Topic 2.5.2: Complex Covalent Diagrams
Paper 4 Focus: Advanced Drawing & Molecular Structure
📋 Paper 4 Skills Tested:
- • Dot-and-cross diagrams with correct electron placement
- • Double and triple bond representation
- • 3D molecular shape drawing (wedge-dash notation)
- • Structural formulas with functional groups
- • Electron counting and lone pair identification
Section A: Electron Counting
Questions 1-5 • 5 marks
How many electrons are shared in a nitrogen molecule (N₂)?
How many bonding pairs and lone pairs are in a water molecule (H₂O)?
In ammonia (NH₃), how many electrons does nitrogen share with the three hydrogen atoms?
How many electrons are in the outer shell of a carbon atom in methane (CH₄)?
Oxygen gas (O₂) has a double bond. State how many pairs of electrons are NOT involved in bonding on each oxygen atom.
Section B: Advanced Drawing
Questions 6-10 • 12 marks • HIGH SKILL REQUIREMENT
[DRAWING REQUIRED] Draw the dot-and-cross diagram for carbon dioxide (CO₂). Show all outer shell electrons.
[DRAWING REQUIRED] Draw the dot-and-cross diagram for ethene (C₂H₄). Show the double bond between carbon atoms.
[DRAWING REQUIRED] Draw the displayed formula (structural formula) for ethanoic acid (CH₃COOH). Show all bonds.
[DRAWING REQUIRED] Draw the dot-and-cross diagram for hydrogen chloride (HCl). Show only outer shell electrons.
[DRAWING REQUIRED] Ammonia (NH₃) has a pyramidal shape. Draw the 3D structure showing the bond angles.
Section C: Methanol Applications
Questions 11-15 • 11 marks • Mixed Skills
[DRAWING REQUIRED] Draw the dot-and-cross diagram for methanol (CH₃OH), showing only the outer shell electrons.
State the molecular formula of methanol.
Explain why methanol dissolves well in water, using ideas about intermolecular forces.
Methanol can be oxidized to form methanal (HCHO) and then methanoic acid (HCOOH). Suggest the oxidizing agent used.
Calculate the percentage by mass of oxygen in methanol (CH₃OH). [Relative atomic masses: C = 12, H = 1, O = 16]
🎯 Paper 4 Success Strategy
Drawing Checklist:
- ✓ Different symbols for different atoms
- ✓ All outer shell electrons shown
- ✓ Correct number of bonds
- ✓ Lone pairs clearly visible
Common Mistakes to Avoid:
- ✗ Forgetting lone pairs on oxygen/nitrogen
- ✗ Using same symbol for all electrons
- ✗ Incorrect bond angles in 3D shapes
- ✗ Missing double bond in C=O groups
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