Group 7 (Halogens): Answers

 Describe the appearance of the halogens as you go down the group.

As you go down the group, the elements get darker in colour. Fluorine is right at the top of the group and is pale yellow, chlorine is green, bromine is an orange-brown colour, iodine is greyish and astatine is black.

Which of the halogens is a poisonous green gas?

Chlorine is a poisonous green gas. It’s so deadly that it was used as a chemical weapon during World War I. However, in the quantities used to clean swimming pools and to disinfect drinking water are so small that it isn’t enough to cause any harm.

How does the reactivity of the group 7 elements change as you go down the group?

The reactivity of the halogens decreases as you go down the group.

Explain the trend in reactivity of the group 7 elements.

As you go down the group, the distance between the nucleus and the outer electron increases. This reduces the electrostatic attraction and makes it more difficult for the element to gain an extra electron to achieve a full outer shell.

Write an equation for the displacement reaction between chlorine and potassium iodide.

What would you observe when the following substances are mixed together?

• Bromine and lithium iodide?

Bromine is more reactive than iodine, so it will displace it and form lithium bromide. The other product is iodine. Since bromine is an orange-brown colour in solution and iodine is colourless, we will see our solution turn from orange to colourless.

• Fluorine and sodium bromide?

Fluorine is more reactive than bromine so it will replace it to form sodium fluoride and bromine. Fluorine is colourless and bromine is orange-brown so we will see a change from a colourless to brown solution.

• Iodine and sodium chloride?

Iodine is less reactive than chlorine so there will be no reaction.