Electronegativity and bond polarityEdexcel A-Level Chemistry: Subtopic test

1. 1
   A chemist compares the hydrogen halides. The Pauling electronegativity values are: H 2.1, F 4.0, Cl 3.0, Br 2.8 and I 2.5.

   (a)

   Which of these bonds is the most polar?

   [1 mark]

   • AH–Cl
   • BH–Br
   • CH–F
   • DH–I

   (b)

   Which row correctly shows the partial charges on a hydrogen chloride molecule?

   [1 mark]

   • AHδ⁻–Clδ⁺
   • BHδ⁺–Clδ⁻
   • CH⁺–Cl⁻ with a full charge on each atom
   • DNo charges, because the electrons are shared equally

   (c)

   Explain why the bond in hydrogen fluoride is polar.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Some Pauling electronegativity values are: Na 0.9, Mg 1.2, Al 1.5 and Cl 3.0. A student compares the bonding in the chlorides NaCl, MgCl₂ and AlCl₃.

   (a)

   Which bond has the greatest ionic character?

   [1 mark]

   • AAl–Cl
   • BNa–Cl
   • CMg–Cl
   • DThey are all equally ionic

   (b)

   What is the electronegativity difference between sodium and chlorine?

   [1 mark]

   • A2.1
   • B1.8
   • C1.5
   • D3.9

   (c)

   Explain what is meant by saying that ionic and covalent bonding are the extremes of a continuum, using the bonding in aluminium chloride as an example.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A teacher brings a charged plastic rod close to a thin stream of liquid running from a burette. The streams of water and trichloromethane, CHCl₃, are deflected towards the rod. The streams of tetrachloromethane, CCl₄, and hexane are not deflected. The Pauling electronegativity values are: H 2.1, C 2.5 and Cl 3.0.

   (a)

   Explain why tetrachloromethane is not deflected even though it contains polar bonds.

   [3 marks]

   (b)

   Explain why trichloromethane is deflected. Boron trifluoride, BF₃, is a planar molecule with bond angles of 120°. Predict, with a reason, whether it is polar.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Pauling electronegativity values are: H 2.1, C 2.5, O 3.5, Na 0.9 and Cl 3.0. A student compares the bonding in several substances: water and carbon dioxide (both contain oxygen), and chlorine, methane, hydrogen chloride and sodium chloride.

   (a)

   Explain why water is a polar molecule but carbon dioxide is a non-polar molecule, even though both contain polar bonds.

   [6 marks]

   (b)

   Use the electronegativity values to explain how the bonding in chlorine, methane, hydrogen chloride and sodium chloride illustrates a continuum between covalent and ionic bonding.

   [6 marks]

   Total for question 4: 12 marks

End of questions