Covalent bondingIB MYP Chemistry: Subtopic test

1. 1
   A biogas plant in Kerala produces methane, CH₄, from rotting plant waste. The methane is burned for cooking. Carbon atoms have four electrons in their outer shell and hydrogen atoms have one.

   (a)

   What type of bonding holds the atoms together in a molecule of methane?

   [1 mark]

   • AIonic bonding, in which electrons are transferred
   • BMetallic bonding, in which electrons are delocalised
   • CWeak forces between the atoms, with no electrons shared
   • DCovalent bonding, in which pairs of electrons are shared

   (b)

   How many pairs of electrons are shared in one molecule of methane?

   [1 mark]

   • ATwo
   • BFour
   • CEight
   • DFive

   (c)

   Describe how a covalent bond forms between a carbon atom and a hydrogen atom.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A scientist studying greenhouse gases examines carbon dioxide, CO₂, which forms when fossil fuels burn. Carbon atoms have four electrons in their outer shell and oxygen atoms have six.

   (a)

   What type of bond joins the carbon atom to each oxygen atom in a molecule of carbon dioxide?

   [1 mark]

   • AA single covalent bond
   • BA triple covalent bond
   • CA double covalent bond
   • DAn ionic bond

   (b)

   How many electrons are shared in total in one molecule of carbon dioxide?

   [1 mark]

   • AEight
   • BFour
   • CSix
   • DSixteen

   (c)

   Explain how the atoms in a molecule of carbon dioxide each end up with a full outer shell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student uses a molecular model kit to compare molecules of methane (CH₄), ammonia (NH₃) and water (H₂O). Carbon atoms have four outer electrons, nitrogen atoms five and oxygen atoms six. She records how many hydrogen atoms attach to the central atom of each molecule.

   (a)

   Describe the pattern in her results and use it to predict the number of hydrogen atoms that attach to a fluorine atom, which has seven outer electrons.

   [3 marks]

   (b)

   Explain why the atoms bond in this pattern, and evaluate the use of a model kit to show covalent bonds.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Nitrogen gas, N₂, makes up about 78% of the air. A fertiliser company in Brazil reacts nitrogen from the air with hydrogen to make ammonia, NH₃, which farmers spread on their fields as a fertiliser.

   (a)

   Describe single, double and triple covalent bonds, using chlorine, Cl₂, carbon dioxide, CO₂, and nitrogen, N₂, as examples.

   [6 marks]

   (b)

   Discuss the social, economic and environmental implications of using ammonia-based fertilisers, and evaluate whether farmers should use them.

   [6 marks]

   Total for question 4: 12 marks

End of questions