1.4.10Physical Chemistry
Effects of Structure and Bonding — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 26 of 102
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Four Structure Types
Giant ionic
- Giant ionic Oppositely charged ions in a lattice give high melting points, brittleness, and conduction only when molten or dissolved.
Giant metallic
- Giant metallic Positive ions in a sea of electrons give good conduction in all states, malleability and generally high melting points.
Giant covalent
- Giant covalent A network of covalent bonds gives very high melting points, great hardness and poor conductivity, with graphite as the exception.
Simple molecular
- Simple molecular Discrete molecules with weak intermolecular forces give low melting points, poor conductivity and softness.
| Type | Melting point | Conducts when solid? | Conducts when liquid? |
|---|---|---|---|
| Ionic | High | No | Yes |
| Metallic | Usually high | Yes | Yes |
| Giant covalent | Very high | No (graphite yes) | No |
| Simple molecular | Low | No | No |
Part 2 of 4Deducing a Structure
1
First look at electrical conductivity in the solid state, because only metals and graphite conduct when solid.
2
If the solid does not conduct, check whether the molten or dissolved state conducts, which would indicate an ionic compound.
3
If no state conducts, decide between simple molecular and giant covalent using the melting point.
4
A low melting point and softness point to simple molecular, whereas a very high melting point and hardness suggest giant covalent.
5
Support the conclusion by naming the particles and the forces or bonds that must be overcome.
Part 3 of 4Comparing Trends
Comparing Trends
Ionic strength
- Ionic strength Melting points rise with greater ionic charge and smaller ionic radius, so MgO melts higher than NaCl.
Metallic strength
- Metallic strength Strength rises with more delocalised electrons and higher ion charge, so aluminium bonds more strongly than sodium.
Molecular size
- Molecular size Larger molecules have stronger intermolecular forces, giving higher melting points even though covalent bonds are unchanged.
Hardness
- Hardness Giant covalent and ionic solids are hard, while metals bend and simple molecular solids are soft.
Part 4 of 4Exam Checklist & Tips
1.4.10 – Key Points for the Exam
- Structure The arrangement of particles in a substance, such as a giant lattice or separate molecules.
- Bonding The type of attraction holding the particles together.
- Giant lattice A very large three-dimensional array of particles joined by bonds in all directions.
- Intermolecular force A weak attraction between neighbouring molecules.
Common Mistakes
- Naming the wrong particle when explaining conduction, such as electrons in an ionic liquid.
- Using the phrase "breaking bonds" for simple molecular substances when only intermolecular forces are overcome.
- Assuming every solid with a high melting point is ionic and overlooking giant covalent and metallic lattices.
- Not saying which state is being considered when asked about conductivity.
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