Explaining the trend in the reactivity of the halogens
2 marks · EasyThe table below gives the melting points of chlorine and bromine (both Group 7 elements):
| Element | Melting point (°C) |
|---|---|
| Chlorine | -101 |
| Bromine | -7 |
Iodine is the next element down the group after bromine. Use the data to estimate a likely melting point for iodine and explain your reasoning based on group trends.
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Iodine's melting point is likely to be higher than bromine's, e.g., near 114 °C (any reasonable value above -7 °C with explanation based on increasing melting points down the group accepted). °C
Also accept: Any value above -7 °C, with explanation that melting point increases down the group
Common mistakes: Giving a value between Cl and Br; Decreasing melting point
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Marking points
M1 · 1 mark · Identifies the trend that melting point increases down Group 7.
A1 · 1 mark · Gives a reasonable estimated melting point for iodine above -7 °C (e.g., 100–120 °C). (follow-through)
Worked solution
Going down Group 7, the melting point increases. Chlorine melts at -101 °C, bromine at -7 °C; iodine's melting point is above -7 °C.
Estimated melting point for iodine: a value higher than -7 °C, for example, around 114 °C.