Chemical Bonding and Molecular Structure - Notes, Topics, Books, FAQs

“What You Lack In Talent Can Be Made Up With Desire, Hustle And Giving 110% All The Time.” – Don Zimmer

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.

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:

(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.

(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.

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.

(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.

(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.

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

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.