stable molecule/ion, NB > NA

(IV) A given molecule or ion is paramagnetic if it has unpaired electrons in the molecular orbital. Otherwise it is diamagnetic

(V) Greater the bond order, shorter the bond length and greater the bond energy. Thus for O2, O2  , O2,O22-
 

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

 

Fajan's Rule :

This rule is used to decide relative ionic & covalent character in a molecule. A molecule is predominantly covalent if

(I) Smaller the size of cation.

(II) larger the size of anion.

(III) greater the charge on cation and anion.

(IV) ion does not have inert gas configuration but it possesses pseudo inert gas configuration (18 electrons in the ultimate shell).

(I) CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

(II) CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

(III) CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

(IV) CuCl and NaCl

[Cu ] = [Ar]3d10 ; [Ne ] = [Ne]

Cations with 18-electron shells (pseudo inert gas configuration) has grater polarising power than 8-electron shell (inert gas configuration) ion with the same charge and size. Thus, CuCl is more covalent than NaCl.

 

Hydrogen Bonding :

(I) The concept of H-bonding was introduced by Latimer and Rodebush.

(II) H-bonding is said to be formed when slightly acidic hydrogen attached to a strongly electronegative atom such as F, O and N is held with weak electrostatic forces by the non- bonded pair of electron of another atom. That is , it is a dipole-dipole interaction.

(III) Of all the electronegative donor atoms, only F, O. and N enter into stable H-bond formation.

(IV) The weak electrostatic interaction leading to the H-bond formation is shown by dashed(.....) lines.

(V) Greater the electronegativity difference, stronger is the H-bond. For example,

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

 

Intramolecular H-bonding ;

This type of H-bonding occurs when polar H and electronegative atom are present in the same molecule.

(a) o-hydroxy benzaldehyde                     (b) o-nitrophenol

CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure                           CBSE, Class 11, IIT JEE, Syllabus, Preparation, AIPMT, NCERT, Important, Chemical Bonding, Molecular Structure

Intermolecular H-bonding

This type of H-bonding takes place between hydrogen and electronegative element (like F,O,N) present between molecules of the same substance (H2O and H2O) or different substances (H2O and NH3).

The document Chemical Bonding & Molecular Structure, Class 11, Chemistry Detailed Chapter Notes is a part of Class 11 category.
All you need of Class 11 at this link: Class 11

Top Courses for Class 11

FAQs on Chemical Bonding & Molecular Structure, Class 11, Chemistry Detailed Chapter Notes

1. What is chemical bonding?
Ans. Chemical bonding is a process that involves the formation of new substances by combining two or more atoms, ions, or molecules. It is the force of attraction between the atoms or molecules that holds them together in a specific arrangement. In chemical bonding, the electrons of the atoms are involved, and they are either shared or transferred between the atoms to form a stable compound.
2. What are the types of chemical bonds?
Ans. There are three types of chemical bonds: (i) Ionic Bond: It is formed between two atoms that have a large difference in their electronegativity. In ionic bonding, one atom donates an electron to another atom. This results in the formation of positively charged cations and negatively charged anions. (ii) Covalent Bond: It is formed when two atoms share electrons to complete their outermost shell. This type of bond is formed between non-metals, and the shared electrons are attracted to the positively charged nuclei of both the atoms. (iii) Metallic Bond: It is formed between metal atoms, where the valence electrons are shared by all the atoms in the metal lattice. This type of bond results in the formation of a sea of electrons that can move freely throughout the metal.
3. What is the VSEPR theory?
Ans. The VSEPR (Valence Shell Electron Pair Repulsion) theory is used to predict the shape of molecules based on the number of electron pairs around the central atom. According to this theory, the electron pairs in the valence shell of the central atom repel each other and try to stay as far apart as possible to minimize the repulsion. The shape of the molecule depends on the number of electron pairs around the central atom, which can be bonding or non-bonding electron pairs.
4. What is hybridization?
Ans. Hybridization is the process of mixing atomic orbitals of similar energies on the same atom to form hybrid orbitals that are used in bonding. The hybrid orbitals have different shapes and energies than the original atomic orbitals, which allow for better bonding. Hybridization is used to explain the bonding in molecules and the shapes of molecules.
5. What is the difference between polar and nonpolar molecules?
Ans. Polar molecules have a permanent dipole moment due to the unequal sharing of electrons between the two atoms that form the bond. This results in a partial positive and partial negative charge on the atoms, which creates a dipole moment. Nonpolar molecules have no dipole moment because the electrons are shared equally between the atoms. The electronegativity difference between the atoms in a molecule determines whether it is polar or nonpolar.
Download as PDF
Explore Courses for Class 11 exam

Top Courses for Class 11

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Chemical Bonding & Molecular Structure

,

video lectures

,

Class 11

,

Class 11

,

past year papers

,

Chemistry Detailed Chapter Notes

,

Chemistry Detailed Chapter Notes

,

Viva Questions

,

Important questions

,

Sample Paper

,

practice quizzes

,

mock tests for examination

,

Exam

,

Extra Questions

,

MCQs

,

Objective type Questions

,

Semester Notes

,

Chemical Bonding & Molecular Structure

,

Summary

,

Previous Year Questions with Solutions

,

study material

,

shortcuts and tricks

,

Class 11

,

Chemistry Detailed Chapter Notes

,

ppt

,

Free

,

Chemical Bonding & Molecular Structure

,

pdf

;