Chemical Bonding and Molecular Structure
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What is Chemical Bonding and Molecular Structure

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Chemical bonding is the study of bonds that exist between the atoms or molecules. This chapter explains why only certain atoms combine with each other and make a new product and their arrangement in a definite shape. There are various theories such as VSEPR, valence bond theory, the molecular orbital theory that will explain all the phenomena in details. Bonding is not just an instance but it is nature's way to take every atom or molecule to its most stable state.

All the structures that exist in the universe are the result of the formation of certain kinds of bonds. This bonding in real is actually nothing but combining one atom to the other. This combination of different atoms or “bonds” occurs in several ways as follows:

(i) Ionic bond: Bond takes place after the complete exchange of electrons.

(ii) Covalent bond: Bond takes place after sharing of electrons.

(iii) Hydrogen bond: Bond takes place between a hydrogen atom and some most electronegative atoms like oxygen, nitrogen, and fluorine.

(iv) Van der Waal forces of attraction: Bond takes place by the simple attraction between the atoms.

The general structure of the chemical bond

In our body itself, all the macromolecules like DNA, RNA, proteins, etc are held together with the help of this chemical bonding. All the structures are held together with the help of this chemical bond, either the bond is stronger or weaker. Based on the strength of the bonds, the stability of the structure is determined. The melting point, boiling point, etc are the important properties that are determined by the strength of the chemical bond. This chapter is usually liked by every student as it is very easy and it holds enough distribution of marks in Board exam and other competitive exams like JEE and NEET.

Notes for Chemical Bonding and Molecular Structure

In this section, you will study about the important topics of the chapter, overview, formulae and some important tips and guidelines for the preparation of the chapter at the best.

Important Topics:

There are the following important topics that are covered in this chapter:

(i) Ionic bonding

(ii) Fazan’s rule

(iii) Coordinate bond and exceptions to the octet rule

(iv) Covalent bonding

(v) Formal charge and Lewis dot structures

(vi) Bond energy, Bond length, Bond angle and dipole moment

(vii) Valence Shell Electron Pair Repulsion (VSEPR) theory

(viii) Valence Bond Theory (VBT)

(ix) Hybridization and its types

(x) Molecular Orbital Theory (MOT)

Overview of Chemical Bonding:

All atoms in this universe seek to achieve their stable electronic configuration in the “Noble gas” configuration. Atoms except Hydrogen achieve this stable noble gas configuration by following the octet rule in the following ways:

(i) Ionic bond: In this type of bond, metals and non-metals take part in the bond formation by the complete exchange of electrons as depicted in the picture below:

Ionic bond formation

(ii) Fazan's Rule: This rule states that in every ionic bond there is always some percentage of covalent character. This covalent character depends upon the size of anion and cation, a charge of anion and cation. As the charge on cation is larger and its size is smaller than its polarising power increases and thus the covalent character increases. Similarly for anion, if its charge is higher and size is also larger then its polarisability increases and thus the covalent character increases.

Fajan's Rule

(iii) Covalent bond: This type of bond formation takes place by the sharing of electrons between the non-metals. The picture given below shows its representation.

Covalent bond formation

In this chapter, you will learn about the Lewis dot structures. Lewis dot structure is the simple representation of the molecules formed by the covalent bonds. But in this concept, a geometry of the molecules needs to be determined, which is one of the major drawbacks of this concept. So to overcome these drawbacks, several advanced theories have been given by the scientists and they are VSEPR, VBT, and MOT.

(iv) Kossel Lewis Approach: This is the simplest model for explaining the structures of the chemical bond. This approach considers the central atom as sphere and electrons as point charges around it. Now, these point charges electrons are shared between atoms or completely exchanged between atoms and form the covalent and ionic bond respectively. After the formation of these bonds, all the atoms engaged in bonding achieve the stable noble gas configuration.

a covalent bond between two Cl atoms

(v) VSEPR Theory:

In VSEPR theory, it was being said that the shapes of the molecules are determined by the combination of lone pair of electrons and bond pair electrons.
These electrons repel each other. In order to minimize the repulsion, these electrons arrange themselves at the maximum distance and hence form the geometry.
Some common geometries of the molecules are tetrahedral, square planar, octahedral, etc.

Molecule Type	Molecule Shape	Examples
AB₂	Linear	CO₂
AB₃	Trigonal Planar	BF₃
AB₄	Tetrahedral	CH₄
AB₅	Trigonal bi-pyramidal	PCl₅
AB₆	Octahedral	SF₆

(vi) Valence Bond Theory:

The bond formation takes place only by the valence orbitals containing unpaired electrons and spinning in opposite directions.
Bond formation takes place by partial overlapping of orbitals. So, according to this theory, there are some various kinds of overlapping that occurs during bond formation like s-s overlapping, s-p overlapping, p-p overlapping and pi bond (lateral overlapping of p orbital).

(vii) Hybridization:

This concept says that during the time of bond formation, first intermixing of orbitals of comparable energies occurs to produce the new orbitals, also known as hybrid orbitals and then bond formation occurs. The hybridization concept eliminates all the drawbacks that were not solved by the earlier theories.
The number of hybrid orbitals produced is equal to the number of atomic orbitals.
The hybrid orbitals are identical in shape, size, energy, etc.
The hybrid orbitals always form a sigma bond.

Molecule shape	Hybridization
Linear	sp
Trigonal Planar	sp²
Tetrahedral	sp³
Trigonal Bi-pyramidal	sp³d
Octahedral	sp³d²
Pentagonal Bi-pyramidal	sp³d³

For example, BeF₂ This bond is not explained by VSEPR and VBT, thus hybridization explains its bond formation and structure. This is explained below:

CHEMICAL BONDING AND MOLECULAR STRUCTURE
Bond formation after hybridization

Finally, at the end of this chapter, you will learn about a new theory i.e “Molecular Orbital Theory”. This theory is applicable to only diatomic molecules like O₂, N₂, F₂, etc. This theory explains several things like electron distribution in bonding and antibonding molecular orbitals, bond order, paramagnetic or diamagnetic nature of molecules.

How to prepare for Chemical bonding?

Although this chapter is a part of physical chemistry it is completely theory-based chapter. For preparing this chapter, formula or numerical practice is not required. For solving the questions of this chapter, first, you must have a complete understanding of Atomic structure and classification of elements and periodicity in properties chapters. For a good hold in this chapter, you must give a mock test after completing the theory and you need to go through class 11th NCERT book thoroughly.

Prescribed Books

For chemical bonding and molecular structure, first, you need to finish the theory thoroughly from the NCERT book and then solve the examples and questions given in the book. Apart from this, if you want to prepare for the advanced level for competitive exams like JEE and NEET, you must read the book - O.P Tandon or P. Bahadur. Meanwhile, in the preparation, you must continuously take the mock tests for internal assessment.

Chemistry Chapter- wise Notes for Engineering and Medical Exams

Chapters No.	Chapters Name
Chapter 1	Some basic concepts in chemistry
Chapter 2	States of matter
Chapter 3	Atomic Structure
Chapter 4	Solutions
Chapter 5	Chemical Thermodynamics
Chapter 6	Equilibrium
Chapter 7	Redox Reaction and Electrochemistry
Chapter 8	Chemical kinetics
Chapter 9	Surface Chemistry
Chapter 10	General Principle and processes of Isolation of metals
Chapter 11	Classification of Elements and Periodic table
Chapter 12	Hydrogen
Chapter 13	p- block Elements
Chapter 14	s-block Elements (Alkali and Alkaline Earth Metals)
Chapter 16	d- and f- BLOCK ELEMENTS
Chapter 17	Coordination Compounds
Chapter 18	Environmental Chemistry
Chapter 19	Purification and Characterisation of Organic Compounds
Chapter 20	Some Basic Principles of Organic Chemistry
Chapter 21	Hydrocarbons
Chapter 22	Organic Compounds containing Halogens
Chapter 23	Organic Compounds containing Oxygen
Chapter 24	Organic Compounds Containing Nitrogen
Chapter 25	Polymers
Chapter 26	Biomolecules
Chapter 27	Chemistry in Everyday Life
Chapter 28	Principles Related to Practical Chemistry

Topics from Chemical Bonding and Molecular Structure

Kossel - Lewis approach to chemical bond formation, concept of ionic and covalent bonds ( JEE Main ) (7 concepts)
Valence Shell Electron Pair Repulsion (VSEPR) theory and shapes of simple molecules. ( JEE Main ) (9 concepts)
Resonance ( JEE Main ) (1 concepts)
Fajans rule, dipole moment ( JEE Main ) (4 concepts)
Hydrogen bonding and its applications. ( JEE Main ) (12 concepts)
Valence bond theory - Its important features, concept of hybridization involving s, p and d orbitals ( JEE Main ) (11 concepts)
sigma and pi-bonds ( JEE Main ) (3 concepts)
MOT:Its important features, LCAOs, types of molecular orbitals (bonding, antibonding) ( JEE Main ) (13 concepts)
molecular orbital electronic configurations of homonuclear diatomic molecules ( JEE Main ) (2 concepts)
concept of bond order ( JEE Main ) (1 concepts)
Formation of ionic bonds, factors affecting the formation of ionic bonds ( JEE Main ) (1 concepts)
ELECTRONIC THEORY OF CHEMICAL BONDING ( JEE Main ) (5 concepts)
FORMATION OF IONIC OR ELECTROVALENT BOND ( JEE Main ) (2 concepts)
BOND PARAMETER ( JEE Main ) (4 concepts)
VALENCE BOND THEORY ( JEE Main ) (2 concepts)
HYBRIDISATION ( JEE Main ) (2 concepts)
THE VALENCE SHELL ELECTRON PAIR REPULSION THEORY ( JEE Main ) (2 concepts)
MOLECULAR ORBITAL THEORY ( JEE Main ) (4 concepts)
POLARITY OF BONDS ( JEE Main ) (2 concepts)
HYDROGEN BONDING ( JEE Main ) (1 concepts)
VAN DER WAAL'S FORCES ( JEE Main ) (1 concepts)
SMART TIPS: CHEMICAL BONDING AND MOLECULAR STRUCTURE ( JEE Main ) (1 concepts)