IB Chemistry HL S2.2 The covalent model questions

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Question 1

Multiple choiceEasy1 mark

Four molecules are compared to assess how bond polarity and molecular geometry affect molecular polarity. Which molecule has a net dipole moment?

Show answer and explanation

Answer: A. A molecule has a net dipole when its bond dipoles do not cancel. H $_2$ O is bent, so its two O–H bond dipoles do not cancel.

B: Treats polar C=O bonds as sufficient for molecular polarity, overlooking cancellation in linear CO $_2$ C: Treats polar B–F bonds as sufficient, overlooking cancellation in trigonal-planar BF $_3$ D: Treats polar C–Cl bonds as sufficient, overlooking cancellation in tetrahedral CCl $_4$

Remember: molecular polarity depends on both bond polarity and geometry.

Question 2

Paper 2Medium6 marks

Figure 1 shows reference bond angles for methane, ammonia and water. Each central atom has four electron domains.

(a)

Use Figure 1 to state the bond angle in water and compare the bond angles in ammonia and water.

[2]

(b)

Explain the difference between the bond angles in ammonia and water in terms of the electron domains around their central atoms.

[2]

(c)

Ammonia reacts with a hydrogen ion to form an ammonium ion:

\ce{NH3 + H+ -> NH4+}

Identify the atom that donates the electron pair to $\ce{H+}$ and explain why the N–H bond formed is a coordination bond.

[2]

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