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IB Chemistry HL 2.2 The Covalent Model Questions

Practise IB Chemistry HL 2.2 with evidence-led questions on bonding models, molecular geometry, polarity and structure.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Construct and interpret Lewis structures, including formal charge, resonance contributors and expanded octets.
  • Use VSEPR, electron domains and hybridization to predict molecular geometry, bond angles and sigma/pi bonding.
  • Determine bond polarity and molecular polarity from electronegativity and three-dimensional symmetry.
  • Explain covalent-network properties and bond-strength trends using bond order, bond length and lattice structure.
  • Identify intermolecular forces and use them to explain phase changes, solubility and material properties.

Covered syllabus points

2.2.1—Covalent bonding2.2.2—Bond types and strength2.2.3—Coordination bonds2.2.4—VSEPR model2.2.5—Bond polarity2.2.6—Molecular polarity2.2.7—Covalent network structures2.2.8—Intermolecular forces (IMF)2.2.9—IMF strength and properties2.2.10—Chromatography2.2.11 (HL)—Resonance structures2.2.12 (HL)—Benzene (C₆H₆)2.2.13 (HL)—Expanded octets2.2.14 (HL)—Formal charge2.2.15 (HL)—Sigma (σ) and pi (π) bonds2.2.16 (HL)—Hybridization

Learn this topic

Study 2.2 The covalent model conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

Question 1

[Maximum number: 4]

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula PH3\mathrm{PH}_{3}.

Question (a)

(a)

Draw a Lewis (electron dot) structure of phosphine.

[ 1 ]

Question (b)

(b)

State the hybridization of the phosphorus atom in phosphine.

[ 1 ]

Question (c)

(c)

Outline whether you expect the bonds in phosphine to be polar or non-polar, giving a brief reason.

Figure for Question (c) — IB Chemistry HL

Phosphine has a much greater molar mass than ammonia. Explain why phosphine has a significantly lower boiling point than ammonia.

[ 2 ]

Question 2

[Maximum number: 12]

Question (a)

(a)

An organic compound, X, with a molar mass of approximately 88 g mol−188 \mathrm{~g} \mathrm{~mol}^{-1} contains 54.5 % carbon, 36.3 % oxygen and 9.2 % hydrogen by mass.

[ 5 ]

Question (i)

(i)

The carboxylic acid contains two different carbon-oxygen bonds. Identify which bond is stronger and which bond is longer.

Stronger bond:

Longer bond:

[ 2 ]

Question (ii)

(ii)

Predict and explain the bond lengths and bond strengths of the carbon-oxygen bonds in CH3CH2COO−\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COO}^{-}.

[ 3 ]

Question (b)

(b)

State the meaning of the term hybridization.

[ 1 ]

Question (c)

(c)

Describe the hybridization of the carbon atom in methane and explain how the concept of hybridization can be used to explain the shape of the methane molecule.

[ 3 ]

Question (d)

(d)

Identify the hybridization of the carbon atoms in diamond and graphite and explain why graphite is an electrical conductor.

[ 3 ]

Question 3

[Maximum number: 2]

Solid ionic compounds form crystal lattices.

Cobalt also forms chlorides with the formula CoCl2\mathrm{CoCl}_{2}.

Hydrated cobalt (II) ions, Co(H2O)62+\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{ }^{2+}, are pink. Describe the interaction between the cobalt ion and a water molecule in terms of the type of bond and how this bond is formed.

Type of bond:
How the bond forms:
CoCl42−\mathrm{CoCl}_{4}{ }^{2-} ions are blue.

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