1. 1
   A student is investigating the bonding in hydrogen chloride, HCl. A single molecule of hydrogen forms when two hydrogen atoms join together, and a single molecule of hydrogen chloride forms when a hydrogen atom joins with a chlorine atom.

   (a)

   Which statement correctly describes how the covalent bond in hydrogen chloride forms?

   [1 mark]

   • AA pair of electrons, one from the hydrogen atom and one from the chlorine atom, is shared between the two atoms
   • BAn electron is transferred completely from the hydrogen atom to the chlorine atom
   • CAn electron is transferred completely from the chlorine atom to the hydrogen atom
   • DThe nuclei of the two atoms merge to form a single larger nucleus

   (b)

   Which type of particle is formed when covalent bonding occurs between atoms, as in the hydrogen chloride example?

   [1 mark]

   • AAn isotope
   • BAn ion
   • CA lattice
   • DA molecule

   (c)

   Describe fully, in words, how the covalent bond forms between the hydrogen atom and the chlorine atom in a molecule of hydrogen chloride.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A teacher compares two substances: sodium chloride, which is made of ions held together by strong electrostatic forces, and methane, CH4, which is a simple molecular substance held together by covalent bonds within each molecule.

   (a)

   Which statement about methane is correct?

   [1 mark]

   • AMethane consists of ions held together by electrostatic forces of attraction
   • BMethane consists of molecules in which the carbon atom shares one pair of electrons with each of four hydrogen atoms
   • CMethane consists of a giant lattice of carbon and hydrogen atoms
   • DMethane consists of a single shared pair of electrons between one carbon atom and one hydrogen atom

   (b)

   Which statement correctly compares the size of a methane molecule with the size of a single carbon atom?

   [1 mark]

   • AA methane molecule is roughly a thousand times smaller than a single carbon atom
   • BA methane molecule is roughly a million times larger than a single carbon atom
   • CA methane molecule is of a similar order of magnitude in size to a single atom, since atoms and small molecules are both extremely small
   • DA methane molecule has no definite size, unlike a single atom

   (c)

   Explain, in terms of electrons, how methane forms as a simple molecular covalent substance, and state how many covalent bonds are present in one molecule of methane.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is asked to describe the bonding in a molecule of water, H2O.

   (a)

   Explain fully, in words, how the covalent bonds in a water molecule are formed, referring to the outer-shell electrons of the oxygen and hydrogen atoms.

   [3 marks]

   (b)

   Carbon dioxide, CO2, is another simple molecular substance formed by covalent bonding. Each carbon atom shares two pairs of electrons with each oxygen atom, forming a double covalent bond on each side. Explain how this differs from the bonding in a water molecule, and state the total number of shared pairs of electrons in one molecule of carbon dioxide.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A group of students is given four labelled substances to investigate: hydrogen gas, hydrogen chloride gas, oxygen gas and methane gas. They are told that all four are simple molecular, covalent substances.

   (a)

   Explain how covalent bonding accounts for the formation of molecules in these substances, describing how the number of electrons an atom needs to complete its outer shell determines how many covalent bonds it forms, and use hydrogen, oxygen and methane as your examples.

   [6 marks]

   (b)

   One student in the group suggests that hydrogen chloride gas must be an ionic compound because it contains a metal-like element combined with a non-metal. Using your understanding of covalent bonding, explain why this suggestion is incorrect, describing how hydrogen chloride actually forms and how its bonding differs from that of an ionic compound such as sodium chloride.

   [6 marks]

   Total for question 4: 12 marks

End of questions