Year 8 Science · Unit 2 · Lesson 16
Apply Worksheet
Learning Goals
1. Write the comparison frame the lesson recommends, and say what each half of it shows.
Match each question to the most useful feature
Write the matching letter in the middle column. Each letter is used once.
| Question | Letter | Most useful feature |
|---|---|---|
| Do magnesium and barium behave in a similar way? | A. Atomic number | |
| Which conducts electricity: aluminium or sulfur? | B. Period number | |
| How many protons are in a bromine atom? | C. Which element is higher in its group | |
| Which is more reactive, chlorine or iodine? | D. Category (metal, metalloid or non-metal) | |
| Which atom has more electron shells, sodium or bromine? | E. Whether they are in the same group |
Read the data
| Element | Atomic number | Period | State at 25 °C | Colour | Boiling point (°C) |
|---|---|---|---|---|---|
| Fluorine (F) | 9 | 2 | Gas | Pale yellow | −188 |
| Chlorine (Cl) | 17 | 3 | Gas | Yellow-green | −34 |
| Bromine (Br) | 35 | 4 | Liquid | Red-brown | 59 |
| Iodine (I) | 53 | 5 | Solid | Grey-black | 184 |
Source: published values for the halogens; each boiling point is given to the nearest whole degree.
2. Describe how the boiling point changes going down Group 17. Astatine (At) sits below iodine: predict its state at 25 °C and give your reason.
Classify with a reason
Four students compared chlorine and iodine. Write “strong” (relevant evidence, correct), “weak” (true but shallow) or “wrong” (uses evidence that does not support the claim), and give a reason.
| Sentence | Verdict | Reason |
|---|---|---|
| a. “Chlorine and iodine are both elements.” | ||
| b. “Iodine is more reactive because it has more protons (53) than chlorine (17).” | ||
| c. “Both are Group 17 non-metals, but chlorine is higher in the group, so it is more reactive.” | ||
| d. “Both are halogens, but chlorine is a gas at 25 °C while iodine, with a boiling point of 184 °C, is a solid.” |
Scenario: the science cupboard
A school science cupboard holds a jar of iodine crystals, and students use iodine solution in class. The school never keeps fluorine: it is far too dangerous to handle outside a specialist laboratory.
3. Compare fluorine and iodine to explain why one is kept in the school and the other is not. Use at least three features from Table 1 or the periodic table, and say which feature best explains the difference in safety.
1. “Both … but …”. The “both” half gives a similarity; the “but” half gives a difference. [2 marks: 1 frame, 1 what each half shows]
Match each question to the most useful feature
Do magnesium and barium behave in a similar way? → E; Which conducts electricity: aluminium or sulfur? → D; How many protons are in a bromine atom? → A; Which is more reactive, chlorine or iodine? → C; Which atom has more electron shells, sodium or bromine? → B.
Read the data
2. Boiling point increases going down the group (from −188 °C for fluorine to 184 °C for iodine). Astatine: a solid, because the states change from gas to liquid to solid going down and its boiling point should be higher than iodine’s. [3 marks: 1 pattern, 1 solid, 1 reason]
Classify with a reason
a: weak; true, but it gives no feature and would fit any two elements. b: wrong; atomic number does not explain reactivity here, and iodine is less reactive because reactivity decreases down Group 17. c: strong; uses group and position in the group, which is the relevant feature for reactivity. d: strong; uses group, state and boiling point, which are relevant evidence for comparing states.
Show What You Know
3. Marking guide (points expected): 1 similarity: both are Group 17 non-metals (halogens); 1 differences from the table: fluorine is a pale yellow gas in Period 2 (atomic number 9), iodine is a grey-black solid in Period 5 (atomic number 53); 1 position in the group is the feature that best explains reactivity; 1 fluorine is at the top of Group 17 and reactivity decreases going down, so fluorine is far more reactive than iodine; 1 link: fluorine reacts violently with almost anything, so it is too dangerous for a school, while iodine reacts gently enough to handle with care. [5 marks]
Common error to watch for: using the Group 1 rule (“lower in the group means more reactive”) for the halogens, or using atomic number as the reason for reactivity. Group 17 reactivity decreases going down.