Atoms are the building blocks of matter. Under normal conditions no atom exists as an independent (single) entity in nature, except the noble gases. A group of atoms that exists together as one species is called a molecule, and the attractive force that holds the atoms together is called a bond. A chemical bond is the force of attraction between the atoms that binds them together as a unit called a molecule.
1. Kossel-Lewis Approach and the Octet Rule
Kossel and Lewis explained why atoms combine based on the electronic configuration of noble gases. Noble gas atoms have little or no tendency to combine with each other or with atoms of other elements, so they must have stable electronic configurations.
| Noble gas | 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 | eight valence electrons |