Grade 10 general science Matter and Chemical Reactions – Chemical bonding Notes
Matter & Chemical Reactions — Subtopic: Chemical Bonding
Subject: General Science | Target age: 15 (Kenya)
- Illustrate chemical bonding in common compounds.
- Identify bond types in common compounds.
- Distinguish structures of selected elements and compounds.
- Describe how bond types affect physical properties.
- Select materials for use based on bond type & structure.
- Reflect on appropriateness of substances used in daily life.
1. What is chemical bonding?
Atoms join together by sharing or transferring electrons to form substances. The way electrons are shared or transferred gives rise to different bond types. Bond type explains many properties of materials you use every day (salt, sugar, metals, glass, plastics).
2. Main types of bonds (with simple illustrations)
Ionic bond (transfer of electron)
Formed between a metal and a non-metal. One atom gives electrons, the other takes them → charged ions attract.
Na
Sodium (Na)
➜ transfer e⁻ ➜
Cl
Chlorine (Cl)
Na⁺ Cl⁻ → NaCl (salt)
Properties: high melting point, brittle, soluble in water, conducts electricity when molten or in solution.
Covalent bond (sharing of electrons)
Two non-metals share pairs of electrons. Can be simple molecules (H2O, CO2) or large molecular chains (polymers like plastics).
O
H
H
H–O–H (water): electrons shared between O and each H
Properties: lower melting/boiling points for many covalent molecules, poor electrical conductors (except acids/bases when ionized), many are gases or liquids at room temp; large covalent networks (diamond, silica) are hard and have high melting points.
Metallic bond (sea of electrons)
Metal atoms release some electrons that move freely (delocalized). Positive metal ions are held together by these free electrons.
Cu⁺⁺
e⁻ free
Example: copper wires, iron nails. Properties: good electrical & heat conductors, shiny (lustre), malleable and ductile (can be hammered or drawn into wires).
Network covalent / giant structures
Atoms covalently bonded in a giant 3D network (e.g., diamond, silica/ glass). Very hard, very high melting points, often do not conduct electricity.
Examples:
- Diamond — carbon atoms in 3D network (very hard).
- Graphite — layers of carbon with weak forces between layers (soft, conducts along layers; used in pencils).
- Glass (silica) — network covalent/ionic mixture used in windows and bottles.
3. How structure relates to physical properties (quick guide)
Ionic solids
High mp, brittle, soluble in water (often), conduct when molten/aqueous.
High mp, brittle, soluble in water (often), conduct when molten/aqueous.
Covalent molecules
Low to moderate mp, many are gases/liquids/solids, poor conductors.
Low to moderate mp, many are gases/liquids/solids, poor conductors.
Metallic
Malleable, ductile, shiny, good conductors of heat & electricity.
Malleable, ductile, shiny, good conductors of heat & electricity.
Network covalent
Very hard, high mp, usually poor electrical conductors (except graphite).
Very hard, high mp, usually poor electrical conductors (except graphite).
4. Common Kenyan examples — bonding and why they are used
- Table salt (NaCl) — ionic: dissolves in water, used in cooking and preserving food.
- Sugar (sucrose) — covalent molecular: soluble in water, does not conduct electricity.
- Copper wires — metallic: excellent electrical conductor for household wiring.
- Aluminium cooking pots — metallic: lightweight, conducts heat well.
- Glass windows — network covalent/ionic: hard, transparent, heat resistant for many uses.
- Ceramic cooking pots (earthenware) — ionic/covalent solid: heat resistant, used for cooking locally.
- Plastic jerrycans and spoons — covalent polymer: light, does not conduct electricity, chemically resistant (but some plastics can degrade in heat).
- Pencil lead (graphite) — layered covalent: soft, leaves marks, conducts electricity along layers.
5. Simple classroom activities (safe & age-appropriate)
-
Conductivity test:
- Set up a simple circuit (battery, bulb, wires). Test: solid salt (no), salt solution (yes), sugar solution (no).
- Conclusion: ionic compounds give ions in solution → conduct electricity.
-
Solubility & melting behaviour:
- Compare how much salt and sugar dissolve in water and how they behave on heating (sugar caramelizes; salt does not melt easily in the flame).
-
Metal tests:
- Compare metal vs plastic spoon: tap, bend slightly to observe malleability; test which conducts heat faster (careful with safety).
Safety note: perform experiments under teacher supervision. Do not taste unknown chemicals; use gloves and goggles when heating or using electricity.
6. How to choose materials based on bonding & structure
- Need good electrical conductor? Choose metals (copper, aluminium) — metallic bonds give free electrons.
- Need heat-resistant, hard material (e.g., some kitchenware, tiles)? Use ceramics or glass — network structures resist heat.
- Need light, non-conducting container (e.g., jerrycan for water)? Use plastics — covalent polymers are insulating.
- Choose stainless steel or coated metals where corrosion resistance and strength are needed (nails, tools).
7. Reflection activity (class / homework)
List five items you use at home. For each:
- Name the item (e.g., cooking pot).
- Identify the main material (e.g., aluminium).
- Suggest the bond type (metallic, ionic, covalent, network) and explain one reason why that bond type makes the material suitable for the use.
Example: Copper wire — metallic bond → conducts electricity well → good for household wiring.
8. Quick assessment questions
- Is NaCl ionic or covalent? Give one property that supports your answer.
- Why are metals used for cooking pots and pans?
- Explain why sugar does not conduct electricity in water but salt does.
- Compare diamond and graphite: both are carbon — why do they have different properties?
Answers (click to view)
- NaCl is ionic. Property: conducts electricity when dissolved or molten (because ions move).
- Metals are used because metallic bonds give high thermal conductivity and metals are strong and malleable.
- Salt forms ions in water that carry charge; sugar dissolves as neutral molecules and does not provide ions.
- Diamond: each carbon bonded to four others in 3D (very hard, no free electrons). Graphite: carbons in layers with delocalised electrons (soft layers, conducts electricity along layers).