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The Covalent Model · Paper 2 — Free Chemistry SL Practice Questions

What this topic covers

Every property question IB throws at you — why does this melt higher, why does that conduct here but not there — traces back to one of three bonding models: ionic, covalent, or metallic. This topic asks you to build each model from its electrostatic basics, then use it to predict and explain real behaviour: melting point, conductivity in different states, shape, solubility, malleability. The exam almost never tests the model in isolation — it tests whether you can name the right structural detail (coordination number, electron domain count, number of delocalized electrons) and explain why that detail produces the observed property. Vocabulary without mechanism gets you nowhere on the mark scheme.

Read the full Structure: Models of Bonding and Structure lesson notes →

1MasterySAQ-SPolar vs non-polar covalent bonds5 marksPaper 2~8 min

A student investigates the solubility of tetrachloromethane (

\text{CCl}_4

) and trichloromethane (

\text{CHCl}_3

) in water. The student predicts that

\text{CCl}_4

will be insoluble in water, while

\text{CHCl}_3

will show some solubility. Electronegativity values:

\chi(\text{H}) = 2.20

\chi(\text{C}) = 2.55

\chi(\text{Cl}) = 3.16

\chi(\text{O}) = 3.44

(a)

State why the

\text{C{-}Cl}

bond is polar, and explain why the

\text{CCl}_4

molecule has no net dipole moment. [2 marks]

(b)

Deduce why

\text{CHCl}_3

has a net dipole moment, whereas

\text{CCl}_4

does not. [2 marks]

(c)

Explain why

\text{CHCl}_3

shows greater solubility in water than

\text{CCl}_4

. [1 mark]

Solutions

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