GCSE Chemistry • Topic 2

Bonding, Structure & Properties

How atoms join together and how bonding determines properties.

📌 What You’ll Learn

  • Why atoms bond (electron configuration)
  • Ionic, covalent, and metallic bonding
  • Simple molecular vs giant structures
  • Properties explained using bonding
  • Nanoparticles (advantages & risks)

🧠 How to Study

  • Always start with outer shell electrons
  • Link structure → properties (never separate)
  • Draw dot-and-cross diagrams neatly
  • Memorise keywords used in explanations
1. Why Atoms Bond (Foundation)

Stability is the Goal

Atoms bond to achieve a stable electronic structure. Noble gases (Group 0) are already stable because they have a full outer shell.

Other atoms must either transfer or share electrons to get a full outer shell.

⚠️ Exam Trap

Never say atoms "want to be happy". Say "Atoms bond to achieve a stable electronic structure (full outer shell)."

Q1: Why are Noble Gases unreactive?

They have a full outer shell of electrons, making them stable.

2. Ionic Bonding (Metal + Non-metal)

Electron Transfer

Ionic bonding occurs between a metal and a non-metal. The metal loses electrons to become a positive ion ($+$), and the non-metal gains electrons to become a negative ion ($-$).

[Image of dot and cross diagram for NaCl]

Definition: The strong electrostatic force of attraction between oppositely charged ions.

Properties of Ionic Compounds

  • High Melting Points: Requires lots of energy to break strong electrostatic forces.
  • Conductivity: Conducts electricity only when molten or dissolved because ions are free to move and carry charge.
  • Brittle: Layers shift and like-charges repel, breaking the lattice.

Q1: Explain why NaCl has a high melting point.

It has a giant ionic lattice with strong electrostatic forces of attraction between oppositely charged ions, which requires a large amount of energy to overcome.

3. Covalent Bonding (Non-metal + Non-metal)

Electron Sharing

Covalent bonding occurs between non-metals. They share pairs of electrons to achieve full outer shells.

Simple Molecular Substances

Examples: $H_2$, $O_2$, $H_2O$, $CO_2$.

  • Low melting/boiling points: They have weak intermolecular forces between molecules that don't need much energy to break.
  • Do not conduct: Molecules are neutral (no free electrons or ions).
⚠️ Exam Trap

Do NOT say covalent bonds are weak. The covalent bonds are strong, but the intermolecular forces are weak. It is the intermolecular forces that break during boiling.

4. Structure & Properties (Giant Structures)

4.1 Giant Covalent Structures

Every atom is joined to others by strong covalent bonds in a massive lattice.

Structure Properties Reasoning
Diamond Hard, High MP Each Carbon forms 4 strong covalent bonds in a rigid structure.
Graphite Soft, Conducts 3 bonds per C. Delocalised electrons move between layers. Layers have weak forces between layers and can slide.
Graphene Strong, Conducts Single layer of graphite. Extremely strong and conductive. (Higher Tier enrichment; focus on diamond/graphite unless specified).

4.2 Metallic Bonding

Occurs in metals. Metallic bonding is the electrostatic attraction between positive metal ions and delocalised electrons.

  • Malleable: Layers of ions can slide over each other without breaking the metallic bond.
  • Conductive: Delocalised electrons are free to move through the structure and carry charge/thermal energy.

Q1: Why is graphite soft but diamond is hard?

Diamond has a rigid 3D lattice where every carbon has 4 strong covalent bonds. Graphite has layers with weak forces between them, allowing layers to slide.

5. Nanoparticles (Modern Tech)

The Power of Size

Nanoparticles have a diameter between 1 and 100 nm. They have a very high surface area to volume ratio.

[Image showing surface area to volume ratio for different sized cubes]
  • Uses: Catalysts, sunscreens (better coverage), medicine (targeted delivery).
  • Risks: They are so small they could enter cells or the brain; long-term health effects are unknown.

Q1: Why do nanoparticles make good catalysts?

Because they have a very high surface area to volume ratio, providing more space for reactions to occur.

⚡ Quick Revision Checklist

Bonding Types:
  • Ionic = Electron transfer (Metal + Non-metal)
  • Covalent = Electron sharing (Non-metals)
  • Metallic = Delocalised electrons (Metals)
Structure Logic:
  • Simple molecular → Low MP (weak forces)
  • Giant ionic/covalent → High MP (strong bonds)
  • Graphite conducts → Delocalised electrons

🚫 Brutal Exam Trap Summary

1. Don't confuse intermolecular forces with covalent bonds. Intermolecular = weak.
2. Don't say metals "share electrons"; they have a sea of delocalised electrons.
3. Don't forget that ionic compounds only conduct when molten or in solution.
4. Don't use the word "atoms" when talking about ionic conductivity; use "ions".

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