What are chemical bonds?
The chemical bond is defined as the force which holds or binds the atoms/ ions together in a molecule.
Before the electronic
configuration consideration, the binding force which holds the atoms together
in a molecule is considered as the binding capacity of atoms that is known as
valency.
Valency
It is defined as the binding capacity of an
atom to make a bond with other elements. For example, The valency of hydrogen
is 1 and the valency of oxygen is 2. This concept is considered the classical
concept of bonding. Now many modern theories replace this classical concept of
bonding. Many other forces besides electrostatic forces of attraction are
responsible for chemical bonding. These areas follow:
- Dipole-dipole
forces
- Ion-dipole
forces
History
of chemical bonding
Thomson suggested that the forces of the attraction between the differently charged atoms are responsible for chemical
bonding.
Kossel in 1916 gave two postulates
1.
He said that the atoms which are more
electropositive followed the inert gases electronic configuration and loses
their electrons to produce positively charged ions, which have inert gas
electronic configuration.
2.
On the other hand, the atoms which are strong
electronegative also follow the noble
gases and able to gain electrons and become negatively charged ions which have
the electronic configuration of noble gases.
The bond which is formed
between positive and negative ions is known as an ionic bond.
Lewis
in 1916 suggested that some chemical bonds are formed by the sharing of
electrons between two atoms. This bond is known as a covalent bond.
How atoms make a chemical bond
Atoms make chemical bonds
to form molecules to get stability. When atoms combine with each other to make
molecules, they come close to each other in such a way that the energy of the system is lowered. During the formation of a bond, the energy of the molecule falls
due to attractive forces.
When atoms come close to
each other, the energy of the whole system continuously decreases up to a point
where repulsion between the nucleus becomes minimum and now the energy of the system goes
upward. The energy is minimum when both the atoms have equilibrium internuclear distance and both the
atoms are held together more tightly with the maximum decrease in energy. The energy
present this time is less than the energy of atoms in individuals' forms. Now at
this point stability is gained and chemical bonds will be formed between them to
form molecules.
When atoms come close to
each other, three types of forces operate at that time.
- Attractive forces between the electron of one atom and the nucleus of other atoms.
- Repulsive forces between the electrons of both atoms because electrons
have a negative charge and negative-negative repel each other.
- Repulsive forces between the nucleus of both atoms because nucleus have a positive
charge so positive-positive also repel each other.
The chemical bond is formed when attractive forces dominate the other
two forces.
Why atoms make chemical bonds
Atoms make chemical bonds
to get stability by attaining the electronic configuration of noble gases.
Noble gases are considered as stable elements of the periodic table and these
elements are less reactive. All the other elements of the periodic table try to
attain the noble gas electronic configuration.
To attain noble gas
electronic configuration two rules are followed.
Ø Duplet rule
Ø Octet rule
Duplet
rule
To attain 2 electrons on their outermost shell
is known as the duplet rule.
Only elements of the period
no 1 (hydrogen and helium) follow this rule because they have only one shell.
Octet
rule
To attain 8 electrons in
their outermost shell is known as the octet rule.
All the other elements of the periodic table
follow the octet rule.
Types of chemical bonding
o Metallic bond
o Hydrogen bonding
o Electron deficient molecules
o Vander Waal's forces
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