Today, we are going to discuss a very important concept in Atomic Structure and Chemical Bonding, known as Ionisation Energy.

We will start by looking at First Ionisation Energy, 1^st IE which allows you to deduce the Second Ionisation Energy, 2^nd IE and more.

You will also understand how to determine the maximum number of ionisation energies of an element in the Periodic Table.

First Ionisation Energy, 1^st IE

It is defined as the amount of energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of singly charged gaseous cations.

It can be represented by the following equation: X (g) → X⁺ (g) + e^–       ∆H₁ = 1^st ionisation energy = +ve

Second Ionisation Energy, 2^nd IE

It is defined as the amount of energy required to remove 1 mole of electrons from 1 mole of singly charged gaseous cations to form 1 mole of doubly charged gaseous cations.

It can be represented by the following equation: X⁺ g) → X²⁺ (g) + e^–       ∆H₂ = 2^nd ionisation energy = +ve

All the ionisation energies are positive values since energy is absorbed in removing an electron from an atom or ion.

Determination of the Maximum Number of Ionisation Energies of an Element

The number of ionisation energies that an element can have is always equal to the atomic number (proton number).

For example, oxygen has atomic number of 8 and thus the maximum ionisation energy of oxygen is until 8^th Ionisation Energy, 8^th IE.

Let’s take a look at the following YouTube Video for more examples on Ionisation Energy.

Length of video: 6.17 minutes

Direct video link: https://youtu.be/TJMSTNoR7lQ

From the video above, we have discussed about the formal definition of 1^st IE and as well other ionisation energies. We have also learned how to determine the maximum number of ionisation energies that are possible for an element.

3 important points to take note for Ionisation Energy:

1. Ionisation energies normally have positive values since energy is absorbed in removing an electron
2. Successive ionisation energies of an element increase with the removal of each electron because the remaining electrons are attracted more strongly by the constant positive charge on the nucleus
3. The number of ionisation energies that an element can have equals its atomic/proton number

For students taking the Singapore Cambridge GCE A-Level H2 Chemistry syllabus, you can observe the above 3 points in your Chemistry Data Booklet given by your JC Chemistry Tutors or our JC A-Level H2 Chemistry Tuition Classes. You can also download them at Singapore Examination & Assessment Board (SEAB) website. A sample page of ionisation energy is shown below.

Now, how about testing yourself on what we have just discussed?

Quick Check 1:

How many ionisation energies can Aluminium (proton number 13) have?

Quick Check 2:

Write the equation for the 7^th ionisation energy for Oxygen (proton number 8).

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends. This topic is usually discussed in JC1 (Junior College Year 1) in Singapore.

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PS: Under related articles below, there are several blog post discussions and questions related to Atomic Structure and Ionisation Energies. You can also do a keyword search using the search box at the top right hand corner.

Related Articles:

• Atomic Structure: Ionisation Energy
• Chemical Energetics: Definitions of Standard Enthalpy Changes of Reactions
• Sub-Atomic Particles of Atoms
• Atomic Structure: 3 Factors Affecting Ionisation Energy
• Atomic Structure: Number of Orbitals & Electrons in Quantum Shells

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Sean Chua

Winners Education Centre Pte. Ltd.

Many know me as the Ten Year Series book author for JC A-Level H2 Chemistry and O-Level Pure Chemistry. My 19+ years of coaching experience (since 1999) with more than 1500 students from 180+ JCs and Secondary Schools has allowed me to understand the true reasons why students are not able to perform well in Chemistry. Most importantly, my strength lies in using everyday analogies (even grandmothers can understand!) to simplify abstract concepts. Also, my teaching methodology has been designed to be fun, enjoyable and effective for my students.

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