NEET Notes: Chemical Bonding and Molecular Structure

Introduction

Chemical Bonding and Molecular Structure is a crucial chapter in chemistry that explains how atoms combine to form molecules and compounds. It deals with the different types of chemical bonds, their formation, and the properties of molecules based on their structure. Understanding this chapter helps in predicting the behavior of substances in various chemical reactions.

Fundamental Concepts of Chemical Bonding

1. Importance of Chemical Bonding

Chemical bonding explains how elements come together to form compounds with specific properties. It helps in:

• Understanding the stability of molecules.

• Predicting molecular shapes and structures.

• Explaining chemical reactions and interactions between molecules.

Types of Chemical Bonds

1. Ionic Bond

An ionic bond is formed when one atom transfers electrons to another, resulting in the formation of positively and negatively charged ions. The electrostatic attraction between these oppositely charged ions holds them together.

Characteristics of Ionic Bonds:

• Formed between metals and non-metals.

• High melting and boiling points.

• Conduct electricity in molten or aqueous states.

• Soluble in polar solvents like water.

2. Covalent Bond

A covalent bond is formed when two atoms share one or more pairs of electrons to achieve stability.

Types of Covalent Bonds:

• Single Covalent Bond: Involves the sharing of one pair of electrons.

• Double Covalent Bond: Involves the sharing of two pairs of electrons.

• Triple Covalent Bond: Involves the sharing of three pairs of electrons.

Properties of Covalent Compounds:

• Low melting and boiling points.

• Poor conductors of electricity.

• Soluble in non-polar solvents like benzene.

3. Coordinate Bond (Dative Bond)

A coordinate bond is a type of covalent bond where one atom donates both electrons to form the bond.

Examples:

• Formation of ammonium ion (NH₄⁺).

• Formation of hydronium ion (H₃O⁺).

Concepts Related to Chemical Bonding

1. Lewis Structure

Lewis structures, also known as electron dot structures, represent the valence electrons of atoms in a molecule. They help in understanding:

• The arrangement of atoms in a molecule.

• The type of bonding between atoms.

• The presence of lone pairs and multiple bonds.

2. VSEPR Theory (Valence Shell Electron Pair Repulsion Theory)

VSEPR theory helps in predicting the shape of molecules based on the repulsion between electron pairs.

Common Molecular Shapes:

• Linear (180°) – Example: CO₂

• Trigonal Planar (120°) – Example: BF₃

• Tetrahedral (109.5°) – Example: CH₄

• Trigonal Bipyramidal (90° and 120°) – Example: PCl₅

• Octahedral (90°) – Example: SF₆

3. Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals with equivalent energy.

Types of Hybridization:

• sp Hybridization: Linear shape, Example: BeCl₂

• sp² Hybridization: Trigonal planar shape, Example: BF₃

• sp³ Hybridization: Tetrahedral shape, Example: CH₄

• sp³d Hybridization: Trigonal bipyramidal shape, Example: PCl₅

• sp³d² Hybridization: Octahedral shape, Example: SF₆

4. Molecular Orbital Theory (MOT)

Molecular Orbital Theory explains the formation of molecular orbitals by the combination of atomic orbitals.

Key Points of MOT:

• Bonding molecular orbitals are lower in energy and stable.

• Anti-bonding molecular orbitals are higher in energy and unstable.

• Bond order determines the stability of a molecule.

5. Polarity of Molecules

Molecular polarity is determined by the difference in electronegativity between atoms and the molecular shape.

Types of Molecules:

• Polar Molecules: Unequal sharing of electrons, Example: H₂O

• Non-Polar Molecules: Equal sharing of electrons, Example: O₂

Intermolecular Forces

1. Dipole-Dipole Interaction

Attraction between polar molecules due to their permanent dipoles. Example: HCl

2. Hydrogen Bonding

Strong attraction between hydrogen and highly electronegative elements (F, O, N). Example: Water (H₂O)

3. London Dispersion Forces (Van der Waals Forces)

Weak forces present in non-polar molecules due to temporary dipoles. Example: Noble gases

Applications of Chemical Bonding in NEET and Real Life

1. In NEET Exam: Questions based on bond formation, hybridization, molecular geometry, and polarity frequently appear.

2. In Pharmaceuticals: Chemical bonding concepts help in designing drug molecules and understanding molecular interactions.

3. In Material Science: Helps in explaining properties of metals, ceramics, and polymers.

4. In Biology: Explains biochemical interactions like hydrogen bonding in DNA.

Conclusion

Chemical Bonding and Molecular Structure is a fundamental topic in Chemistry. It helps in understanding how atoms combine to form stable molecules, their shapes, and their properties. Mastering this chapter is essential for solving conceptual and numerical problems in NEET Chemistry.