1. Ionic Bond
A sodium atom loses an electron from its last shell and forms a cation. The cation, now, has the neon configuration, [Ne]. This configuration is very stable since it corresponds to a noble-gas configuration. The chlorine atom, on the other hand, receives the electron from the sodium atom, itself attaining the argon configuration [Ar]. This configuration is also very stable, corresponding to a noble-gas configuration.
It is the stability of the ions that ultimately lead to the formation of the ionic solid, NaCl. Once a cation or an anion is formed, it starts to attract oppositely charged ions immediately. This attraction improves stability furthermore, attaining the crystal structure ultimately. The ionic solid represents the lowest energy level, and therefore maximum stability.

2. Covalent Bond

3. Orbitals in Covalent Bond

4. Bond Energies

5. Lewis Dot Symbols
Each element is shown by its elemental symbols and valence electrons only

6. Formation of Hydrogen Chloride
1bonding pair : H Cl H Cl
3 lone pairs
When the atoms combine, they form a stable covalent bond. This bond is a single bond, denoted by a single line between the two atoms. Each single bond represents a pair of electrons. By sharing a pair of electrons, hydrogen is surrounded by two and chlorine is surrounded by eight valence electrons.

7. Electronegativities of Elements

8. Formation of Hydrogen Fluoride

9. Interference of Waves
Constructive
Destructive

10. Shapes of Orbitals

11. Structure of Methane

12. sp3 Hybridisation

13. Common Hybridisations

14. Arrangement of Electron Pairs

15. Molecular Shapes

16. Molecular Shapes