IGCSE Chemistry Paper 4
Topic 2.5.1: Covalent Bonding I
Drawing Simple Molecules • Dot-and-Cross Diagrams • Core Content
⚠️Instructions
- •Answer ALL questions. This exam tests Core content only.
- •Total marks available: 50 marks
- •For drawing questions, show all outer shell electrons using dots and crosses
- •Use the "Reveal Answer" button to check your responses and see the mark scheme
Section A: Definitions & Key Terms (15 marks)
Question 1
[3 marks]Define a covalent bond.
Question 2
[2 marks]State what is meant by a simple molecular compound.
Question 3
[3 marks]Explain why atoms form covalent bonds instead of remaining as separate atoms.
Question 4
[2 marks]In a dot-and-cross diagram, what do the dots and crosses represent?
Question 5
[2 marks]How many electrons are in the outer shell of a hydrogen atom? How many does it need to achieve a stable configuration?
Question 6
[3 marks]State the molecular formulae for:
- (a) Water
- (b) Ammonia
- (c) Methane
Section B: Drawing Dot-and-Cross Diagrams (25 marks)
Question 7
[5 marks][DRAWING REQUIRED] Draw a dot-and-cross diagram for a molecule of water (H₂O).
Show all electrons in the outer shells only. You do not need to show inner shells.
Question 8
[5 marks][DRAWING REQUIRED] Draw a dot-and-cross diagram for a molecule of ammonia (NH₃).
Show all electrons in the outer shells only.
Question 9
[5 marks][DRAWING REQUIRED] Draw a dot-and-cross diagram for a molecule of methane (CH₄).
Show all electrons in the outer shells only.
Question 10
[3 marks][DRAWING REQUIRED] Draw a dot-and-cross diagram for a molecule of hydrogen (H₂).
Question 11
[4 marks][DRAWING REQUIRED] Draw a dot-and-cross diagram for a molecule of chlorine (Cl₂).
Show all electrons in the outer shells only. (Chlorine has 7 outer electrons.)
Question 12
[3 marks][DRAWING REQUIRED] Draw a dot-and-cross diagram for a molecule of hydrogen chloride (HCl).
Section C: Identification & Application (10 marks)
Question 13
[2 marks]Which of the following substances contain covalent bonds?
NaCl, Mg, CH₄, CaCl₂, H₂O, Fe
Question 14
[4 marks]A student draws the following dot-and-cross diagram for ammonia:
(a) Identify TWO mistakes in this diagram. [2 marks]
(b) Explain why these mistakes are incorrect. [2 marks]
Question 15
[4 marks]Complete the following table showing the number of covalent bonds formed by different atoms:
| Element | Group Number | Outer Electrons | Number of Covalent Bonds |
|---|---|---|---|
| Hydrogen | 1 | 1 | ? |
| Carbon | ? | 4 | 4 |
| Nitrogen | 5 | ? | 3 |
| Oxygen | 6 | 6 | ? |
📊 Exam Summary
🎯 Key Topics Covered:
- ✓ Covalent bond definition and formation
- ✓ Dot-and-cross diagrams for H₂, Cl₂, H₂O, NH₃, CH₄, HCl
- ✓ Understanding lone pairs vs bonding pairs
- ✓ Noble gas configurations
- ✓ Identifying covalent compounds
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