Year 9 Science · Unit 2 · Lesson 06
Challenge Worksheet
Learning Goals
1. For the first 20 elements, state the maximum number of electrons in shells 1, 2 and 3. Then write the electron configuration of phosphorus (atomic number 15).
Find the error
A student wrote these six electron configurations. Tick the correct ones. Correct each wrong one in the last column.
| Element (atomic number) | Student’s answer | Correct? (✓ or ✗) | Correction |
|---|---|---|---|
| Aluminium (13) | 2,8,3 | ||
| Potassium (19) | 2,8,9 | ||
| Oxygen (8) | 2,6 | ||
| Silicon (14) | 2,4,8 | ||
| Magnesium (12) | 2,10 | ||
| Calcium (20) | 2,8,8,2 |
2. The student’s three errors each break a filling rule. State the rule broken in each case.
3. A student claims: “All atoms want 8 electrons in their outer shell. That is the only way to become stable.” Identify two problems with this claim, using named elements as evidence.
Scenario: which halogen wins?
A more reactive halogen takes the place of a less reactive one in a compound. For example, chlorine takes bromine’s place in potassium bromide and frees orange bromine. Students added a few drops of each halogen solution to solutions of three potassium compounds and looked for a colour change.
| Halogen added | Potassium chloride | Potassium bromide | Potassium iodide |
|---|---|---|---|
| Chlorine | – | ✓ turned orange | ✓ turned brown |
| Bromine | ✗ | – | ✓ turned brown |
| Iodine | ✗ | ✗ | – |
Source: sample class results. Fluorine is too dangerous to use in a school laboratory.
4. Use Table 1 to rank chlorine, bromine and iodine from most to least reactive. Quote the evidence for the top and bottom of your ranking.
5. Fluorine is 2,7 and chlorine is 2,8,7. Both need one electron. Suggest why fluorine grabs that electron more strongly. Use the idea of distance from the nucleus.
6. In Group 1, potassium (four shells) is more reactive than sodium (three shells). A student concludes: “More shells always means more reactive.” Use Table 1 to evaluate this conclusion, and explain why adding shells has opposite effects in Group 1 and Group 17.
7. A textbook states: “Noble gases never react, because their outer shells are full.” In 1962 chemists made xenon difluoride (XeF₂), a compound of the noble gas xenon. Under ordinary conditions, no compound of helium, neon or argon is known. Evaluate the textbook statement.