### Theory:

Bond:

As we already know, Atoms are the basic structural units of matter. Except for noble gases, no atom in nature exists as an independent (single) entity under normal conditions.

On the other hand, a set of atoms is discovered to exist as a single species. A molecule is a collection of atoms. A force should hold the constituent atoms together; just like thread has the flowers in a garland together. So we can say,
A bond is an attractive force that holds the atoms together.
Garland

Chemical bond:
A chemical bond may be defined as the force of attraction between the atoms that bind them together as a unit called a Molecule.
Linear bonding

We will learn about the Kossel-Lewis approach to chemical bonds, the Lewis dot structure, and various reactions in this unit.

Kossel - Lewis approach to chemical bonds:

Chemical compounds are formed when atoms of various elements interact in multiple ways. Many questions were raised as a result of this phenomenon.
• Why do atoms come together?
• How do atoms come together?
• What makes certain atoms unite and others don't?
Various ideas have been proposed from time to time to answer such questions. One such idea is Kossel-Lewis theory, which explains the production of molecules.

Kossel and Lewis approach:
Atoms combine to form molecules was successfully explained by Kossel and Lewis using the concept of an electronic configuration of noble gases. Noble gas atoms have a small or no tendency to mix with other noble gas atoms or atoms of other elements. This approach implies that the electronic configuration of these atoms must be stable.
The electronic configurations of noble gases:

 Name of the element Atomic number Shell electronic configuration Helium (He) $$2$$ $$2$$ Neon (Ne) $$10$$ $$2$$, $$8$$ Argon (Ar) $$18$$ $$2$$, $$8$$, $$8$$ Krypton (Kr) $$36$$ $$2$$, $$8$$, $$18$$, $$8$$ Xenon (Xe) $$54$$ $$2$$, $$8$$, $$18$$, $$18$$, $$8$$ Radon (Rn) $$86$$ $$2$$, $$8$$, $$18$$, $$32$$, $$18$$, $$8$$

1. All noble gases (except for Helium), have eight electrons in their valence shell. Therefore, no additional electrons can be added.
2. The noble gas atoms do not tend to gain or lose electrons due to their stable valence shell electronic configuration, so their valency is zero.
3. They're so inert that they don't even form diatomic molecules. Instead they preferer to live as monoatomic gaseous atoms.