Year 8 Science · Unit 2 · Lesson 15
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Each word is used once at most. Two words will not be used.
A column in the periodic table is called a and a row is called a . Elements in the same column can share some properties, but they are not . Going down Group 1, the reactivity of the metals . Going down any group, atoms get larger because they have more electron .
Put the Group 1 metals in order of reactivity
Number the metals from 1 (least reactive) to 4 (most reactive). In the last column, describe what happens when a small piece is dropped into water (for rubidium, predict).
| Order (1–4) | Metal | What you see in water |
|---|---|---|
| Rubidium (Rb) | ||
| Potassium (K) | ||
| Lithium (Li) | ||
| Sodium (Na) |
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Atomic radius increases as you go down a group.
Correct it:
2. Going across a period from left to right, the atoms get smaller.
Correct it:
3. In Group 17, iodine (near the bottom) is more reactive than fluorine (at the top).
Correct it:
4. Sodium and potassium are in the same group but in different periods.
Correct it:
Read the data
| Element | Period | Atomic radius (pm) |
|---|---|---|
| Lithium (Li) | 2 | 152 |
| Sodium (Na) | 3 | 186 |
| Potassium (K) | 4 | 227 |
| Rubidium (Rb) | 5 | 248 |
Atomic radius is how big an atom is. A picometre (pm) is a tiny unit of length used for atoms. Real values, rounded to whole numbers.
1. Which element in Table 1 has the largest atoms? Give its atomic radius with the unit.
2. Describe the pattern in Table 1 and give the reason for it. Caesium (Cs) sits directly below rubidium: predict whether its atoms are larger or smaller than 248 pm.
Scenario: one video, one big claim
Jai watched a video of a small piece of lithium in water. It fizzed slowly with small bubbles. Jai wrote: “Lithium reacts gently, so all Group 1 metals react gently with water.”
3. Explain why Jai’s statement is an overclaim. Use what happens when sodium and potassium are added to water as evidence, then rewrite Jai’s statement as a cautious, accurate statement.
Fill the gap
group; period; similar; identical; increases; shells. Not used (2): decreases, protons.
Put the Group 1 metals in order of reactivity
Reading down the table as printed: 4, 3, 1, 2.
Observations: rubidium, predicted to react even more violently than potassium (accept any answer saying more violent than potassium); potassium, reacts violently and ignites with a lilac flame; lithium, reacts gently with slow bubbles; sodium, reacts more vigorously, melts and skitters across the surface.
True or false
1. True. 2. True. 3. False: reactivity decreases down Group 17, so fluorine is more reactive than iodine. 4. True.
Read the data
1. Rubidium, 248 pm. [2 marks: 1 element, 1 value with unit]
2. Atomic radius increases going down the group (152 pm for lithium up to 248 pm for rubidium). Each element lower down has more electron shells, so its atoms are larger. Caesium is lower still, so its atoms should be larger than 248 pm. [3 marks: 1 pattern, 1 reason, 1 prediction]
Show What You Know
3. Marking guide (points expected): 1 one example cannot show what a whole group does; 1 sodium reacts more vigorously, melting and skittering across the water; 1 potassium reacts violently and ignites with a lilac flame, so “gently” is wrong for the group; 1 a cautious rewrite, for example “Group 1 metals tend to react with water, and the reaction becomes more vigorous going down the group.” [4 marks]
Common error to watch for: in the T/F item on Group 17, applying the Group 1 rule (“lower means more reactive”) to the halogens. The two groups run in opposite directions.