Lesson focus: Lithium, sodium and potassium form a chemical family because each has one outer electron; increasing shieldingWhen inner electrons block some of the pull of the nucleus on the outer electrons. makes that electron easier to remove down Group 1.
Use evidence and electron configurations to explain and predict Group 1 trends.
Build on earlier learning
The elements of Group 1Year 8 compared alkali-metal observations. This IGCSE Bridge lesson explains the pattern using electron structure.
Practical
Group 1 reactions
- Watch a demonstration of lithium, sodium and potassium in water.
- Compare the speed of the reaction and the flame colour.
- Test the solution with universal indicator.
Record: Observations linked to the trend in reactivity down the group.
Safety: Demonstration only, behind a safety screen.
You will be successful when you can…
- Describe reactions with water.
- Write the general products.
- Explain the reactivity trend.
- Predict cautiously beyond observed elements.
Words that carry the science
- alkali metal
- A Group 1 metal whose reactions commonly form alkaline solutions.
- hydroxide
- A compound containing OH⁻ ions.
- shielding
- Reduction in nuclear attraction for an outer electron due to inner electron shells.
- reactivity trend
- A systematic change in readiness to react through a group.
- alkaline
- Describes an aqueous solution with pH greater than 7 and available OH⁻ ions.
- prediction
- A reasoned expectation based on a supported pattern.
Water reactions reveal a chemical family
01Water reactions reveal a chemical family
Lithium, sodium and potassium float, move and react with water to form hydrogen gas and a metal hydroxideA compound containing oxygen and hydrogen joined as OH, found in alkalis such as sodium hydroxide. solution: metal + water → metal hydroxide + hydrogen.
The solutions are alkalineHaving a pH above 7, like soap or toothpaste. because they contain hydroxide ions. Tests must use tiny pieces, eye protection and a safety screen; these reactions are teacher demonstrations or evidence simulations.
02Reactivity increases down Group 1
Lithium fizzes steadily, sodium reacts faster and often melts into a ball, and potassium can ignite with a lilac flame. Stored samples must be compared with awareness of oxide coatings and piece size.
Down the group, atoms have more occupied shells. Greater distance and shieldingWhen inner electrons block some of the pull of the nucleus on the outer electrons. weaken attraction between the positive nucleus and the outer electron, so that electron is lost more readily.
03Predictions require bounded evidence
Rubidium and caesium are predicted to react still more vigorously based on electron structure and the established trend. This does not justify classroom testing.
Group membership supports similar products and ion charge (+1), while trend evidence supports differences in rate and violence. predictionWhat you think will happen, and why, before you do the test. should state the pattern, mechanism and safety limit.
Group 1 metals with water
The alkali metals react with water to make a metal hydroxide (an alkali) and hydrogen gas. They get more reactive down the group: lithium fizzes, sodium whizzes around, potassium bursts into flame.
Universal indicator: green (neutral) turns purple as the alkali forms. Small circles: hydrogen bubbles.
Controls
Speeds in the animation are illustrative. Rubidium and caesium react explosively, so they are never used in school.
Explain sodium versus lithium
Why does sodium react faster with water than lithium?
- Both atoms have one outer electron and form +1 ions.
- Sodium has one more occupied electron shell.
- Its outer electron is farther from the nucleus and more shielded.
- Nuclear attraction is weaker overall, so the electron is lost more readily.
How to make the reasoning visible: Faster electron loss supports the greater reactivity of sodium.
Group 1 evidence
Interpret standardised observations from equal-sized, freshly cut samples in water.
| Metal | Configuration | Observation | Evidence claim |
|---|---|---|---|
| lithium | 2,1 | steady fizzing | reactive |
| sodium | 2,8,1 | rapid movement; melts | more reactive |
| potassium | 2,8,8,1 | very rapid; lilac flame | most reactive tested |
| rubidium | 2,8,18,8,1 | not tested here | predicted more reactive |
Why must sample size and surface condition be controlled?
What gas forms and how is it identified?
Check your understanding
Answer from memory, then check against the suggested answer.
What are the products with water?
How does reactivity change down Group 1?
What charge do Group 1 ions have?
Predict how rubidium reacts with water and justify without recommending a test.
Why does increased proton number not reverse the trend?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Lithium, sodium and potassium are in Group 1. Each reacts with water.
Describe the similarities in their reactions.
(2)Explain the trend in reactivity.
(4)Total for this question: 6 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., give observations, products and the complete electron-structure mechanism.