A Level Chemistry Revision "First Ionisation Energy"

Introduction

This tutorial is designed to help A Level Chemistry students understand the concept of first ionisation energy. This topic is often challenging, but breaking it down into manageable parts can clarify its importance and application in chemistry. By the end of this guide, you will have a solid grasp of what first ionisation energy is and how it relates to successive ionisation energies.

Step 1: Understand First Ionisation Energy

First ionisation energy is defined as the amount of energy required to remove the most loosely bound electron from a neutral atom in its gaseous state.

Key Points:

• Energy Requirement: It is always measured in kilojoules per mole (kJ/mol).
• Gaseous State: The atom must be in a gaseous state for the measurement to be accurate.
• Example: For sodium (Na), the first ionisation energy can be represented by the equation:

  Na(g) → Na⁺(g) + e⁻
  

Practical Advice:

• Visualize the process by thinking of the atom as a nucleus surrounded by electrons. The first ionisation energy involves overcoming the attraction between the nucleus and the outer electron.

Step 2: Explore Factors Affecting Ionisation Energy

Several factors influence the first ionisation energy of an element.

Factors:

1. Nuclear Charge: Greater positive charge in the nucleus increases the attraction to electrons, resulting in higher ionisation energy.
2. Distance from Nucleus: Electrons further from the nucleus experience less attraction, leading to lower ionisation energy.
3. Shielding Effect: Inner electrons can shield outer electrons from the full effect of the nuclear charge, decreasing ionisation energy.
4. Electron Configuration: Atoms with stable electron configurations (like noble gases) have higher ionisation energies.

Practical Advice:

• Create a chart comparing the ionisation energies of different elements to visualize these factors.

Step 3: Understand Successive Ionisation Energies

Once the first electron is removed, subsequent ionisation energies must be considered.

Key Points:

• Definition: Successive ionisation energies refer to the energy required to remove additional electrons from an atom after the first one has been removed.
• Trend: Generally, successive ionisation energies are higher than the first because the remaining electrons are attracted more strongly to the positively charged nucleus.

Practical Advice:

• Use the example of magnesium (Mg) to illustrate successive ionisation energies:

  Mg(g) → Mg⁺(g) + e⁻ (First Ionisation)
  Mg⁺(g) → Mg²⁺(g) + e⁻ (Second Ionisation)
  

Step 4: Recognize Trends in the Periodic Table

Ionisation energy varies across periods and groups in the periodic table.

Trends:

• Across a Period: Ionisation energy increases from left to right due to increasing nuclear charge and decreasing atomic radius.
• Down a Group: Ionisation energy decreases as additional electron shells increase distance from the nucleus and add shielding.

Practical Advice:

• Study the periodic table to identify these trends visually. Highlight groups and periods to reinforce your understanding of how ionisation energy changes.

Conclusion

Understanding first ionisation energy and its influencing factors is crucial for mastering A Level Chemistry. Remember that first ionisation energy is affected by nuclear charge, distance from the nucleus, shielding, and electron configuration. Successive ionisation energies also play a significant role and are generally higher due to increased nuclear attraction.

For further study, consider watching the subsequent videos that delve deeper into this topic. Engage with practice problems to apply what you’ve learned and solidify your understanding.