Periodic Trends: Ionisation Energy & Reactivity

Active learning works well for this topic because students often struggle with abstract concepts like nuclear charge and electron shielding. Hands-on graphing, reactions, and sorting let them see trends in real data and physical changes, building lasting understanding rather than memorization.

• Year 11
• Chemistry
• 4 activities
• 25 min–45 min

Learning Objectives

1. Explain the factors that determine the first ionisation energy of an element across a period and down a group.
2. Compare the trends in ionisation energy with the reactivity of alkali metals and halogens.
3. Predict the tendency of elements to form positive or negative ions based on their ionisation energies.
4. Analyze graphical data of ionisation energies to identify patterns and exceptions within the periodic table.

Concept Mapping

⏱ 45 min·Small Groups

Graphing Stations: Ionisation Trends

Prepare stations with data tables for Periods 2-3 and Groups 1, 7. Small groups plot line graphs for ionisation energy across periods and down groups, label axes accurately, and note anomalies such as Group 2 or 13 drops. Groups present one key trend to the class.

Prepare & details

Explain the factors influencing first ionisation energy across a period and down a group.

Facilitation Tip: During Graphing Stations, circulate and ask groups to explain any dips in their line, connecting them to electron configurations.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Concept Mapping

⏱ 30 min·Pairs

Reactivity Pairs: Metal Displacement

Pairs test magnesium, zinc, iron, and copper with dilute hydrochloric acid in test tubes. They time bubble rates, rank reactivity, and link to ionisation energy trends down transition metals. Record results in a class reactivity series table.

Prepare & details

Compare the reactivity of metals and non-metals based on ionisation energy trends.

Facilitation Tip: In Reactivity Pairs, time each trial and challenge students to explain why lithium reacts slower than potassium.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Concept Mapping

⏱ 35 min·Small Groups

Prediction Sort: Element Cards

Distribute cards with element symbols, positions, and properties. Small groups sort into sequences by predicted ionisation energy or reactivity, justify using shielding and radius rules, then test predictions against data handouts.

Prepare & details

Predict how ionisation energy changes will affect an element's tendency to form ions.

Facilitation Tip: For Prediction Sort, ask students to justify their placements aloud so peers hear multiple reasoning paths.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Concept Mapping

⏱ 25 min·Whole Class

Flame Demo Discussion: Group 1

Whole class observes teacher demo of lithium, sodium, potassium with water, noting vigour increase. Students discuss and sketch electron configurations, predicting ionisation energy order and reactivity reasons on mini-whiteboards.

Prepare & details

Explain the factors influencing first ionisation energy across a period and down a group.

Facilitation Tip: Use the Flame Demo to highlight the vivid colors and link them to low ionisation energies and rapid reactions.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Teaching This Topic

Teach this topic by building from observations to rules. Start with Group 1 flame tests to show reactivity visually, then connect to ionisation energy data. Avoid introducing shielding or nuclear charge too early; let students discover these concepts while analyzing trends. Research shows that students grasp periodic trends better when they first experience the extremes of reactivity before analyzing the underlying causes.

What to Expect

Successful learning looks like students correctly plotting ionisation energies, explaining reactivity changes through electron removal or addition, and predicting element behavior using periodic trends. They should justify answers with evidence from their graphs, experiments, and card sorts.

Watch Out for These Misconceptions

Common Misconception

During Graphing Stations, watch for students plotting a steady rise in first ionisation energy across a period without noting drops at Group 13 or Group 16.

What to Teach Instead

Ask these groups to revisit their graphs and explain why the trend isn’t perfectly smooth. Have them reference electron configurations and pair repulsion to correct their lines.

Common Misconception

During Reactivity Pairs, watch for students claiming Group 1 metals become less reactive down the group because their atoms are larger.

What to Teach Instead

Challenge them to time their reactions and note the speed differences. Then, ask them to link their observations to ionisation energy data from the graphing stations to deepen their reasoning.

Common Misconception

During Prediction Sort, watch for students incorrectly grouping all non-metals as low ionisation energy elements.

What to Teach Instead

Have these students refer to a filled periodic table and ask them to sort halogens separately, using their card sort data to explain why high ionisation energies don’t mean low reactivity for non-metals.

Assessment Ideas

Quick Check

After Graphing Stations, collect students’ completed periodic tables with arrows and written explanations to check their understanding of ionisation energy trends and reasons.

Discussion Prompt

During Reactivity Pairs, ask students to explain why sodium forms a +1 ion while chlorine forms a -1 ion, linking their answers to trends in ionisation energy and electron affinity.

Exit Ticket

After the Flame Demo Discussion, give students the symbols for Potassium (K) and Calcium (Ca) and ask them to predict which has higher first ionisation energy and explain their reasoning.

Extensions & Scaffolding

• Challenge early finishers to predict and test the reactivity of Group 2 metals with water, extending the displacement trend.
• For students who struggle, provide a scaffolded graph with key points labeled and ask them to connect data points and trends.
• Use extra time to explore anomalies like the drop from Group 2 to Group 13, asking students to research exceptions and present findings.

Key Vocabulary

Ionisation Energy	The minimum energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous positive ions.
Nuclear Charge	The total positive charge of the protons in the nucleus of an atom, which increases with the atomic number.
Electron Shielding	The repulsion between inner shell electrons and outer shell electrons, which reduces the effective nuclear charge experienced by the outer electrons.
Atomic Radius	A measure of the size of an atom, typically the mean distance from the center of the nucleus to the boundary of the surrounding electron cloud.