Astatine is a halogen found below iodine in Group 7. Predict and explain the properties of astatine compared to iodine, including its reactivity and physical state at room temperature.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Astatine is a very rare halogen at the bottom of Group 7. It is a radioactive element that is difficult to study, so scientists use trends in Group 7 to predict its properties.
Model answer (4 marks)
Astatine is less reactive than iodine because it has more electron shells; the outer shell is further from the nucleus, making it harder for astatine to gain an electron. Consequently, astatine has a higher boiling point than iodine and is a solid at room temperature, as boiling points increase down Group 7.
Examiner tips
- State the trend in reactivity and explain it with electron shell distance.
- Mention the higher boiling point and solid state, linking to the down‑group trend.
Common mistakes
- Claiming astatine is more reactive than iodine.
- Saying astatine is a gas or liquid at room temperature.
- Ignoring the electron shell explanation for reactivity.
Mark scheme (4 marks)
- Astatine is less reactive than iodine
- Because astatine has more electron shells / the outer shell is further from the nucleus, so it is harder / less able to gain an electron
- Astatine has a higher boiling point than iodine / is a solid at room temperature
- Because boiling points increase down Group 7 / the trend in Group 7 is increasing boiling point going down the group
Key terms in this question
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Predict and explain" question →
- Decode the mark scheme abbreviations →