Grade 10 chemisty Inorganic Chemistry – Chemical Bonding Notes
Inorganic Chemistry — Chemical Bonding
Subject: Chemistry | Subtopic: Chemical Bonding | Age: 15 (Kenya)
- a) Explain the role of valence electrons in bonding (octet/duplet rule).
- b) Illustrate different bond types — ionic, covalent, dative (coordinate) covalent, hydrogen bond, Van der Waals forces, metallic — in elements, molecules and compounds.
- c) Construct Lewis diagrams to show formation of ions and bonding in molecules and compounds.
- d) Investigate the relationship between bond types, resulting structures, and physical properties (solubility, conductivity, melting/boiling points).
- e) Relate bond types and resultant structures to the uses of substances in daily life.
- f) Appreciate the significance of chemical bonding in explaining properties and uses of substances.
1. What are valence electrons? (Octet / Duplet rule)
Valence electrons are the electrons in the outermost shell of an atom. They determine how an atom bonds with other atoms. Many atoms are most stable when they have a full outer shell:
- Octet rule: atoms (especially C, N, O, F and the noble gases) tend to have 8 electrons in the outer shell (like neon, argon).
- Duplet rule: hydrogen and helium are stable with 2 electrons in their outer shell (like helium).
Atoms achieve stable electronic arrangements by losing, gaining or sharing electrons — forming ions or molecules.
2. Types of chemical bonds — simple explanations and school examples
Formed when one atom donates electrons to another, creating positive and negative ions that attract each other. Example: sodium chloride (table salt).
Na+ Cl− → NaCl (ionic lattice)
Formed when atoms share pairs of electrons. Example: O2 (oxygen gas), H2O (water), Cl2 (chlorine gas).
O :: O (double bond in O2; each O shares 2 pairs to achieve octet)
A type of covalent bond where one atom supplies both electrons in the shared pair. Example: formation of ammonium ion from ammonia and a proton.
A weak attraction between a hydrogen atom bonded to a highly electronegative atom (O, N or F) and a lone pair on another electronegative atom. Important in water, DNA, proteins.
Very weak attractions arising from temporary dipoles in molecules. Important in nonpolar molecules like oils and for molecular packing in solids.
In metals, positive ions sit in a 'sea' of delocalized electrons. This explains conductivity, malleability and ductility. Example: copper used in wires.
3. Lewis (electron dot) diagrams — how to draw and examples
Rules: show only valence electrons as dots around element symbols. Shared pairs shown as dots or lines. Brackets and charge show ions.
Na· → Na⁺ [Cl· ·· ··] → [Cl: ]⁻Na loses 1 e−; Cl gains 1 e−. Show charges on ions.
H:O: H
(O has 2 lone pairs shown as pairs of dots)
O shares 1 pair with each H to complete oxygen's octet.
H
|
H—N→H (N donates lone pair to H+)
|
H
Overall charge: +1
Show arrow from N to H+ or show shared pair with bracket and + charge.
4. Bond types → Structures → Physical properties (quick guide)
- Structure: giant ionic lattice
- Melting/boiling: high
- Conductivity: solid = no; molten/aqueous = yes
- Solubility: often soluble in water
- Structure: small molecules (e.g., H2O, CO2)
- Melting/boiling: low (gases or liquids)
- Conductivity: poor
- Solubility: polar covalent (like water) soluble; nonpolar (like oil) not soluble
- Structure: giant lattice with delocalized electrons
- Melting/boiling: usually high
- Conductivity: good (electricity & heat)
- Properties: malleable, ductile, lustrous
5. Uses in daily life (Kenyan examples)
- Table salt (NaCl) — ionic compound used in cooking and food preservation; dissolves in water and conducts when dissolved.
- Copper wires — metallic bonding gives good conductivity; used in household wiring and electronics.
- Water (H2O) — hydrogen bonding causes high boiling point and surface tension; important for life, cooking, cleaning.
- Cooking oils and grease — nonpolar (van der Waals forces) so do not mix with water; detergents have polar and nonpolar parts to remove oil.
- Ammonia-based fertilisers — ionic or ammonium salts (NH4+) supply nitrogen to crops.
- Polymers (plastics) — covalent bonds in long chains; properties depend on bonding and intermolecular forces (e.g., polyethylene bags).
6. Simple classroom practicals & suggested learning experiences
- Test conductivity: compare salt water, sugar water and distilled water using a simple circuit (battery, bulb, wires). Observe which conducts electricity.
- Melting point comparison: heat samples of candle wax (covalent) and a small ionic solid (e.g., salt) to compare behaviour (use safe heating methods and teacher supervision).
- Solubility test: put small amounts of salt, sugar and cooking oil in water to see which dissolve. Discuss polarity and bond type.
- Model building: use beads and sticks to represent ions, covalent bonds and metal lattices to show structures.
- Hydrogen bonding demo: compare evaporation rates of warm water and alcohol (explain role of hydrogen bonding in water retention).
Safety note: always follow teacher instructions and safety rules when doing practicals (goggles, gloves, no direct tasting, safe heating).
7. Short assessment questions (for learners)
- Explain in your own words why sodium forms Na+ and chlorine forms Cl− when they make salt.
- Draw Lewis diagrams for H2, O2 and H2O.
- How does the type of bonding explain why metals conduct electricity while ionic solids conduct only when molten?
- Name a substance used at home that relies on hydrogen bonding and explain one property caused by that bonding.
- Give one example of a dative covalent bond from everyday chemistry and describe how it forms.
Valence electrons determine how atoms join together. Ionic, covalent, dative, hydrogen, van der Waals and metallic bonding explain the structure and properties of substances — such as solubility, melting points and conductivity — and therefore their uses in daily life. Understanding bonding helps explain why materials behave the way they do and how we can use them safely and effectively.