Topic Five (1.5): Ionisation Energies and Periodicity

 Introduction

The ease with which an atom can lose (an) electron(s) is the key factor in determining the element’s reactivity so underpins your understanding of chemistry. You need to imagine the nucleus of the atom surrounded by shells containing electrons. Then the electrons are pulled off, one by one. The energy required to do this increases as we get nearer to the positive nucleus. We can represent this process in graphical form and you need to be able to interpret these graphs. Remember a full quantum shell gives the atom stability (and a half full shell a degree of this) and this is reflected in the graphs of ionisation energy.

 Reading

Edexcel AS/A Level Chemistry Student Book 1 pages 24 to 29, pages 32 to 33

 Tasks

Complete the following:

• Read pages 24 to 29, making appropriate notes. Pay particular attention to Figure C on page 28. You are often asked to reproduce this in an exam.
• Complete the ‘in-text’ questions.

WATCH – Periodic Trends Rap (YouTube) Links to an external site.

WATCH – Trends of The Periodic Table (Khan Academy) Links to an external site.

WATCH – Ionisation Trends of the Periodic Table (Khan Academy) Links to an external site.

DOWNLOAD – Infographic Trends in the Periodic Table Download DOWNLOAD – Infographic Trends in the Periodic Table

• Complete questions 2, 3, 7 and 8 on pages 32 to 33.

REVIEW – Learning Outcomes for Module One Download REVIEW – Learning Outcomes for Module One

Use this as a checklist to assess your knowledge.

 Top Tips

Make sure that you understand the following key points:

• When interpreting graphs remember you are working from the outer-most shell inwards (imagine skinning an onion).
• Look for the biggest “jumps”. These represent moving into a new quantum shell. If the jump occurs after three electrons are removed the element will be in group 3.
• Remember species involved are always in the gaseous state.
• You should know the definitions AND the equations of ionisation energies.

 Key Terms

Add the following subject vocabulary with definitions to your glossary.

• First ionisation energy
• Second ionisation energy
• Third ionisation energy
• Periodic properties

 Consolidate

Extend your understanding by working through these additional resources/tasks:

• Practise sketching the graphs of atomic number vs ionisation energy.

 Assignment

When you have completed all the activities and are fully prepared and feel confident with the material, you should complete Assignment One and submit it to your tutor via Canvas for marking and feedback.