Year 7 Science · Unit 2 · Lesson 5
Challenge Worksheet
Learning Goals
Design a mini-experiment
A scientist wants to test: "Can we predict the chemical reactivity of an unknown alkali metal (Group 1) by knowing only its position in the periodic table?" Plan the investigation below.
Background
You have been given samples of lithium (Li, Period 2), sodium (Na, Period 3), and potassium (K, Period 4) — all Group 1 alkali metals. A fourth element (rubidium, Rb) is available but its properties are unknown to you. Each element can be added to water, and the reaction's vigour (fizzing, heat, speed) can be observed. The lesson states that elements in the same group behave similarly, and reactivity increases as you go DOWN Group 1.
| What I will change (independent variable) | |
| What I will keep the same (controlled variables — list 3) | |
| What I will measure or observe (dependent variable) | |
| My prediction for rubidium's reactivity, based on its position in Group 1 (Period 5) | |
| How I would know if my prediction is wrong | |
| One safety concern with this experiment |
If this experiment supports the prediction, what does it tell us about the usefulness of the periodic table as a scientific tool?
1. Francium (Fr) is a Group 1 element found in Period 7 — below rubidium and caesium on the periodic table. Using only its position in the periodic table, predict two properties of francium. Justify each prediction by referring to the pattern you used.
2. Mendeleev organised elements by atomic mass, but the modern periodic table orders them by atomic number. Why might ordering by atomic number produce a more reliable pattern of properties? Think about what atomic number actually represents (protons) versus atomic mass.
Wrap Up
In one sentence, what was the main idea of this lesson?