Chemical Bonding & Shapes: Types, Forces, VSEPR, Hybridization

## **What is Chemical Bonding?**
Atoms combine to form compounds because they want to achieve **stability** (like a full outer shell). This combining is called **chemical bonding**. There are three main types:

### **1. Ionic Bonding**
- **Definition**: Bond formed by **transfer of electrons** from a metal to a non-metal.
- **How it works**:
  - Metal (low electronegativity) **loses** electrons → becomes **cation** (positive ion).
  - Non-metal (high electronegativity) **gains** electrons → becomes **anion** (negative ion).
  - Opposite charges attract → **ionic bond** forms.
- **Example**: Sodium (Na) + Chlorine (Cl) → NaCl (sodium chloride).
  figure
{"type":"molecule","formula":"H2O","show":"all","highlight":[{"atom":"O","lonePairs":2}]}

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Hybridization of Orbitals

Atoms mix (hybridize) orbitals to explain molecular shapes and bond angles.

Example: CH₄ (Methane)

• Carbon (C) has 2s¹ 2p² → needs 4 bonds.
• sp³ hybridization: 1 s + 3 p orbitals mix → 4 sp³ hybrid orbitals.
• These orbitals arrange tetrahedrally → 109.5° bond angles.

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Intermolecular Forces (Weaker than Bonds!)

These forces hold molecules together (not atoms within a molecule).

Why is water liquid at room temperature?

• Hydrogen bonding between H₂O molecules requires more energy to break than London forces in similar-sized molecules (e.g., H₂S is a gas).

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Exam Tip: How to Score Full Marks

1. Draw diagrams for shapes (VSEPR) and hybridization—label bond angles!
2. Compare ionic vs. covalent in tables (properties, conductivity, etc.).
3. Explain hybridization with orbital mixing (e.g., sp³ for CH₄).
4. Predict shapes using VSEPR:
   • Count bonding (B) + lone pairs (L).
   • Use B:L ratio to pick shape from the table above.
5. For NEB questions:
   • Short answers: Define ionic/covalent/metallic bonding.
   • Long answers: Explain VSEPR + hybridization for a given molecule (e.g., NH₃).

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Solved Examples

Example 1: Predict the shape of PCl₅.

• Step 1: Draw Lewis structure → 5 bonding pairs, 0 lone pairs.
• Step 2: VSEPR predicts trigonal bipyramidal.
• Step 3: Hybridization → sp³d (1 s + 3 p + 1 d).

Example 2: Why does NaCl have a high melting point?

• Answer: NaCl is ionic → strong electrostatic forces in a 3D lattice require lots of energy to break.

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NEB Board-Style Questions

Q1. (Short Answer) Define: a) Ionic bond b) Covalent bond c) Hybridization

Q2. (Long Answer) a) Explain VSEPR theory with examples of linear, bent, and tetrahedral shapes. b) Draw the shape of NH₃ and explain its bond angle.

Q3. (Numerical) Calculate the bond angle in H₂O using VSEPR theory. Why is it less than the tetrahedral angle?

Q4. (Comparison)

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Key Formulas to Remember

1. Formal Charge (for Lewis structures): $$\text{Formal Charge}=(\text{Valence e⁻})-(\text{Non-bonding e⁻})-\frac{1}{2}(\text{Bonding e⁻})$$
2. Hybridization Rules:
   • 2 regions (B + L): sp
   • 3 regions: sp²
   • 4 regions: sp³
   • 5 regions: sp³d
   • 6 regions: sp³d²

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Summary Table: Bonding Types

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