Year 8 Science · Unit 2 · Lesson 13
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Learning Goals
Match each part of the table to its description
Write the matching letter in the middle column. Each letter is used once.
| Part of the table | Letter | Description |
|---|---|---|
| Group 1 (alkali metals) | A. Reactive non-metals, such as fluorine, chlorine and bromine. | |
| Group 17 (halogens) | B. Metals with two outer electrons, such as magnesium and calcium. | |
| Group 18 (noble gases) | C. Very reactive metals with one outer electron; they fizz or catch fire in water. | |
| Group 2 (alkaline earth metals) | D. A row whose elements all have three electron shells, from sodium to argon. | |
| Period 3 | E. Gases with a full outer shell, found at the far right of the table. |
1. Calcium is in group 2, period 4. State what the group number and the period number each tell you about a calcium atom.
Odd one out
In each row, three of the electron arrangements belong to atoms in the same group or the same period. Circle the odd one out and say what the other three share.
| Row | Electron arrangements | Odd one out, and what the other three share |
|---|---|---|
| 1 | 2,8,3 · 2,8,7 · 2,5 · 2,8,1 | |
| 2 | 2,8,8 · 2,4 · 2,7 · 2,2 | |
| 3 | 2 · 2,8 · 2,8,8 · 2,8,2 |
Scenario: the torn poster
The class periodic table poster was torn down in a storm. Five boxes were found, but each one is missing some information. Remember: the number of shells in an atom’s electron arrangement gives its period.
| Box | Atomic number | Symbol | Group | Period |
|---|---|---|---|---|
| P | 12 | Mg | 3 | |
| Q | 17 | 3 | ||
| R | 19 | K | 1 | |
| S | 10 | 18 | ||
| T | Si | 14 | 3 |
Source: real periodic table data; the torn poster is made up.
2. Complete the empty cells in Table 1. Then show how the electron arrangement of box P proves it belongs in period 3.
3. A student wants to predict how the element in box Q reacts, but no two boxes share a group. Which search strategy should she use on a full periodic table, and name one element she would find? Explain your choice.
4. A sign maker needs a gas to fill a glass tube that lights up. Anything reactive could react with the metal parts inside. The shortlist is neon (group 18, period 2), argon (group 18, period 3), fluorine (group 17, period 2) and chlorine (group 17, period 3). Recommend which gases to use and which to reject. Justify each choice using group, period and outer electrons.
Match each part of the table to its description
Group 1 (alkali metals) → C; Group 17 (halogens) → A; Group 18 (noble gases) → E; Group 2 (alkaline earth metals) → B; Period 3 → D.
1. Group 2: a calcium atom has two outer-shell electrons (so it behaves like other group 2 metals such as magnesium). Period 4: its electrons are in four shells. [2 marks]
Odd one out
Row 1: 2,5 (nitrogen); the other three have three shells, so they are in period 3 (Al, Cl, Na). Row 2: 2,8,8 (argon); the other three have two shells, so they are in period 2 (C, F, Be). Row 3: 2,8,2 (magnesium); the other three have a full outer shell, so they are in group 18 (He, Ne, Ar).
Go Deeper
2. P group 2; Q atomic number 17, Cl; R period 4; S Ne, period 2; T atomic number 14. Box P: 12 electrons arranged 2,8,2 fill three shells, so period 3. [4 marks: 3 for all seven cells (2 for five or six, 1 for three or four), 1 for the 2,8,2 reasoning]
3. Search by group: elements in group 17 have the same number of outer electrons, so they behave in similar ways. She would find fluorine or bromine (or iodine). Searching by period would give elements with the same number of shells but different behaviour. [3 marks: 1 by group, 1 correct element, 1 reason]
Show What You Know
4. Marking guide (points expected): 1 neon and argon are both in group 18, so both have a full outer shell; 1 so they are very unreactive and will not react with the metal parts (noble gases are used in lights and signs for this reason); 1 fluorine and chlorine are in group 17 (halogens), so they are reactive and would attack the parts; 1 the periods (2 and 3) only tell the number of shells, and each period contains one gas to use and one to reject, so period does not decide; 1 clear recommendation: use neon or argon, reject fluorine and chlorine. [5 marks]
Common error to watch for: in odd-one-out row 3, grouping helium (2) with magnesium (2,8,2) because both end in 2. Helium’s only shell is full, which is why it sits in group 18.