Chapter 4: Structure of Molecules

Introduction:
All matter is composed of atoms. When atoms combine, they form molecules. This chapter explains how atoms bond together and how molecules are structured.

Key Concepts:

• Atom: The smallest particle of an element retaining its properties.
• Molecule: A group of two or more atoms held together chemically.
• Chemical Bond: The force that holds atoms together in a compound.

Types of Chemical Bonds:

1. Ionic Bond: Formed when atoms transfer electrons (e.g., NaCl).
2. Covalent Bond: Formed when atoms share electrons (e.g., H₂O).
3. Coordinate Bond: One atom donates an electron pair to another (e.g., NH₄⁺).
4. Metallic Bond: Found in metals; electrons are delocalized (e.g., Cu, Fe).

Valency:

Valency is the combining capacity of an atom. Example: Oxygen has valency 2.

Lewis Structure:

Shows valence electrons as dots to represent bonding between atoms.

VSEPR Theory:

This theory predicts molecular geometry. Example: H₂O is bent, CH₄ is tetrahedral.

Polarity:

Some molecules have unequal charge distribution (H₂O is polar, O₂ is nonpolar).

Long Questions:

1. Differentiate between Ionic and Covalent bonds.
2. Explain VSEPR theory with examples.
3. What is a Lewis structure? Illustrate with examples.

Short Questions:

1. Define valency.
2. Give one example of a metallic bond.
3. Differentiate between polar and nonpolar molecules.

MCQs:

1. What type of bond is present in NaCl? (Ionic)
2. What is the shape of H₂O molecule? (Bent)
3. Which atom is central in CH₄? (Carbon)
4. How many covalent bonds are there in NH₄⁺? (3)
5. What does VSEPR stand for? (Valence Shell Electron Pair Repulsion)