Valence Concept and Orbital Concept – Concepts of chemical bonding

Explain the two concepts, which explain the chemical bonding?

ANSWER:
There are two concepts, which explain chemical bonding.
A. The Valence Concept
B. The Orbital Concept

The Valence Concept (Electric theory of valence)

INTRODUCTION:
G.N Lewis and W. Kossel in 1916, gave the electronic theory of valence.

The Valence Concept:

STATEMENT:
It states that,
“In the formation of a chemical bond, atoms take part by losing, gaining or sharing of electrons to attain the inert or noble gas electronic configuration”
EXPLANATION:
• When atoms have two or eight electrons in their outermost shell, they are stable.
• The electron theory of valence can be explained named as Octet or Duplet’s theory of valance.
A. Octet Theory Of Valence / Rule Of Eight:
“The tendency of atoms to attain eight electrons in its valence shell in order to attain stability.”
EXAMPLE:
I. Oxygen (O) has six electrons in its valence shell.
II. It shares or gains two electrons in its outermost shell and attains stability by completing its outermost shell with eight electrons.
This is also known as The Octet rule or the rule of eight.
Duplet Rule/Rule Of Two:
“The tendency of atoms to attain two electrons in its valance shell in order to attain stability.”
EXAMPLE:
• Helium (He) has two electrons in its valence shell and is stable.
• The elements of group 8 of the periodic table, such as helium, neon and argon are known as Noble Gases.
• They are also known as Inert Gases because they are very stable and rarely take part in chemical reactions to form compounds.
• Their stability comes from their completely filled outer shell.
• Except for Helium which has two electrons in its outermost shell, all other noble gasses have their outermost shell filled with eight electrons.
• A shell with eight electrons is called an Octet and is very stable.
• Thus, when atoms take part in chemical reactions, they tend to combine in ways to complete eight electrons in their outermost shell, to attain the electronic configuration of the noble gasses. (except Helium)
The Orbital Concept:
I. This concept is based on the combination of atomic orbital to produce molecular orbital.
II. The atomic orbital has one electron.
III. These orbitals when coming close to one another, overlap each other.
IV. This overlapping is either Endwise or Sidewise.
V. Endwise overlapping produces Sigma Bond.
VI. Sidewise overlapping produces Pi-Bond.


Octet rule and duplet rule
Sigma bond and pi bond formation

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