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,CHEMICAL
BONDING
, MARKS 3
1. INTRODUCTION
A chemical bond is the physical process responsible for the attractive interactions between atoms
and molecules, and that which confers stability to diatomic and polyatomic chemical compounds.
In general, strong chemical bonding is associated with the sharing or transfer of electrons between
the participating atoms. Molecules, crystals and diatomic gasesăindeed most of the physical
environment around usăare held together by chemical bonds, which dictate the structure of
matter.
Bonds vary widely in their strength which is associated both with the energy required to break
them, and the forces they exert on the atoms they hold together. Generally covalent and ionic
bonds are often described as „strong‰, whereas hydrogen bonds and van der Waal’s bonds are
generally considered to be „weak,‰ although there exist overlaps in strength within these bond
classes.
Since opposite charges attract via a basic electromagnetic force, the negatively-charged orbiting
the nucleus and the positively-charged protons in the nucleus attract each other. Also, an electron
positioned between two nuclei will be attracted to both of them. Thus, the most stable configuration
of nuclei and electrons is one in which the electrons spend more time between nuclei, than
anywhere else in space. These electrons cause the nuclei to be attracted to each other. However,
this assembly cannot collapse to a size dictated by the volumes of these individual particles. Due
to the matter wave nature of electrons and their relatively smaller mass, they occupy a very much
larger amount of volume compared with the nuclei, and this volume occupied by the electrons
keeps the atomic nuclei relatively far apart, as compared with the size of the nuclei themselves.
1 . 1 Cause of C hemical C omb ination
The atoms interact with each other on account of the following reasons :
(i) Decrease in energy : It is a fundamental truth that all natural systems tend to lose
potential energy and become more stable. Other things being equal, a system that has stored
potential energy is less stable than a system that has none. It is an observed fact that a
bonded state is more stable than unbonded stable. This is due to the fact that the bonded
state has lower potential energy than unbonded state. Hence, when two atoms approach
each other, they combine only under the condition that there is a decrease in potential
energy.
When two atoms approach each other, new forces of attraction and repulsion come into play.
The forces of attraction are between the nucleus of one atom and the electrons of the other.
The forces of repulsion are between two nuclei as well as between the electrons of the two
atoms. If the net result is attraction, the total potential energy of the system decreases and
a chemical bond results. No chemical bonding is possible if net result is repulsion.
(ii) Lewis octet rule : The noble gases are known for their lack of chemical activity. There are
no known compounds of helium, neon and argon. Why are these elements so unreactive
CHEMICAL BONDING
, 4 MARKS
towards other elements ? All these elements have electronic structures that consist of filled
outermost sheels. Except for helium, whose electronic configuration is 1s2, the s-and p-
subshells of the highest energy level contain a total of eight electrons. It is, therefore,
concluded that s2p6 configuration in the outer energy level constitutes a-structure of maximum
stability and therefore, of minimum energy.
The atoms of all elements when enter into chemical combination try to attain noble gas
configuration, i.e., they try to attain either 2 electrons (when only one energy shell) or 8
electrons in their outermost energy level which is of maximum stability and hence of minimum
energy. The tendency of atoms to achieve eight electrons in their outermost shell is known
as Lewis octet rule. Octet rule was the basis of electronic theory of valency.
1 . 2 L ewis Symb ols of E lement s
Chemical bonding mainly depends on the number of electrons present in the outermost energy
level. These electrons are termed as valency electrons. The electronic configuration of sodium (Na)
is 2, 8, 1 and that of sulphur has (S) 2, 8, 6. Thus, sodium has one valency electron while sulphur
has six valency electrons.
The valency electrons in atoms are shown in terms of Lewis symbols. To write Lewis symbol for
an element, we write down its symbol surrounded by a number of dots of crosses equal to the
number of valency electrons. Paired and unpaired valency electrons are also indicated. The Lewis
symbols for hydrogen, sodium, nitrogen, oxygen and chlorine may be written as :
H Na N O Cl
Generalised, Lewis symbols for the representative elements are given in the following table :
1 2 13 14 15 16 17
Group IA IIA IIIA IVA VA VIA VIIA
Lewis symbol X X X X X X X
1 . 3 E lect r onic t heor y of Valency
The theory of valency explains chemical combination in terms of electrons. The theory was
developed independently by W. Kossel and G.N. Lewis (1916) and extended by Irving Langmuir
(in 1919).
The chemical behaviour of an atom is determined to a large extent by the number and arrangement
of electrons in the outer orbitals of the atom. Only these electrons are involved in chemical
combination and so these are called the valence electrons.
CHEMICAL BONDING
JEE Main JEE Adv. BITSAT WBJEE MHT CET and more...
4.8 50,000+ 2,00,000+
Rating on Google Play Students using daily Questions available
With MARKS app you can do all these things for free
Solve Chapter-wise PYQ of JEE Main, JEE Advanced, NEET, BITSAT, WBJEE, MHT CET & more
Create Unlimited Custom Tests for any exam
Attempt Top Questions for JEE Main which can boost your rank
Track your exam preparation with Preparation Trackers
Complete daily goals, rank up on the leaderboard & compete with other aspirants
4.8 50,000+ 2,00,000+
Rating on Google Play Students using daily Questions available
,CHEMICAL
BONDING
, MARKS 3
1. INTRODUCTION
A chemical bond is the physical process responsible for the attractive interactions between atoms
and molecules, and that which confers stability to diatomic and polyatomic chemical compounds.
In general, strong chemical bonding is associated with the sharing or transfer of electrons between
the participating atoms. Molecules, crystals and diatomic gasesăindeed most of the physical
environment around usăare held together by chemical bonds, which dictate the structure of
matter.
Bonds vary widely in their strength which is associated both with the energy required to break
them, and the forces they exert on the atoms they hold together. Generally covalent and ionic
bonds are often described as „strong‰, whereas hydrogen bonds and van der Waal’s bonds are
generally considered to be „weak,‰ although there exist overlaps in strength within these bond
classes.
Since opposite charges attract via a basic electromagnetic force, the negatively-charged orbiting
the nucleus and the positively-charged protons in the nucleus attract each other. Also, an electron
positioned between two nuclei will be attracted to both of them. Thus, the most stable configuration
of nuclei and electrons is one in which the electrons spend more time between nuclei, than
anywhere else in space. These electrons cause the nuclei to be attracted to each other. However,
this assembly cannot collapse to a size dictated by the volumes of these individual particles. Due
to the matter wave nature of electrons and their relatively smaller mass, they occupy a very much
larger amount of volume compared with the nuclei, and this volume occupied by the electrons
keeps the atomic nuclei relatively far apart, as compared with the size of the nuclei themselves.
1 . 1 Cause of C hemical C omb ination
The atoms interact with each other on account of the following reasons :
(i) Decrease in energy : It is a fundamental truth that all natural systems tend to lose
potential energy and become more stable. Other things being equal, a system that has stored
potential energy is less stable than a system that has none. It is an observed fact that a
bonded state is more stable than unbonded stable. This is due to the fact that the bonded
state has lower potential energy than unbonded state. Hence, when two atoms approach
each other, they combine only under the condition that there is a decrease in potential
energy.
When two atoms approach each other, new forces of attraction and repulsion come into play.
The forces of attraction are between the nucleus of one atom and the electrons of the other.
The forces of repulsion are between two nuclei as well as between the electrons of the two
atoms. If the net result is attraction, the total potential energy of the system decreases and
a chemical bond results. No chemical bonding is possible if net result is repulsion.
(ii) Lewis octet rule : The noble gases are known for their lack of chemical activity. There are
no known compounds of helium, neon and argon. Why are these elements so unreactive
CHEMICAL BONDING
, 4 MARKS
towards other elements ? All these elements have electronic structures that consist of filled
outermost sheels. Except for helium, whose electronic configuration is 1s2, the s-and p-
subshells of the highest energy level contain a total of eight electrons. It is, therefore,
concluded that s2p6 configuration in the outer energy level constitutes a-structure of maximum
stability and therefore, of minimum energy.
The atoms of all elements when enter into chemical combination try to attain noble gas
configuration, i.e., they try to attain either 2 electrons (when only one energy shell) or 8
electrons in their outermost energy level which is of maximum stability and hence of minimum
energy. The tendency of atoms to achieve eight electrons in their outermost shell is known
as Lewis octet rule. Octet rule was the basis of electronic theory of valency.
1 . 2 L ewis Symb ols of E lement s
Chemical bonding mainly depends on the number of electrons present in the outermost energy
level. These electrons are termed as valency electrons. The electronic configuration of sodium (Na)
is 2, 8, 1 and that of sulphur has (S) 2, 8, 6. Thus, sodium has one valency electron while sulphur
has six valency electrons.
The valency electrons in atoms are shown in terms of Lewis symbols. To write Lewis symbol for
an element, we write down its symbol surrounded by a number of dots of crosses equal to the
number of valency electrons. Paired and unpaired valency electrons are also indicated. The Lewis
symbols for hydrogen, sodium, nitrogen, oxygen and chlorine may be written as :
H Na N O Cl
Generalised, Lewis symbols for the representative elements are given in the following table :
1 2 13 14 15 16 17
Group IA IIA IIIA IVA VA VIA VIIA
Lewis symbol X X X X X X X
1 . 3 E lect r onic t heor y of Valency
The theory of valency explains chemical combination in terms of electrons. The theory was
developed independently by W. Kossel and G.N. Lewis (1916) and extended by Irving Langmuir
(in 1919).
The chemical behaviour of an atom is determined to a large extent by the number and arrangement
of electrons in the outer orbitals of the atom. Only these electrons are involved in chemical
combination and so these are called the valence electrons.
CHEMICAL BONDING
