1. 1
   A student fills a balloon with helium gas and leaves it in a sealed classroom for several weeks alongside samples of oxygen, chlorine and nitrogen. At the end of the investigation, the helium has not reacted with any other gas in the room, while some of the other gases have formed new compounds with each other.

   (a)

   Which electronic configuration correctly explains why helium is so unreactive?

   [1 mark]

   • AHelium has a full outer shell of 2 electrons, giving it a stable electron arrangement
   • BHelium has 1 electron in its outer shell, so it readily forms metallic bonds
   • CHelium has 7 electrons in its outer shell and easily gains one more
   • DHelium has no electrons in its outer shell, so it cannot form bonds of any kind

   (b)

   Helium, neon and argon are all found in the same vertical column of the periodic table. What is this column called, and what property do all its members share?

   [1 mark]

   • APeriod 0; they all have the same number of electron shells
   • BGroup 7 (the halogens); they all have 7 outer electrons
   • CGroup 0 (the noble gases); they all have full outer electron shells
   • DGroup 1 (the alkali metals); they all react vigorously with water

   (c)

   Using ideas about electronic configuration, explain why the helium in the student's balloon did not react with any of the other gases over the several weeks of the investigation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineering company uses argon gas to surround the hot metal joint during arc welding, and separately fills large airships with helium instead of hydrogen.

   (a)

   Why is argon chosen to surround the weld during welding?

   [1 mark]

   • AArgon is flammable and helps sustain the welding flame
   • BArgon is highly reactive and bonds with the metal to strengthen the weld
   • CArgon is denser than air, so it cools the metal joint more quickly
   • DArgon is inert, so it prevents the hot metal from reacting with oxygen in the air

   (b)

   Historically, some airships used hydrogen gas for lift, but modern airships use helium instead. Which pair of properties best explains why helium is the safer choice?

   [1 mark]

   • AHelium has a high density and is highly reactive
   • BHelium has a low density and is non-flammable
   • CHelium is flammable but has a very low density
   • DHelium is more expensive but reacts with oxygen to form a protective layer

   (c)

   Explain two properties of helium that make it a suitable and safe gas for filling airships.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician records the boiling points of four Group 0 elements: helium boils at -269°C, neon at -246°C, argon at -186°C and krypton at -153°C.

   (a)

   Describe the pattern in boiling point shown by these values as the group is descended, and use this pattern to predict, in general terms, how the boiling point of xenon (which lies below krypton in Group 0) would compare with that of krypton.

   [3 marks]

   (b)

   The technician also finds that the density of the noble gases increases going down Group 0, from helium (the least dense) to krypton (denser than argon, neon and helium). Describe this pattern in density, explain why it occurs, and use it to predict how the density of radon (which lies below krypton in Group 0) would compare with the density of krypton.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A lighting company manufactures two products: incandescent filament light bulbs, which are filled with argon gas around a hot metal filament, and advertising signs, which are filled with neon gas that glows red when an electric current passes through it.

   (a)

   Explain why argon is a suitable gas to fill a light bulb around a hot metal filament, referring to its chemical properties and the conditions inside a working bulb.

   [6 marks]

   (b)

   Argon (used in light bulbs) and neon (used in glowing signs) both belong to Group 0, yet they have different physical properties such as boiling point and density. Explain, in terms of electronic configuration, why all Group 0 elements share similar chemical behaviour despite these differences in physical properties.

   [6 marks]

   Total for question 4: 12 marks

End of questions