B Tech Applied Science: Unit 1 Chemistry - Covalent Bonds

Overview

• Focus on covalent bonds
• Recap: Ionic bonds involve swapping of electrons, while covalent bonds involve sharing.

Covalent Bond Basics

• Definition: Atoms share electrons to achieve a full outer shell.
• Example: Chlorine molecule (Cl₂)
  • Each chlorine atom shares one electron to complete their outer shell.
  • Represented by a dot and cross diagram.

Dot and Cross Diagrams

• Visual representation of shared electrons in molecules.
• Examples:
  • Ammonia (NH₃): Nitrogen shares electrons with three hydrogens.
  • Methane (CH₄): Forms a tetrahedral shape, important in organic chemistry.
  • Carbon Dioxide (CO₂): Involves double bonds between carbon and oxygen.

Types of Covalent Bonds

• Single bond: Sharing of one pair of electrons.
• Double bond: Sharing of two pairs of electrons.
• Triple bond: Sharing of three pairs of electrons.
• Dative covalent bond (Coordinate bond): Both shared electrons come from the same atom. Example: Ammonium ion (NH₄⁺).

Strength of Covalent Bonds

• Factors influencing strength:
  • Bond length: Shorter bonds are stronger.
  • Number of shared electrons: Single < Double < Triple in strength.

Electronegativity

• Definition: Tendency of an atom to attract bonding electrons.
• Electronegativity Trends:
  • Increases across a period (left to right).
  • Decreases down a group (top to bottom).
• Fluorine: Most electronegative element.

Types of Covalent Bonds Based on Electronegativity

• Pure covalent bond: Equal sharing of electrons (no difference in electronegativity).
• Polar covalent bond: Unequal sharing, results in a dipole (difference 0.4 - 2.0).
  • Example: Hydrogen fluoride (HF) and water (H₂O).
• Ionic bond: Complete electron transfer (difference > 2.0).

Practice Questions

• Draw dot and cross diagrams for:
  • Hydrogen sulfide (H₂S)
  • Hydroxide ion (OH⁻)
  • Nitrate ion (NO₃⁻) involving a dative bond

Additional Points

• Electronegativity Chart: Important for understanding bond types.
• Significance of Water (H₂O): Example of a polar molecule, important in future studies.

Recommended Further Study

• Watch additional videos on covalent bonding for a deeper understanding.