Introduction to Chemical Bonding
Chemical bonds are the attractive forces that hold atoms together in compounds. The main types are:
- Ionic Bonds
- Covalent Bonds
- Metallic Bonds
Ionic Bonding
Ionic bonds form when electrons are transferred from one atom to another.
Rule: Ionic bonds typically form between metals and non-metals.
Formation of NaCl
$$
\text{Na} \rightarrow \text{Na}^+ + e^-
$$
$$
\text{Cl} + e^- \rightarrow \text{Cl}^-
$$
$$
\text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl}
$$
Properties of Ionic Compounds
- High melting and boiling points
- Conduct electricity in molten state or solution
- Usually soluble in water
- Hard and brittle crystals
Covalent Bonding
Covalent bonds form when atoms share electrons.
Types of Covalent Bonds
| Type | Shared Pairs | Example |
|---|---|---|
| Single Bond | 1 | $H_2$ (H–H) |
| Double Bond | 2 | $O_2$ (O=O) |
| Triple Bond | 3 | $N_2$ (N≡N) |
Bond Energy Trend
$$
\text{Triple Bond} > \text{Double Bond} > \text{Single Bond}
$$
Lewis Dot Structure of Water
Water ($H_2O$) has:
- 2 bonding pairs
- 2 lone pairs
- Bond angle: 104.5°
VSEPR Theory
The Valence Shell Electron Pair Repulsion theory predicts molecular geometry.
Common Geometries
| Electron Pairs | Geometry | Example | Bond Angle |
|---|---|---|---|
| 2 | Linear | $BeCl_2$ | 180° |
| 3 | Trigonal Planar | $BF_3$ | 120° |
| 4 | Tetrahedral | $CH_4$ | 109.5° |
Key Formulas
Formal Charge:
$$
FC = V - N - \frac{B}{2}
$$
Where:
- $V$ = Valence electrons
- $N$ = Non-bonding electrons
- $B$ = Bonding electrons