Explain the two concepts, which explain the chemical bonding?
Chemical bonding is explained with the help of two important concepts.
- The Valence Concept
- The Orbital Concept
The Valence Concept (Electric theory of valence)
In 1916, G.N Lewis and W. Kossel presented the electronic theory of valence.
It states that “In a chemical bond formation, atoms take part by losing, gain or sharing of electrons, to attain the inert or noble gas electronic configuration”
- 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.
Octet Theory Of Valence / Rule Of Eight:
“The tendency of atoms to attain eight electrons in the outermost shell to attain stability.”
- Oxygen (O) has six electrons in its valence shell.
- It shares or gains two electrons in its outermost shell and attains stability by completing its outermost shell with eight electrons.
This is also named “The Octet rule or the rule of eight”.
Duplet Rule/Rule Of Two:
“The tendency of atoms to attain two valance electrons to attain stability.”
- 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 outermost 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:
- This concept is based on the combination of atomic orbital to produce molecular orbital.
- The atomic orbital has one electron.
- These orbitals when coming close to one another, overlap each other.
- This overlapping is either Endwise (head-on) or Sidewise.
- Endwise or head-on overlapping produces Sigma Bond.
- Sidewise overlapping produces Pi-Bond.