Covalent Bonding: Sharing Electrons, Drawing Methods, and Types of Substances

Introduction

In this article we explore how non‑metal atoms form covalent bonds by sharing electrons, the various ways to represent these bonds on paper, and the different categories of substances that rely on covalent bonding.

Quick Recap: Ionic Bonds

• Ionic bonds occur when one atom transfers electrons to another.
• The transfer creates oppositely charged ions that attract each other.
• This mechanism works best when one atom has excess electrons (e.g., Na) and the other lacks them (e.g., Cl).

What Is a Covalent Bond?

• When two non‑metals need an extra electron each, sharing is more efficient than transferring.
• Each atom contributes one electron, resulting in a pair of shared electrons that count toward the outer shell of both atoms.
• The shared pair is the essence of a covalent bond.

Ways to Draw Covalent Bonds

1. Dot‑and‑Cross Diagrams
2. Use dots for one atom’s valence electrons and crosses for the other’s.
3. Shows exactly which electrons belong to which atom.
4. May require drawing all electron shells if the problem asks for it.
5. Displayed Formulas
6. Write element symbols and connect them with lines representing shared electron pairs.
7. Ideal for larger molecules where dot‑and‑cross diagrams become cumbersome.
8. Example: the structural formula of glucose (C₆H₁₂O₆) is shown with lines only.
9. 3‑D Models
10. Illustrate the spatial arrangement of atoms.
11. Do not convey electron details but give insight into molecular geometry.
12. Useful for visualising shapes such as tetrahedral, trigonal pyramidal, etc.

Step‑by‑Step Example: Ammonia (NH₃)

• Molecular formula: NH₃ (one nitrogen, three hydrogens).
• Outer‑shell capacities:
• Hydrogen: 2 electrons (needs 1 more).
• Nitrogen: 8 electrons (needs 3 more).
• Bond formation: Each hydrogen shares its one electron with nitrogen, giving nitrogen three shared pairs and each hydrogen a full shell.
• Representations:
• Dot‑and‑Cross: Draw outer shells, place dots on H, crosses on N, connect shared electrons.
• Displayed Formula: N—H, N—H, N—H (three single lines).
• 3‑D Model: Trigonal‑pyramidal shape with nitrogen at the apex.

Types of Substances Formed by Covalent Bonds

• Simple Molecular Substances
• Small, discrete molecules (e.g., Cl₂, NH₃, H₂O, CH₄).
• Strong covalent bonds within molecules, weak intermolecular forces between them.
• Polymers
• Long chains of repeating monomers linked by covalent bonds.
• Examples: plastics, nylon, polyester.
• Giant Covalent (Network) Structures
• Vast lattices where every atom is covalently bonded to many neighbours.
• Examples: silicon dioxide (glass), diamond, graphite.
• Extremely high melting points and hardness due to the extensive bonding network.

Where to Find More Help

• All videos, practice questions, flashcards, and progress tracking are available at cognito.org.
• Free sign‑up gives access to a full playlist on YouTube and additional study resources.

Summary of Key Points

• Covalent bonds involve sharing, not transferring, electrons.
• Three common drawing methods: dot‑and‑cross, displayed formula, and 3‑D model.
• Substances range from simple molecules to massive network solids.
• Understanding these concepts prepares you for more advanced topics like polymers and crystal lattices.

Covalent bonding lets non‑metal atoms achieve full outer shells by sharing electrons, and mastering the various ways to represent these bonds—dot‑and‑cross diagrams, displayed formulas, and 3‑D models—provides a solid foundation for studying everything from simple molecules to complex polymers and network solids.