Explaining the trend in the reactivity of the halogens
2 marks · HardAstatine is the element below iodine in Group 7 of the Periodic Table.
Predict the colour and state of astatine at room temperature. Justify your predictions using group trends.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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Also accept: Astatine is predicted to be a very dark grey or black solid at room temperature. This is because in Group 7, the colour of the elements becomes darker as you go down the group, and the state changes from gases (like fluorine and chlorine) to liquid (bromine) to solid (iodine), so astatine would be an even darker solid.
Common mistakes: Saying astatine is a gas or a pale colour; not linking to group trends.
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Marking points
M1 · 1 mark · States or predicts that astatine is a solid at room temperature, based on group trends.
M2 · 1 mark · Predicts very dark grey or black as astatine's colour, explaining that halogen colours darken down the group.
Worked solution
As you go down Group 7, halogens get darker in colour and go from gases to solids. Fluorine is pale yellow and a gas, chlorine is green and a gas, bromine is red-brown and a liquid, and iodine is dark grey or purple-black and a solid at room temperature.
Therefore, astatine, being below iodine, will be even darker in colour (very dark grey or black) and will be a solid at room temperature.