NCERT Book Class 11 Chemistry Chapter 4 Chemical Bonding and Molecular Structure

Unit 4

CHEMICAL BONDING AND
MOLECULAR STRUCTURE

Scientists are constantly discovering new compounds,
orderly arranging the facts about them, trying to explain
with the existing knowledge, organising to modify the
earlier views or evolve theories for explaining the newly
After studying this Unit, you will be observed facts.
able to
• understand Kössel-Lewis
approach to chemical bonding;

• explain the octet rule and its Matter is made up of one or different type of elements.
limitations, draw Lewis structures Under normal conditions no other element exists as an
of simple molecules; independent atom in nature, except noble gases. However,
• explain the formation of different a group of atoms is found to exist together as one species
types of bonds; having characteristic properties. Such a group of atoms
is called a molecule. Obviously there must be some force
• describe the VSEPR theory and
which holds these constituent atoms together in the
predict the geometry of simple
molecules; molecules. The attractive force which holds various
constituents (atoms, ions, etc.) together in different
• explain the valence bond chemical species is called a chemical bond. Since the
approach for the formation of
formation of chemical compounds takes place as a result of
covalent bonds;
combination of atoms of various elements in different ways,
• predict the directional properties it raises many questions. Why do atoms combine? Why are
of covalent bonds; only certain combinations possible? Why do some atoms
• explain the different types of
combine while certain others do not? Why do molecules
hybridisation involving s, p and possess definite shapes? To answer such questions different
d orbitals and draw shapes of theories and concepts have been put forward from time
simple covalent molecules; to time. These are Kössel-Lewis approach, Valence Shell
Electron Pair Repulsion (VSEPR) Theory, Valence Bond (VB)
• describe the molecular orbital
theory of homonuclear diatomic Theory and Molecular Orbital (MO) Theory. The evolution
molecules; of various theories of valence and the interpretation of
the nature of chemical bonds have closely been related to
• explain the concept of hydrogen
the developments in the understanding of the structure
bond.
of atom, the electronic configuration of elements and the
periodic table. Every system tends to be more stable and
bonding is nature’s way of lowering the energy of the system
to attain stability.

Unit 4.indd 100 9/12/2022 9:36:09 AM