Covalent Bonds and Their Representations

Introduction

• Covalent Bonds
  • Formed by sharing electrons between atoms.
  • Different from ionic bonds where electrons are transferred.

Ionic Bonds Recap

• Ionic bonds form when electrons are transferred, leading to oppositely charged ions attracting each other.
  • Example: Sodium and Chlorine.

Covalent Bond Formation

• Occurs in non-metal elements (e.g., two chlorine atoms).
  • Atoms share electrons to achieve full outer shells.
  • Example: Each chlorine atom shares one electron.

Representation of Covalent Bonds

Dot and Cross Diagrams

• Used to visualize which electrons belong to which atom.
• Only outermost shells are drawn unless specified otherwise.
• Atoms represented by dots and crosses to distinguish shared electrons.

Displayed Formula

• Chemical symbols of atoms joined by lines.
• Easier for larger molecules like glucose.
• Limitation: Does not show 3D shape of molecules.

3D Models

• Show actual arrangement of atoms.
• More complex to predict shapes.

Example: Ammonia (NH3)

• Molecular formula indicates one nitrogen and three hydrogen atoms.
• Steps for Covalent Bonding:
  1. Draw out atoms (outermost shells).
  2. Each hydrogen needs one extra electron; nitrogen needs three.
  3. Hydrogen shares electrons with nitrogen for full outer shells.
  4. Draw as a dot and cross diagram or displayed formula.

Types of Substances Formed by Covalent Bonds

Simple Molecular Substances

• Atoms joined by strong covalent bonds.
• Weak intermolecular forces between molecules.
• Examples: Chlorine, Ammonia, Water (H2O), Methane (CH4).

Polymers and Giant Covalent Structures

• Polymers: Long chains of repeating units (monomers).
  • Used in plastics and textiles.
• Giant Covalent Structures: Include silicon dioxide, diamond, graphite.
  • Strong due to extensive covalent bonding in a lattice.

Conclusion

• Covalent bonds result in various molecular substances ranging from simple molecules to complex structures.
• Understanding of drawing methods is crucial for visualizing molecular structures.